ORCID Profile
0000-0002-4517-435X
Current Organisation
University of Western Australia
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Psychology | Sensory Processes, Perception and Performance | Sensory Processes, Perception And Performance | Sensory Systems | Sensory Systems | Opthalmology And Vision Science | Neurosciences | Diagnostic Applications | Knowledge Representation and Machine Learning | Intelligent Robotics
Expanding Knowledge in Psychology and Cognitive Sciences | Behavioural and cognitive sciences | Air Force | Medical instrumentation | Biological sciences |
Publisher: Springer Science and Business Media LLC
Date: 11-1988
DOI: 10.3758/BF03207489
Abstract: The Pt(II) ion in the title complex, [PtBr(2)(C(14)H(10)N(4))], is four-coordinated in a distorted square-planar environment by two N atoms of a chelating 2,3-di-2-pyridyl-pyrazine ligand and two bromide anions. In the crystal, the pyridyl ring coordinated to the Pt atom is inclined slightly to its carrier pyrazine ring [dihedral angle = 14.7 (2)°], whereas the uncoordinated pyridyl ring is inclined considerably to the pyrazine ring [dihedral angle = 51.9 (3)°]. The dihedral angle between the two pyridyl rings is 57.7 (3)°. Two complex mol-ecules are assembled through inter-molecular C-H⋯N hydrogen bonds, forming a dimer-type species. Intra-molecular C-H⋯Br and C-H⋯N hydrogen bonds are also present.
Publisher: Elsevier BV
Date: 1990
DOI: 10.1016/0042-6989(90)90143-9
Abstract: Differences of less than 20 sec of visual angle in the separation of a pair of closely spaced parallel lines can be reliably detected. This ability is known as a hyperacuity because the thresholds are smaller than the diameter of one foveal cone. It is shown that this ability does not require a stationary pattern. Indeed, correlated horizontal jitter of the line pair has little detrimental effect on performance for jitter that ranges up to 8 min arc for two lines with a separation of only 6 min arc. Uncorrelated jitter of the two lines, which allows the actual separation to vary from moment to moment, causes performance to deteriorate at a rate similar to the rise of signal uncertainty. The results reflect the operation of a system which is not only extremely robust to oculomotor instability but is also robust to positional variation that could not be produced by eye movements.
Publisher: Elsevier BV
Date: 1985
DOI: 10.1016/0042-6989(85)90010-0
Abstract: Grating having two sinusoidal components show a periodic variation in contrast which is visible as a "beat" pattern. The spatial frequency of the beat is the difference between the frequencies of the two components. Thresholds for a number of detection and discrimination tasks were measured using beat patterns of 1 c/deg (with components of 9 and 10 c/deg), and gratings of 1 and 10 c/deg. Temporal modulation at 6 Hz lowered detection thresholds for 1 c/deg gratings, but not for beats or 10 c/deg gratings. The effect of contrast on the range of temporal frequencies over which direction of movement can be discriminated differs for the three types of pattern: beats resemble neither low nor high spatial frequency gratings. Low and (for 2 of 3 observers) high spatial frequency gratings, but not beat patterns, are susceptible to a movement after effect induced by a low spatial-frequency grating. Beat patterns induce little or no movement after effect. We conclude that beat patterns are not detected by the same mechanisms that detect simple gratings.
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 14-09-2016
DOI: 10.1167/16.11.10
Abstract: Radial frequency (RF) textures (created by applying a sinusoidal modulation of orientation to an otherwise circular texture) have been shown to be globally processed. RF textures differ from RF patterns (paths deformed from circular by a sinusoidal modulation in radius) in that the elements need not be constrained to a specific path. In the natural environment, objects differ from their background in texture, and a bounding contour can mark this textural change. This study examines the extent to which modulation of texture sums across space and whether the inclusion of a boundary between two areas provides a segmentation cue that limits the area over which summation occurs. RF textures were split into two annular regions and signal introduced to inner, outer, or both annuli Thresholds for the detection of RF modulation of orientation were not affected by the presence of a boundary. Further, it was found that the thresholds matched predictions for the independent contribution of the inner and outer areas to performance and that changing the relative phase of the modulation in the inner and outer annuli had no impact on performance, implying independent integration within the two annuli. Finally, integration of modulation information within the annuli was confirmed to ensure these results do apply to textures that are globally processed.
Publisher: SAGE Publications
Date: 06-2003
DOI: 10.1068/P5085
Abstract: Observations made during two partial eclipses of the Sun show that the Mach bands on shadows cast by the Sun disappear and reappear asymmetrically as an eclipse progresses. These changes can be explained as due to changes in the shape of the penumbras of shadows as the visible portion of the Sun forms crescents of different orientation.
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 28-11-2012
DOI: 10.1167/12.12.16
Abstract: Radial frequency (RF) patterns, paths deformed from circular by a sinusoidal modulation of radius, have proved valuable stimuli for investigation of visual shape processing. Their utility relies upon evidence that thresholds for detection of modulation decrease, as cycles of modulation are added, at a rate that cannot be accounted for by the improving probability of detection of any single cycle (probability summation). This has been interpreted as indicative of global processing. Recently Mullen, Beaudot, and Ivanov (2011), using low contrast RF patterns viewed in cosine phase through a Gaussian window, demonstrated the existence of a local cue to modulation that was more salient than the global shape cue present in sectors of RF patterns. The experiments reported here investigate why this cue has not previously obscured global integration of shape information in RF patterns. Using stimuli modulated in sine phase, Experiment 1 showed that the presence of a circular sector of path, used to complete a partially modulated RF pattern, does not raise thresholds, contrary to the suggestion of Mullen et al. (2011). Experiment 2 demonstrated integration for high and low contrast RF patterns viewed in sine phase through a Gaussian window and Experiment 3 showed the same for patterns in cosine phase if the use of a local phase specific curvature cue was precluded. Effective use of local curvature in the test comparison, then, requires knowledge of pattern orientation to define the sign of curvature. Experiment 4 demonstrated global processing of shape information for a range of radial frequencies and also showed that the local maximum gradient with respect to circular within an RF pattern covaries with threshold. This implies that it is this cue, or one that covaries linearly with it, that is integrated across cycles of modulation by the global processing mechanism.
Publisher: The Electrochemical Society
Date: 19-05-2023
Abstract: In this work, the A-site of the common SOFC cathode La 0.8 Sr 0.2 MnO 3-δ (LSM) is modified with additional lanthanide and alkali elements, resulting in the composition (La 1/6 Pr 1/6 Nd 1/6 Gd 1/6 Ba 1/6 Sr 1/6 )MnO 3- δ . We show that the amount of oxygen released during reduction measured by thermo-gravimetric analysis is significantly greater for this “high entropy” perovskite oxide (HEPO) in comparison with La 2/3 Sr 1/3 MnO 3-δ , the latter having the same amount of total acceptor dopant and with a similar average A-site radius. The origins of enhanced reduction will be discussed.
Publisher: Elsevier BV
Date: 09-2009
DOI: 10.1016/J.VISRES.2009.06.022
Abstract: Combinations of radial frequency (RF) patterns may be used to represent the contours of complex shapes. Previous work has shown that many radial frequency patterns are processed globally and multiple curvature mechanisms have been proposed to account for human performance in detecting these patterns. The current paper provides a direct test of this proposal and also, investigates how different RF mechanisms interact when forming a single complex contour. To test for interactions, pairs of RF components have been combined on a closed contour to create a compound pattern. Deformation detection thresholds for single RF components were compared to thresholds for detecting that component in a compound. Masking was present, and was not tuned for the phase relationship between components but was instead tuned for RF, consistent with the existence of several narrow-band shape channels which have inhibitory connections between them. Adaptation was then used to selectively desensitise channels. Adapting to a single RF pattern reduced sensitivity to RF patterns of the same frequency but restored sensitivity to a dissimilar RF component on the compound contour. The effects were shown to be independent of the mean radius of the adaptor, and also occurred when adaptors were contours composed of contrast modulated noise, suggesting that post-adaptation results are not simply due to adaptation of local V1 orientation-tuned simple cells. The data are consistent with two or more shape channels for closed-contours, which operate in a competitive network.
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 16-12-2013
DOI: 10.1167/13.14.12
Abstract: The human visual system's extreme sensitivity to subtle changes in shape can often be attributed to global pooling of local information. This has been shown for shapes described by paths of contiguous elements, but it was unknown whether this global pooling translated to shapes defined by texture-segmentation borders. Also, previous research suggests that texture and luminance cues-to-shape are integrated by the visual system for shape detection but it has not been established whether they combined for shape discrimination. Controlled shapes defined either by an explicit path of Gabors, texture-segmentation borders, or both of these cues were used. Results show that all stimuli used were globally processed. Thresholds for shapes defined by both cues matched predictions based on an independent-cue vector sum of in idual thresholds. Thus, while local elements are integrated around the contour and are processed by global shape-detection mechanisms, integration did not occur across different shape-cues.
Publisher: Elsevier BV
Date: 08-2003
DOI: 10.1016/S0042-6989(03)00307-9
Abstract: Two important tasks that the visual system has to perform are determining the direction of motion and the spatial location of objects. It has recently been shown that the perceived location of an object moving in the frontal-plane is displaced along the direction of motion (e.g. Nature 397 (1999) 610 Vision Research 31 (1991) 1619). The aim of the present study is to examine the extent of this interaction between motion and perceived location. The observers' task was to indicate which of two vertically separated moving stimuli was closer. The two stimuli were presented at various relative disparity offsets. The stimuli consisted of moving dot patterns (optic-flow) that simulated either fronto-parallel motion (all the dots moved one direction) or motion in depth. Motion of the dots towards the centre of the stimulus simulated object motion away from the observer and motion of the dots away from the centre of the stimulus simulated object motion towards the observer. Results indicate that motion-in-depth information can bias perceived stereoscopic-based depth. Simulated motion towards the observer made the object appear closer to the observer than the depth signalled by the disparity information and simulated motion away from the observer made it seem further away. The results of this study, when combined with those of previous studies, show that motion can distort our entire three dimensional representation of space.
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 07-2006
DOI: 10.1167/IOVS.05-1549
Abstract: A recent study has demonstrated that some people with migraine display impairments of intermediate stages of motion and form processing. Deficits were identified by using tasks that required that local stimulus attributes be integrated into global percepts. Neurons capable of global processing of form and motion are known to be present in extrastriate cortical areas V4 and V5, respectively. It is not clear from the literature whether deficits of global processing in migraineurs are likely to arise from reduced input to extrastriate cortex from primary visual cortex (V1). The purpose of the study was to compare presumed measures of V1 performance (vernier acuity) to measures of global form and motion perception in migraineurs. Thirty migraineurs (17 with aura, and 13 without) and 20 age-matched nonheadache control subjects participated. Intermediate level motion and form perceptions were measured using global dot motion stimuli and Glass patterns, respectively. Vernier stimuli were broad vertical bars composed of small dot elements. Both a static luminance stimulus and a motion defined form vernier stimulus were used. Mean migraine and control group performance were not significantly different for either vernier task (static: t(48)=0.39, P=0.70 motion: t(48)=0.29, P=0.77). Mean migraine group performance was significantly worse than in control subjects for both the global form (t(48)=2.06, P=0.04) and global motion (t(48)=2.87, P<0.01) tasks. On average, migraineurs demonstrate abnormalities of intermediate stages of both motion and form processing. These abnormalities do not appear to arise from dropout of performance at V1, as vernier acuity was normal in the same in iduals.
Publisher: Elsevier BV
Date: 1986
DOI: 10.1016/0042-6989(86)90032-5
Abstract: We measured sensitivity of human observers to the 1 c/deg beat between sinusoidal gratings of 9 and 10 c/deg, at different contrasts of the 2 components. Raising the contrast of one component increases the contrast required in the other component to detect the beat. This is consistent with the hypothesis that the beat is detected because of the local increments in contrast which it produces, but not with the hypothesis that it is detected when a difference-frequency distortion product generated by non-linear transduction of luminance reaches threshold.
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 11-11-2010
DOI: 10.1167/10.13.5
Abstract: Adaptation to prevailing stimuli is a ubiquitous property of the visual system that optimizes its dynamic range. The perceived difference in orientation of successively presented lines of similar orientation is exaggerated and the perceived shape of an object is influenced by previously experienced shapes. Change in perceived shape is assumed to arise through the adaptation of shape detectors. Here we consider an alternative: adaptation within a substrate of local oriented line detectors resulting in enhanced shape contrast in similar shapes. We show that the perceived shapes of a spatially coincident circle and Cartesian grid can be manipulated independently by adaptation to geometrically transformed copies of themselves. The same transformation was applied to the circle and the grid to create the adaptors therefore, the specificity of the effects of adaptation demonstrates that the visual system adapts to the shape of objects rather than applying transformations to the reference frame of the visual field. The tilt aftereffect predicts local changes in perceived orientation, and fields of such local effects can often account for the global change in perceived shape of complex objects, including faces.
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 13-09-2016
DOI: 10.1167/16.11.9
Abstract: The modulation of orientation around radial frequency (RF) patterns and RF textures is globally processed in both cases. This psychophysical study investigates whether the combination-a textured RF path obtained by applying an RF texture to an RF contour-is processed like a texture or a contour when making judgements about shape. Unlike RF textures, the impression of a closed flow was not required for global integration of textured RF paths, suggesting that these paths were processed as second-order, or contrast-defined contours. Luminance-defined (LD) RF paths were shown to globally integrate but with thresholds approximately half of those for the proposed second-order textured paths. The next experiment investigated whether this benefit was due to LD stimuli possessing double the amount of information (first- and second-order information). A mixed three-part contour composed of two different second-order texture components and an LD component was then employed to determine how the different cues combined. The mixed path thresholds matched predictions derived from a linear combination of first- and second-order cues. The conclusion is that the shape of isolated contours is processed using both first- and second-order information equally and that the contribution of texture is to carry additional second-order signal.
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 07-09-2016
DOI: 10.1167/16.11.6
Abstract: This study reevaluated the summation extent for moving stimuli using the Battenberg summation paradigm (Meese, 2010), which aims to circumvent internal noise changes with increasing stimulus size by holding display size constant. In the checkerboard stimulus, the size of the checks (luminance-modulated drifting gratings) was varied to measure dependence on signal area. Experiment 1 was a contrast detection task that used either signal checks alternating with uniform, mean luminance, checks (single-motion) or alternate checks containing gratings moving in opposite directions (opposing-motion). The latter was designed to test whether summation extent changes when segregating regions based on motion direction. Results showed summation over a square summation area with a side length of 3.33°, much larger than previous estimates of less than 1° for similar stimuli (Anderson & Burr, 1991). This was found for both motion combinations, providing no evidence that summation extent differs when segregating patterns based on direction, at contrast detection threshold. These results are in close agreement with those obtained for static patterns (Meese, 2010) and support the same underlying summation model. Experiment 2 was a contrast increment detection task conducted to determine whether differences in summation extent arise under suprathreshold contrast conditions. There was no dependence on check size for either condition across the range of sizes tested. This supports the suggestion that segmentation mechanisms dominate perception under high-contrast conditions, a potential adaptive strategy employed by the visual system.
Publisher: Elsevier BV
Date: 05-1996
DOI: 10.1016/0042-6989(95)00205-7
Abstract: The visual system commonly has to estimate the relative location of a textured region but the stimulus features used to perform that task are yet to be determined. The use of centroid, midpoint and peak activity cues would all be reasonable. In the current experiment an attempt was made to assess the relative efficacy of these three cues. The observers were required to indicate whether a cloud of either 3, 10 or 100 elements was located to the left or right of an imaginary line formed between two reference elements. Performance was compared to that expected from the use of the three cues. It was concluded that the cue used varied as the characteristics of the cloud changed and therefore that the visual system is not restricted to the use of a single cue type when localizing object clusters.
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 31-03-2017
DOI: 10.1167/17.3.27
Abstract: Size and aspect ratio are ecologically important visual attributes. Relative size confers depth, and aspect ratio is a size-invariant cue to object identity. The mechanisms of their analyses by the visual system are uncertain. In a series of three psychophysical experiments we show that adaptation causes perceptual repulsion in these properties. Experiment 1 shows that adaptation to a square causes a subsequently viewed smaller (larger) test square to appear smaller (larger) still. Experiment 2 reveals that a test rectangle with an aspect ratio (height/width) of two appears more slender after adaptation to rectangles with aspect ratios less than two, while the same test stimulus appears more squat after adaptation to a rectangle with an aspect ratio greater than two. Significantly, aftereffect magnitudes peak and then decline as the sizes or aspect ratios of adaptor and test erge. Experiment 3 uses the results of Experiments 1 and 2 to show that the changes in perceived aspect ratio are due to adaptation to aspect ratio rather than adaptation to the height and width of the stimuli. The results are consistent with the operation of distinct banks of information channels tuned for different values of each property. The necessary channels have log-Gaussian sensitivity profiles, have equal widths when expressed as ratios, are labeled with their preferred magnitudes, and are distributed at exponentially increasing intervals. If an adapting stimulus reduces each channel's sensitivity in proportion to its activation then the displacement of the centroid of activity due to a subsequently experienced test stimulus predicts the measured size or aspect ratio aftereffect.
Publisher: American Psychological Association (APA)
Date: 1990
Publisher: SAGE Publications
Date: 10-1987
DOI: 10.1068/P160641
Abstract: The technique of uniform field flicker (UFF) masking has frequently been used to address issues concerning the relative performance of sustained and transient neural channels in the human visual system. Unfortunately there has been an artifact in the implementation of this method in most published experiments which has meant that the contrast of the target has been flickered in synchrony with the mean luminance. A study is reported in which the artifact was corrected and the effects of UFF masking on the contrast sensitivity function then examined. With this correction, masking was still restricted to low spatial frequencies but it was much weaker than reported originally. It is argued that the original evidence suggesting that UFF masking can be used to examine the functioning of transient and sustained channels has not been interpreted correctly and that the basis for such a claim is weak.
Publisher: Springer Science and Business Media LLC
Date: 25-07-2013
DOI: 10.3758/S13423-013-0491-3
Abstract: The attentional blink (AB) refers to a deficit in reporting the second of two sequentially presented targets when they are separated by less than 500 ms. Two decades of research has suggested that the AB is a robust phenomenon that is likely attributable to a fundamental limit in sequential object processing. This assumption, however, has recently been undermined by a demonstration that the AB can be eliminated after only a few hundred training trials (Choi, Chang, Shibata, Sasaki, & Watanabe in Proceedings of the National Academy of Sciences 109:12242-12247, 2012). In the present work, we examined whether this training benefited performance directly, by eliminating processing limitations as claimed, or indirectly, by creating expectations about when targets would appear. Consistent with the latter option, when temporal expectations were reduced, training-related improvements declined significantly. This suggests that whereas training may ameliorate the AB indirectly, the processing limits evidenced in the AB cannot be directly eliminated by brief exposure to the task.
Publisher: Elsevier BV
Date: 12-2002
DOI: 10.1016/S0042-6989(02)00384-X
Abstract: A primary task of the visual system is to extract the direction and speed of animate objects from the retinal image. We examined global speed processing by determining how local speeds are integrated and whether integration occurs across all speeds or within fixed speed ranges. The first experiment addressed how local motion signals are combined to determine the speed of an object in motion. Observers judged the speed of a moving cloud of dots that took a random walk in direction while the dots inside the cloud moved somewhat independently of the cloud itself. The apparent speed of the cloud of dots is found to change in proportion with the dot speed and is well predicted by calculating the average speed resulting from nearest neighbour matches across stimulus frames. The second experiment addressed whether local speeds are combined across all speeds or within fixed speed ranges for the detection of global motion. Global dot motion (GDM) stimuli that moved in a radial or rotational directions moving at a low speed of 1.2 degrees /s or a high speed of 9.6 degrees /s were used to measure the thresholds for detecting structured motion as a function of the speed of noise dots (0 degrees /s-10.8 degrees /s) added to the stimulus. With low-speed targets, only additional noise dots moving at low speeds interfered with signal detection. High-speed targets were only interfered with by dots moving at high speeds. This finding established the existence of at least two independent speed tuned systems in the range of speeds tested. Experiment 3 investigated how speed signals are combined within a system to determine the global speed. Using sectored radial GDM stimuli the perceived speed of the fastest dots was measured as a function of whether the speed of the dots in alternate sectors either activated the high or low-speed systems. Averaging only occurred when dots were all within the sensitivity range of the high-speed system, however, if alternate sectors activated separate speed systems, averaging did not occur. Thus local speeds are averaged, independent of direction, to derive a global speed estimate, but averaging only occurs within, and not across, speed tuned mechanisms.
Publisher: Springer Science and Business Media LLC
Date: 09-1993
DOI: 10.3758/BF03204528
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 17-04-2012
DOI: 10.1167/12.4.8
Abstract: In order to interact with our environment, the human brain constructs maps of visual space. The orderly mapping of external space across the retinal surface, termed retinotopy, is maintained at subsequent levels of visual cortical processing and underpins our capacity to make precise and reliable judgments about the relative location of objects around us. While these maps, at least in the visual system, support high precision judgments about the relative location of objects, they are prone to significant perceptual distortion. Here, we ask observers to estimate the separation of two visual stimuli--a spatial interval discrimination task. We show that large stimulus sizes require much greater separation in order to be perceived as having the same separation as small stimulus sizes. The relationship is linear, task independent, and unrelated to the perceived position of object edges. We also show that this type of spatial distortion is not restricted to the object itself but can also be revealed by changing the spatial scale of the background, while object size remains constant. These results indicate that fundamental spatial properties, such as retinal image size or the scale at which an object is analyzed, exert a marked influence on spatial coding.
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 31-03-2015
DOI: 10.1167/15.3.17
Abstract: Radial frequency (RF) patterns, shapes deformed from circular by a sinusoidal modulation of radius, have been used to demonstrate global integration of shape information around a closed path by showing that the modulation depth required to detect shape deformation decreases rapidly as larger segments of the contour are modulated. In this psychophysical study we use a field of Gabor patches to examine integration of shape information in s led RF patterns either alone or placed within an orientation-noise background and show that orientation-noise can be disregarded during the integration of modulation information. We also examine integration in modulated textures with local orientations that flow parallel or perpendicular to an underlying RF shape-structure. In using modulated textures comprising of elements with a random radial position but with orientation modulated such that it conforms to the local orientation of an RF pattern (RF texture) we demonstrate integration around texture patterns that imply shape. Texture patterns with element orientations locally orthogonal (RFO textures) to those of RF textures, however, exhibit a rate of decrease in modulation threshold, which is substantially reduced. When the textures are scrambled by permuting the polar positions of the patches the rate of decrease in threshold with increasing number of patches modulated in orientation is reduced for RF textures but not RFO textures. Detection of modulation in both scrambled textures is shown to be consistent with the detection of local cues. We conclude that implied closure in a modulated flow appears to be critical for global integration of textures.
Publisher: Springer Science and Business Media LLC
Date: 29-07-2011
DOI: 10.3758/S13414-011-0185-8
Abstract: The ability to make accurate audiovisual synchrony judgments is affected by the "complexity" of the stimuli: We are much better at making judgments when matching single beeps or flashes as opposed to video recordings of speech or music. In the present study, we investigated whether the predictability of sequences affects whether participants report that auditory and visual sequences appear to be temporally coincident. When we reduced their ability to predict both the next pitch in the sequence and the temporal pattern, we found that participants were increasingly likely to report that the audiovisual sequences were synchronous. However, when we manipulated pitch and temporal predictability independently, the same effect did not occur. By altering the temporal density (items per second) of the sequences, we further determined that the predictability effect occurred only in temporally dense sequences: If the sequences were slow, participants' responses did not change as a function of predictability. We propose that reduced predictability affects synchrony judgments by reducing the effective pitch and temporal acuity in perception of the sequences.
Publisher: Elsevier BV
Date: 02-2021
DOI: 10.1016/J.VISRES.2020.11.001
Abstract: The perceived contrast of a central stimulus is reduced in the presence of a high contrast surround. A number of stimulus features influence the amount of suppression. A two-mechanism model has been proposed for stationary patterns involving a narrowly-tuned process, requiring very similar stimuli in the centre and surround, and a weaker, untuned or very broadly tuned process unselective for stimulus features. This study examines whether a similar model applies to the motion pathway in human participants by varying the orientation and direction of motion of the surround relative to the centre. Four experienced observers completed a two-interval forced-choice contrast matching task. The stimuli were drifting sinusoidal grating patterns with high contrast surrounds (95%) differing in direction of motion and orientation relative to the centre grating. All surround conditions produced suppression but a common orientation and direction of motion produced significantly more suppression than either opposite direction of motion conditions or orthogonal direction conditions. The tuning for motion direction differences was assessed for same and opposite directions of motion. These findings support the extension of the two-mechanism model of contrast suppression to motion direction.
Publisher: Brill
Date: 1988
Abstract: Changing the relative phase of the frequency components of a stimulus usually also produces local contrast variations. Using stimuli composed of the product of a sinusoid (carrier) and a spatial envelope, an attempt was made to distinguish between the visual system's ability to code spatial phase on the one hand and local contrast and position cues on the other. The experiments assess the ability of observers to detect which of two stimuli is farther to the left. In the main experiments a large, easily detectable, envelope shift is presented on every trial and performance is measured as a function of the size of a carrier shift in the same direction. Increasing the size of the carrier shift gradually increases the size of the phase difference between the two stimuli in a trial but simultaneously reduces the contrast change in the bars of the stimulus. If the visual system can code phase directly the ability of observers to detect a change in location should improve as the size of the carrier shift increases but if local contrast is coded performance should be poorer over a small range of carrier shifts than that obtained without a carrier shift. It is shown that a region of poorer performance is obtained and therefore it is concluded that the visual system does not code spatial phase explicitly.
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 31-08-2017
DOI: 10.1167/17.10.1367
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 28-09-2016
DOI: 10.1167/16.11.23
Abstract: The synchronous change of a feature across multiple discrete elements, i.e., temporal synchrony, has been shown to be a powerful cue for grouping and segmentation. This has been demonstrated with both static and dynamic stimuli for a range of tasks. However, in addition to temporal synchrony, stimuli in previous research have included other cues which can also facilitate grouping and segmentation, such as good continuation and coherent spatial configuration. To evaluate the effectiveness of temporal synchrony for grouping and segmentation in isolation, here we measure signal detection thresholds using a global-Gabor stimulus in the presence/absence of a synchronous event. We also examine the impact of the spatial proximity of the to-be-grouped elements on the effectiveness of temporal synchrony, and the duration for which elements are bound together following a synchronous event in the absence of further segmentation cues. The results show that temporal synchrony (in isolation) is an effective cue for grouping local elements together to extract a global signal. Further, we find that the effectiveness of temporal synchrony as a cue for segmentation is modulated by the spatial proximity of signal elements. Finally, we demonstrate that following a synchronous event, elements are perceptually bound together for an average duration of 200 ms.
Publisher: Elsevier BV
Date: 06-2000
DOI: 10.1016/S0960-9822(00)00524-8
Abstract: It is widely believed that form and motion are analysed separately in mammalian visual systems. Form is confined within a stream that projects ventrally from V1 to the inferotemporal cortex, and motion within a stream that projects more dorsally, to the posterior parietal cortex [1] [2] [3] [4] [5] [6] [7]. Current descriptions suggest that there is little contact between the two streams until the products of their separate analyses are bound together at a late (and still unidentified) stage in perception [3] [8] [9] [10]. There are, however, indications that form and motion signals may interact [11], and that form signals, streaks derived from motion, may assist in the analysis of its direction [12]. Lennie [13] proposes that all image attributes, form and motion included, remain intimately coupled within the same retinotopic map at all stages of visual analysis. Here we show that form, independent of motion, can give coherence to incoherent motion. Sequences of Glass patterns [14] built to a common global rule are devoid of coherent motion signals, but they produce motion consistent with the global rule for form, not with the random velocity components of the pattern sequence.
Publisher: Elsevier BV
Date: 10-2010
DOI: 10.1016/J.PSYCHRES.2009.09.002
Abstract: Spatial working memory (SWM) dysfunction is a central finding in schizophrenia however, more evidence of impaired maintenance over time is required. Consequently, the present study examined SWM maintenance over short unfilled delays, and with encoding equated. The influence of a vertical reference frame to support maintenance was also investigated. The performance of 58 patients with schizophrenia and 50 healthy controls was assessed using the Visuo-Spatial Working Memory (VSWM) Test across three unfilled delays (0, 2, and 4s). Inaccuracy of direction and distance responses was examined at each delay duration. The results showed that performance was significantly less accurate for both distance and direction responses at 2 and 4s delays in schizophrenia, but was not significantly different from controls at the 0s delay. Patients showed a particularly marked loss of accuracy between the time interval of 0-2s. Furthermore, schizophrenia participants exhibited significantly greater response variability at the vertical axis of symmetry than controls at the 2 and 4s delays, but not at the 0s delay. These data clearly show both impaired maintenance over time and difficulty using a vertical frame of reference in schizophrenia. The latter findings may reflect, in part, dysfunctional reference-related inhibition.
Publisher: Elsevier BV
Date: 2013
DOI: 10.1016/J.VISRES.2012.10.010
Abstract: This research investigated the effect of foreperiod predictability in the Attentional Blink (AB). The AB, a cost in processing the second of two targets presented in close temporal proximity, was estimated using a minimalist procedure consisting of two letter targets and two letter fragment masks. In a four-step procedure, differences in foreperiod duration, target exposure duration, and inter-target interval were controlled in order to estimate the AB. Foreperiod was manipulated in three experiments. The AB effect was reduced when a single and relatively long foreperiod value was used (M=880 ms, Experiment 2) in comparison to randomized (250-750 ms, Experiment 1) and single but relatively short foreperiods (M=273 ms, Experiment 3). The results are discussed in the context of resource-sharing and preparation of a perceptual-set pertaining to physical target features including modality and intensity, as well as spatial and temporal predictability. It is concluded that foreperiods that are too brief for an in idual observer or temporally unpredictable contribute to the AB.
Publisher: Elsevier BV
Date: 05-1994
DOI: 10.1016/0042-6989(94)90206-2
Abstract: The ability to judge the separation between two target lines deteriorates as the base separation increases. Several lines of evidence suggest that this may be due to larger base separations being processed by mechanisms that cover larger areas and which have a greater associated positional uncertainty as a consequence. Separation discrimination was measured as a function of base separation with randomly jittering targets. As predicted from the above models the resistance to positional noise increased in proportion to base separation of the targets. The data is incompatible with the suggestion that resistance to positional noise declines when the extent of the noise exceeds fixational instability.
Publisher: Elsevier BV
Date: 2013
DOI: 10.1016/J.VISRES.2012.10.015
Abstract: Local-motion information can provide either 1-dimensional (1D) or 2-dimensional (2D) solutions. 1D signals occur when the aperture problem has not been solved, so each signal is an estimate of the local-orthogonal component of the object's motion. 2D signals occur when the aperture problem has been solved, so each signal is an estimate of the object's motion. Previous research (JoV, 2009, 9, 1-25) has shown that 1D and 2D signals are pooled differently, via intersection-of-constraints (IOC) and vector-average processes, respectively. Previous research (e.g. Vis. Res., 2003, 2290-2301) has also indicated that form cues can influence how motion signals are perceived. We investigated whether forms cues can affect the pooling of motion signals and whether they differentially affect the pooling of 1D and 2D signals. Global-Gabor (GG) and global-plaid (GP) stimuli were used. These stimuli consist of multiple apertures that contain either Gabors or plaids, respectively. In the GG stimulus the global solution is defined by having the Gabor carriers move (1D signals) such that they are consistent with a single IOC-defined solution. In the GP stimuli the plaid motion (2D signals) are consistent with a vector-average solution defined by a Gaussian distribution. Form cues can be introduced by adding orientation information to the apertures that is either consistent (aligned with) or inconsistent (orthogonal to) with the global-solution. With the 1D stimuli, form cues affect how the motion signals are pooled, with motion being perceived in the direction defined by the orientation cue. Orientation cues had no direct effect on the pooling of the 2D signals.
Publisher: SAGE Publications
Date: 09-2006
DOI: 10.1111/J.1468-2982.2006.01182.X
Abstract: Migraine groups have impaired ability to identify global motion direction in noisy random dot stimuli, an observation that has been used as evidence for cortical hyperexcitability. Several studies have also suggested abnormalities in cognitive processing, particularly in the domains of attention, visuo-spatial processing and memory. This study aimed to determine whether poor performance by migraineurs in motion coherence tasks could be explained by non-visual cognitive factors such as attention. Twenty-nine migraineurs and 27 non-headache controls participated. Global motion coherence thresholds were measured along with measures of neuropsychological function, using the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS). The migraine group had significantly higher motion coherence thresholds than controls. No significant difference in attention or any other RBANS index score was found between groups. Index scores did not correlate with motion perception thresholds. This study does not support inattention or other cognitive abnormality as an explanation for motion perception anomalies in migraine.
Publisher: SAGE Publications
Date: 05-2004
DOI: 10.1111/J.1468-2982.2004.00682.X
Abstract: We have previously demonstrated that perimetric performance measured with flickering stimuli is not normal in some in iduals who experience migraine with aura in the period between their attacks. In this study, flicker perimetric performance is measured in a broad group of migraineurs to determine whether the existence of such visual field deficits is dependent on the presence of visual aura, is correlated with the duration of migraine history, or frequency of attacks. Twenty-eight migraine with aura, 25 migraine without aura, and 24 non-headache control subjects participated. The performance of the migraine groups was not significantly different from each other. The migraine groups showed significantly lower general sensitivity across the visual field and higher incidence of localized visual field deficits relative to controls. Both length of migraine history and frequency of migraine occurrence over the past 12 months were significantly correlated with lower general sensitivity to flickering visual stimuli.
Publisher: Elsevier BV
Date: 02-2001
DOI: 10.1016/S0042-6989(00)00276-5
Abstract: Both electro-physiological and psychophysical studies point to the existence of detectors specialised for the analysis of optic flow. However, it is unclear whether these detectors are tuned to specific 'cardinal directions' (such as radial and circular motion), or whether they respond equally to all directions of optic-flow motion, including intermediate spiral motions. Here summation and masking studies of motion coherence sensitivity are reported that suggest that optic flow may be tuned to radial and circular cardinal directions. Strong summation was found between two orthogonal directions of spiral motion, but much weaker summation between radial and circular motion. As orthogonal spiral motions always contain a common radial or circular component, the stronger summation for these motions implies that detectors are tuned to radial and circular directions. Similarly, the most effective masking stimuli (placed adjacent to but not superimposed on the test stimuli) tended to be those in the radial or circular directions, even for spiral targets, further suggesting that flow-field motion is detected and discriminated by mechanisms tuned to these 'cardinal' directions.
Publisher: Elsevier BV
Date: 10-1998
DOI: 10.1016/S0042-6989(98)00018-2
Abstract: The ability of observers to discriminate differences in global-motion-signal strength (that is the proportion of coherently moving dots in a field of randomly moving dots) was determined for both first and second-order stimuli. Observers could accurately discriminate differences in signal intensity for all reference signal levels tested 20-100%. A similar pattern of performance was obtained for both types of stimuli. The observed first-order signal-discrimination performance is compatible with the results of electrophysiological studies that have investigated the dependence of the firing rate of V5 cells (also called the middle temporal area) upon global-motion signal intensity.
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 31-03-2015
DOI: 10.1167/15.3.21
Abstract: Shape is a critical cue to object identity. In psychophysical studies, radial frequency (RF) patterns, paths deformed from circular by a sinusoidal modulation of radius, have proved valuable stimuli for the demonstration of global integration of local shape information. Models of the mechanism of integration have focused on the periodicity in measures of curvature on the pattern, despite the fact that other properties covary. We show that patterns defined by rectified sinusoidal modulation also exhibit global integration and are indistinguishable from conventional RF patterns at their thresholds for detection, demonstrating some indifference to the modulating function. Further, irregular patterns incorporating four different frequencies of modulation are globally integrated, indicating that uniform periodicity is not critical. Irregular patterns can be handed in the sense that mirror images cannot be superimposed. We show that mirror images of the same irregular pattern could not be discriminated near their thresholds for detection. The same irregular pattern and a pattern with four cycles of a constant frequency of modulation completing 2π radians were, however, perfectly discriminated, demonstrating the existence of discrete representations of these patterns by which they are discriminated. It has previously been shown that RF patterns of different frequencies are perfectly discriminated but that patterns with the same frequency but different numbers of cycles of modulation were not. We conclude that such patterns are identified, near threshold, by the set of angles subtended at the center of the pattern by adjacent points of maximum convex curvature.
Publisher: SAGE Publications
Date: 07-11-2017
Abstract: Several visual tasks have been proposed as indirect assays of the balance between cortical inhibition and excitation in migraine. This study aimed to determine whether daily measurement of performance on such tasks can reveal perceptual changes in the build up to migraine events. Visual performance was measured daily at home in 16 non-headache controls and 18 in iduals with migraine using a testing protocol on a portable tablet device. Observers performed two tasks: luminance increment detection in spatial luminance noise and centre surround contrast suppression. Luminance thresholds were reduced in migraine compared to control groups ( p 0.05), but thresholds did not alter across the migraine cycle while headache-free, centre-surround contrast suppression was stronger for the migraine group relative to controls ( p 0.05). Surround suppression weakened at around 48 hours prior to a migraine attack and strengthened to approach their headache-free levels by 24 hours post-migraine (main effect of timing, p 0.05). Daily portable testing of vision enabled insight into perceptual performance in the lead up to migraine events, a time point that is typically difficult to capture experimentally. Perceptual surround suppression of contrast fluctuates during the migraine cycle, supporting the utility of this measure as an indirect, non-invasive assay of the balance between cortical inhibition and excitation.
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 25-07-2018
DOI: 10.1167/18.7.7
Abstract: There is an ongoing debate over whether there is convincing evidence in support of global contour integration in shape discrimination tasks, particularly when using radial frequency (RF) patterns as stimuli (Baldwin, Schmidtmann, Kingdom, & Hess, 2016). The objection lies in the previous use of high-threshold theory (HTT), rather than signal detection theory (SDT) to model the probability summation estimates of observer thresholds to determine whether integration of information is occurring around the contour. Here we used a discrimination at threshold method to establish evidence of global processing of two frequently used RF patterns (RF3 and RF5) that does not require mathematical modeling. To provide a bridge between current and past research we examined the two proposed methods, finding that HTT produced probability summation estimates that were more conservative than SDT (when an appropriate number of channels was used to generate estimates). We found no difference in observer thresholds when an RF pattern was presented as the only test stimulus in a block of trials or when two RF patterns were interleaved, and no evidence for a decrease in psychometric slopes with increasing numbers of stimulus elements. These findings are contrary to what is predicted by SDT for a stimulus whose detection conforms to probability summation. Therefore, our results find no evidence that supports probability summation, further demonstrating the importance of using random phase RF patterns while measuring integration around a contour and providing strong evidence for global shape processing around low frequency RF patterns.
Publisher: Public Library of Science (PLoS)
Date: 10-02-2016
Publisher: SAGE Publications
Date: 10-1990
DOI: 10.1068/P190617
Abstract: The role of low-spatial-frequency information in the processing of global stimuli made up of local elements was examined. After selective removal of low spatial frequencies two major changes occurred in the pattern of results. First, response times to global stimuli were significantly slower and the usual speed advantage of global over local processing was lost. Second, when processing local features the usual decrease in response speed when the local and global letters are not the same (consistency effect) was not obtained. These effects could not be explained by changes in error rate, by contrast variation resulting from the process of filtering, or by loss of visual sensitivity due to greater eccentricity of global images.
Publisher: Frontiers Media SA
Date: 12-07-2018
Publisher: MyJove Corporation
Date: 04-12-2013
DOI: 10.3791/50877
Publisher: Elsevier BV
Date: 1987
DOI: 10.1016/0042-6989(87)90076-9
Abstract: Sensitivity to the sudden displacement (phase shift) of a single monocularly presented sinusoidal grating is increased when a static grating of similar spatial frequency is presented to the same eye. If the static grating is presented to the other eye instead sensitivity is, at best, halved. This demonstration implies that monocular and binocular visual pathways differ in their sensitivity to spatial variations of contrast. In addition it provides another ex le in which the monocular visual pathways are more sensitive to spatial displacements than the binocular pathways.
Publisher: Optica Publishing Group
Date: 1995
Abstract: It is now clear that models of positional coding for elements sufficiently separated to permit in idual identification require not only a first stage of linear filtering but also a second stage of representation that is preceded by a rectifying type of nonlinearity. To address the issue of the metric of this second stage we measure separation discrimination for Gabor stimuli of different sizes and of different peak spatial frequencies and separation, with and without different types of lateral distractors. Our results show that there is only a weak dependence of separation discrimination on the spatial frequency of equidetectable, spatially narrow-band stimuli however, carrier spatial frequency can affect the influence that lateral distractors have on separation judgments. We conclude that (1) the second-stage representation is a space-size one consistent with the fact that there are scaled distributions of energy detectors of different sizes and (2) the influence of distractor elements suggests a spatial-frequency influence either at the second-stage representation or at a site beyond this second stage.
Publisher: The Optical Society
Date: 06-1994
Abstract: Psychophysical detection and direction discrimination thresholds for 1c/o, 1-Hz Gabors are plotted in a Weberian long-middle-wavelength-sensitive cone contrast plane. The shape of these threshold contours suggests linear cone contributions to additive (delta L/Lb + delta M/Mb) and opponent (delta L/Lb - delta M/Mb) postreceptoral mechanisms. The opponent mechanism dominates thresholds at the fovea, but sensitivity decreases rapidly with eccentricity in comparison with the additive mechanism. Cone contributions to the mechanisms vary in a small and nonsystematic manner across the retina. The experiments show that the additive mechanism is directionally sensitive at detection threshold. At all eccentricities studied (0-24 degrees), 0.3-log-unit suprathreshold contrasts are necessary for the opponent mechanism to signal direction of motion.
Publisher: Elsevier BV
Date: 12-2010
DOI: 10.1016/J.NEUROPSYCHOLOGIA.2010.10.009
Abstract: The Embedded Figures Test (EFT) requires detecting a shape within a complex background and in iduals with autism or high Autism-spectrum Quotient (AQ) scores are faster and more accurate on this task than controls. This research aimed to uncover the visual processes producing this difference. Previously we developed a search task using radial frequency (RF) patterns with controllable amounts of target/distracter overlap on which high AQ participants showed more efficient search than low AQ observers. The current study extended the design of this search task by adding two lines which traverse the display on random paths sometimes intersecting target/distracters, other times passing between them. As with the EFT, these lines segment and group the display in ways that are task irrelevant. We tested two new groups of observers and found that while RF search was slowed by the addition of segmenting lines for both groups, the high AQ group retained a consistent search advantage (reflected in a shallower gradient for reaction time as a function of set size) over the low AQ group. Further, the high AQ group were significantly faster and more accurate on the EFT compared to the low AQ group. That is, the results from the present RF search task demonstrate that segmentation and grouping created by intersecting lines does not further differentiate the groups and is therefore unlikely to be a critical factor underlying the EFT performance difference. However, once again, we found that superior EFT performance was associated with shallower gradients on the RF search task.
Publisher: Elsevier BV
Date: 06-1998
DOI: 10.1016/S0042-6989(97)00353-2
Abstract: Several experiments were conducted to investigate the role of speed in global-motion processing the extraction of the direction of motion of a small subset of coherently-moving (signal) dots in a stimulus in which the other (noise) dots move in random directions. The specific aim of the experiments was to determine whether multiple speed-tuned global-motion systems exist. The results of these experiments are: (1) when the signal dots were chosen from a group of dots moving at 1.2 degrees s-1, the speed of additional-noise dots had to be below 4.8 degrees s-1 for them to affect global-motion extraction (2) the addition of static dots did not impair the extraction of a global-motion signal carried by dots moving at 1.2 degrees s-1 (3) noise dots moving at 1.2 degrees s-1 impaired the extraction of a global-motion signal from dots moving at 10.8 degrees s-1, though not to the same extent as dots moving at a higher speed and (4) these results were dependent upon speed, not spatial-step size or luminance contrast. These results are interpreted as indicating that global-motion extraction occurs within at least two independent speed tuned systems. One of these systems is sensitive to high speeds and the other to low speeds.
Publisher: Public Library of Science (PLoS)
Date: 11-04-2011
Publisher: Elsevier BV
Date: 04-1992
DOI: 10.1016/0042-6989(92)90186-M
Abstract: The sum of two differently orientated moving sinusoidal gratings of similar spatial frequency, contrast, and velocity appears as a single coherent "plaid" pattern. The visual system is thought to analyse the motion of plaids in two stages, first analysing the motion of the (1-D) components, and then calculating a speed and direction which is consistent with those 1-D motions. We studied the apparent direction of motion of plaids made by adding two components that had the same spatial frequency and contrast, and were symmetrically oriented about the vertical axis. The gratings moved in jumps, and we studied the effect of varying the size of the jump, the angle between the component gratings, and the temporal interval between the jumps, on the perceived direction of motion. When the size of the jumps was increased to 3/8 of their spatial period, the perceived direction of motion of the plaid pattern reversed, although if one component were presented alone, its direction of movement did not reverse. Reversed motion of this type was consistently obtained if the angle between the components was greater than about 140 degrees, if the interval between jumps was at least 25 msec, and if the spatial frequency of the component gratings was less than about 4 c/deg. When the angle between the components was smaller, or the time between jumps was greater, most observers saw normal motion in the direction predicted by the two-stage hypothesis. When the spatial frequency was raised, observers saw no consistent motion.(ABSTRACT TRUNCATED AT 250 WORDS)
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 20-11-2013
DOI: 10.1167/13.13.20
Abstract: Transformational apparent motion (TAM) is a visual phenomenon highlighting the utility of form information in motion processing. In TAM, smooth apparent motion is perceived when shapes in certain spatiotemporal arrangements change. It has been argued that TAM relies on a separate high-level form-motion system. Few studies have, however, systematically examined how TAM relates to conventional low-level motion-energy systems. To this end, we report a series of experiments showing that, like conventional motion stimuli, multiple TAM signals can combine into a global motion percept. We show that, contrary to previous claims, TAM does not require selective attention, and instead, multiple TAM signals can be simultaneously combined with coherence thresholds reflecting integration across the entire stimulus area. This system is relatively weak, less tolerant to noise, and easily overridden when motion energy cues are sufficiently strong. We conclude that TAM arises from high-level form-motion information that enters the motion system by, at least, the stage of global motion pooling.
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 03-2009
DOI: 10.1167/IOVS.08-2517
Abstract: To examine the spatial summation properties for the magnocellular (M) and parvocellular (P) visual pathways in participants with glaucoma and approximately age-matched controls in central and midperipheral retinal eccentricities. Contrast discrimination thresholds were measured for six different stimulus array sizes, using steady- and pulsed-pedestal paradigms designed to measure function of the M and P pathways, respectively. This study involved 15 participants with glaucoma and 17 approximately age-matched controls. All participants completed trials foveally and at 12.5 degrees eccentricity. The peripheral stimulus location for each glaucoma participant was within a quadrant of early visual field loss, and locations were matched for the control group. The glaucoma group demonstrated significantly elevated thresholds compared with the control group (F((1,30)) = 16.29 P < 0.001). Thresholds were also significantly dependent on the stimulus sizes, testing location, and pedestal condition. Data obtained for the steady-pedestal paradigm were fit with an exponential decay function, whereas the pulsed-pedestal data were fit with a linear function, demonstrating different spatial summation properties for the M and P pathways, consistent with previous studies using this methodology. Analyses of the curve parameters obtained from the curve fits indicated no significant difference in the shape of the curves between glaucoma and control participants. Although spatial summation properties are different for presumed M- and P-mediated pathways, the underlying spatial summation properties associated with these pathways are similar in the control and glaucoma participants in this study, centrally and midperipherally.
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 04-01-2023
DOI: 10.1167/JOV.23.1.4
Publisher: Elsevier BV
Date: 11-2021
DOI: 10.1016/J.VISRES.2021.07.009
Abstract: Symmetry perception in dot patterns is tolerant to temporal delays of up to 60 ms within and between element pairs. However, it is not known how factors effecting symmetry discrimination in static patterns might affect temporal integration in dynamic patterns. One such feature is luminance polarity. Using dynamic stimuli with increasing temporal delay (SOA) between the onset of the first and second element in a symmetric pair, we investigated how four different luminance-polarity conditions affected the temporal integration of symmetric patterns. All four luminance polarity conditions showed similar upper temporal limits of approximately 60 ms. However psychophysical performance over all delay durations showed significantly higher symmetry thresholds for unmatched-polarity patterns at short delays, but also significantly less sensitivity to increasing temporal delay relative to matched-polarity patterns. These varying temporal windows are consistent with the involvement of a fast, sensitive first-order mechanism for matched-polarity patterns, and a slower, more robust second-order mechanism for unmatched-polarity patterns. Temporal integration windows for unmatched-polarity patterns were not consistent with performance expected from attentional mechanisms alone, and instead supports the involvement of second-order mechanisms that combines information from ON and OFF channels.
Publisher: Public Library of Science (PLoS)
Date: 10-07-2019
Publisher: Elsevier BV
Date: 11-2007
DOI: 10.1016/J.VISRES.2007.08.016
Abstract: Evidence from summation near threshold psychophysical experiments using compound Glass patterns is presented which supports the existence of mechanisms in the human visual system tuned for coherence in radial and concentric, and +45 degrees and -45 degrees spiral orientations. It is suggested that sensitivity to +45 degrees and -45 degrees logarithmic spirals serves to disambiguate the sense of spiral form, which would not be uniquely specified by measures of the components of orientation along the radial and concentric directions alone. A spiral space is introduced within which radial and concentric patterns are diametrically opposed on one axis and spirals of +45 degrees and -45 degrees on an orthogonal axis and it is proposed that these represent cardinal axes for detecting global structure. Comparison of the sensitivity tuning functions of the four mechanisms tuned to these axes with sensitivity to simple spiral Glass patterns shows that weighted combinations of output from adjacent pairs of this set of mechanisms are sufficient to account for absolute sensitivity to logarithmic spiral Glass patterns of all intermediate spiral angles. Control experiments demonstrate that the combinations are labeled for spiral sense (simple spirals of -22.5 degrees spiral angle can be discriminated from +22.5 degrees spirals at threshold for detection) and that adaptation transfers across quadrants of spiral space (adaptation to spirals of -22.5 degrees results in a decrease in sensitivity to orthogonal +22.5 degrees and -67.5 degrees spirals). Together these observations suggest that sensitivity to spirals in each of the quadrants of spiral space is due to higher order mechanisms reliant on output from 0 degrees , 90 degrees , +45 degrees and -45 degrees cardinal mechanisms.
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 24-04-2018
DOI: 10.1167/18.4.20
Abstract: This study investigated contrast summation over area for moving targets applied to a fixed-size contrast pedestal-a technique originally developed by Meese and Summers (2007) to demonstrate strong spatial summation of contrast for static patterns at suprathreshold contrast levels. Target contrast increments (drifting gratings) were applied to either the entire 20% contrast pedestal (a full fixed-size drifting grating), or in the configuration of a checkerboard pattern in which the target increment was applied to every alternate check region. These checked stimuli are known as "Battenberg patterns" and the sizes of the checks were varied (within a fixed overall area), across conditions, to measure summation behavior. Results showed that sensitivity to an increment covering the full pedestal was significantly higher than that for the Battenberg patterns (areal summation). Two observers showed strong summation across all check sizes (0.71°-3.33°), and for two other observers the summation ratio dropped to levels consistent with probability summation once check size reached 2.00°. Therefore, areal summation with moving targets does operate at high contrast, and is subserved by relatively large receptive fields covering a square area extending up to at least 3.33° × 3.33° for some observers. Previous studies in which the spatial structure of the pedestal and target covaried were unable to demonstrate spatial summation, potentially due to increasing amounts of suppression from gain-control mechanisms which increases as pedestal size increases. This study shows that when this is controlled, by keeping the pedestal the same across all conditions, extensive summation can be demonstrated.
Publisher: Elsevier BV
Date: 05-2016
DOI: 10.1016/J.PSYCHRES.2016.03.046
Abstract: Negative treatment from others is related to elevated levels of trait schizotypy, signifying increased risk for psychosis, but associations with helpful behaviour have been much less studied. Using the Stereotype Content Model we tested the hypothesis that passive and active forms of help would be associated with increased and decreased expression of schizotypy, respectively. Schizotypal traits were assessed in students (N=631) using positive (Perceptual Aberration) and negative (Social Anhedonia) subscales of the Wisconsin Schizotypy Scales-Brief. Experiences of active (intentional) and passive (less deliberative) harm and help were assessed with the Behaviour from Intergroup Affect and Stereotypes Treatment Scale. As predicted, the results showed that experiences of passive help from others were associated with a 2-3 fold increase in scores on schizotypy scales, whilst reports of active help tended to be associated with a decrease in scores on these scales. Results also showed that increased reports of active and passive harm were associated with elevated scores on negative and positive schizotypy subscales, consistent with prior research. These findings, bridging research on social stereotyping and schizotypal personality, challenge the assumption that helpful behaviour from others is always beneficial for in iduals with schizotypal traits who are at increased risk for psychosis.
Publisher: SAGE Publications
Date: 18-07-2011
Abstract: Aim: This study aimed to revisit previous findings of superior processing of motion direction in migraineurs with a more stringent direction discrimination task and to investigate whether increased internal noise can account for motion processing deficits in migraineurs. Methods: Groups of 13 migraineurs (4 with aura, 9 without aura) and 15 headache-free controls completed three psychophysical tasks: one detecting coherence in a motion stimulus, one discriminating the spiral angle in a glass pattern and another discriminating the spiral angle in a global-motion task. Internal noise estimates were obtained for all tasks using an N-pass method. Results: Consistent with previous research, migraineurs had higher motion coherence thresholds than controls. However, there were no significant performance differences on the spiral global-motion and global-form tasks. There was no significant group difference in internal noise estimates associated with any of the tasks. Conclusions: The results from this study suggest that variation in internal noise levels is not the mechanism driving motion coherence threshold differences in migraine. Rather, we argue that motion processing deficits may result from cortical changes leading to less efficient extraction of global-motion signals from noise.
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 04-2004
DOI: 10.1167/IOVS.03-0936
Abstract: To determine whether perimetric performance is worse the day after a migraine than prior interictal measurements, and if so, to determine whether differences have resolved by 1 week after migraine. Twenty-two nonheadache control subjects (aged 18-45 years) and 22 migraineurs (aged 18-45 years: 10 migraine with visual aura, 12 migraine without aura) participated. Standard automated perimetry (SAP) and temporal modulation perimetry (TMP) were measured by perimeter (model M-700 Medmont, Pty Ltd., Camberwell, Victoria, Australia). Control subjects attended two test visits: baseline and retest. Migraineurs attended three times: baseline (>or=4 days after migraine), the day after the offset of the next migraine, and 7 days later. Groups were compared using the global indices of the perimeter: Average Defect (AD) and Pattern Defect (PD), in addition to point-wise comparisons. Group migraineur TMP performance was significantly worse the day after a migraine, showing decreased general sensitivity and increased localized loss. Performance measured 7 days later was not significantly different from that measured the day after a migraine. Group migraineur SAP performance was not significantly worse after migraine however, a subgroup of six eyes from five patients had 10 or more visual field locations with decreases in sensitivity greater than control test-retest 95% confidence limits. Decreased visual field performance was present after migraine, as well as greater test-retest variability in the migraine group compared with control subjects. As migraineurs constitute 10% to 15% of the general population, the presence of this subgroup of patients with periodic prolonged decreased visual field sensitivity after migraine has implications for differential clinical diagnosis, and for clinical research using perimetry.
Publisher: Elsevier BV
Date: 2006
DOI: 10.1016/J.VISRES.2005.09.014
Abstract: Previous studies have identified anomalies of cortical visual processing in migraineurs that appear to extend beyond V1. Migraineurs respond differently than controls to transcranial magnetic stimulation of V5, and can demonstrate impairments of global motion processing. This study was designed to assess the integrity of intermediate stages of both motion and form processing in people with migraine. We measured the ability to integrate local orientation information into a global form percept, and to integrate local motion information into a global motion percept. Control subjects performed significantly better than migraineurs on both tasks, suggesting a diffuse visual cortical processing anomaly in migraine.
Publisher: Elsevier BV
Date: 08-1996
DOI: 10.1016/0042-6989(95)00304-5
Abstract: A global dot-motion stimulus was employed in order to investigate the interaction between luminance and chromatic signals in motion processing. Thresholds are determined by measuring the minimum number of dots which need to move in a coherent fashion in a field of randomly moving dots in order for the observers to be able to determine the direction of coherent motion. We found that: (1) observers could not track an achromatic signal-dot which changes its luminance polarity between frame transitions. The addition of a consistent chromatic signal allowed observers to track such a dot when the dot contained low- (8%) luminance contrast but this ability was impaired as the luminance contrast was increased (2) the addition of chromatic contrast to a dot which contained consistent low-luminance contrast could result in threshold elevation. For fixed contrast chromatic and luminance signals, the presence and degree of threshold elevation depended upon the spatiotemporal properties of the dot motion (3) the ability of observers to extract a global-motion signal carried by a group of dots of one colour was impaired by the addition of a number of additional-noise dots of a different colour. These results are interpreted as indicating that: (1) the motion-selective cells that are sensitive to chromatic signals are also sensitive to luminance signals (2) the combined chromatic and luminance and purely luminance motion cells are pooled to form a single pathway prior to global-motion extraction and (3) the negative interaction observed between the chromatic and luminance signals is likely to be due to the differences in the processing speeds of the combined luminance and chromatic and the purely luminance sensitive motion cells.
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 06-2004
DOI: 10.1167/IOVS.03-1225
Abstract: It is well established that contrast sensitivity is reduced in glaucoma. This study explored whether such contrast processing abnormalities consist of an absolute threshold level difference or a problem with contrast gain control. Seventeen patients with primary open-angle glaucoma and 17 approximately age-matched control subjects participated. Subjects were tested foveally and midperipherally (12.5 degrees ). Subjects with glaucoma were tested in a peripheral region of relatively normal visual field (neighboring locations required to be within the normal 95% confidence limit on the total deviation plot of their most recent SITA/full threshold Humphrey Field Analyzer assessment Carl Zeiss Meditec, Dublin, CA). Control subjects were tested in matching locations. Contrast discrimination was assessed using the steady-pedestal (magnocellular [M] pathway) and pulsed-pedestal (parvocellular [P] pathway) stimuli of Pokorny and Smith for seven pedestal luminances between 15 and 75 cd/m(2), presented on a background of 30 cd/m(2). Glaucoma group thresholds were significantly elevated compared with control subjects foveally and peripherally on both the pulsed-pedestal (P) and steady-pedestal (M) tasks (P < 0.01). Effect size statistics revealed slightly greater deficits on the P pathway task and greater deficits for pedestals that were decrements, rather than increments, from the surround luminance. Foveal deficits were of a magnitude to be explained by a reduction in contrast sensitivity however, the peripheral deficits were greater than predicted by this factor alone. Foveal and midperipheral dysfunction of both M and P pathways was identified in people with glaucoma, in areas of relatively normal visual field performance. These findings are supportive of nonselective neural adaptation abnormalities in early glaucoma.
Publisher: Elsevier BV
Date: 09-2008
DOI: 10.1016/J.VISRES.2008.07.003
Abstract: The study of shape processing in the human visual system has frequently employed radial frequency (RF) patterns as conveniently manipulable stimuli. This study uses an adaptation paradigm to investigate how local shape information is s led in the processing of RF contour shapes. Experiment 1 measured thresholds for detecting a fixed mean radius RF contour following adaptation to RF patterns which, in separate conditions, varied in mean radius and radial frequency. Results reveal that, adaptation is strongly tuned for RF over a range of pattern radii, but is not tuned for the number of cycles of radial modulation per visual degree of contour length a characteristic that changes with both radius and radial frequency. Experiment 2 manipulated the polar angle separation on the fronto-parallel plane between curvature features on a fixed RF by foreshortening the pattern appearance (consistent with a rotation in depth) and shows that RF shape processing is tuned for fronto-parallel separation angles between curvature features. Results were near identical when a stereo rotation cue was added to the perspective modified RF. In the second part of Experiment 2 we showed that RF shape adaptation is also tuned for the polar angular extent of the curvature represented by the lobe at that angle. Collectively, our results indicate that the polar angle at which local curvature features appear, in addition to the angular extent of the curvature feature at that location, are both critical parameters for coding specific RF shapes.
Publisher: Elsevier BV
Date: 2020
DOI: 10.1016/J.VISRES.2019.11.005
Abstract: Objects are often identified by the shape of their profiles but complex objects are often comprised of multiple articulated components. It has been proposed that complex objects are decomposed and recognized by their component parts. This study exploits the proposition that the visual system decomposes objects at matched deep concavities on their boundaries. Rapid decreases in thresholds for detection of sinusoidal deformation of a circle's radius with number of cycles of modulation shows that shape information is integrated around radial frequency (RF) patterns. Here we merge RF patterns to form composite patterns with concavities and show that integration around the RF patterns is disrupted if the concavities are shallow but preserved if they are deep, consistent with their decomposition at matched deep concavities. Geon theory identifies complex patterns through a structural description of viewpoint invariant primitives known as geons. Geons are defined by properties on their boundaries that co-occur in a non-accidental manner across viewpoint changes rather than by reconciling metric properties such as curvature with viewpoint specific templates. Similarly, shapes of RF patterns are defined by the positions of curvature features on their boundaries. We argue that RF patterns provide flexible stimuli that might be used to study geons.
Publisher: Elsevier BV
Date: 1985
DOI: 10.1016/0042-6989(85)90040-9
Abstract: Observers were asked to detect the direction of displacement of a 30 c/deg grating. They were virtually unable to perform this task when the component was presented alone but when either a 28 or a 32 c/deg component (neither of which moved) was added to the 30 c/deg component observers were extremely sensitive to displacements of the 30 c/deg component. These results suggest that the detection of displacements cannot take place within narrow-band spatial channels, but relies on a mechanism which compares the output of channels in different spatial positions.
Publisher: Optica Publishing Group
Date: 02-1994
Publisher: Springer Science and Business Media LLC
Date: 02-1990
DOI: 10.1038/343554A0
Abstract: Human eyes are in constant and rapid motion even when observers try to maintain steady fixation. Also, the visual system has a sluggish temporal response. In combination, these two factors would be expected to blur stimuli and reduce spatial sensitivity. But observers are able to detect a difference in separation of a few seconds of arc between two closely spaced parallel lines. Here we report that even very large amounts of positional jitter of the line pair has minimal impact on this ability. This result is in marked contrast to the deterioration observed when targets are swept linearly across the retina, but is consistent with a system that must ignore oculomotor jitter. To explain these results will require a re-evaluation of current models of position coding in human vision.
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 25-11-2015
DOI: 10.1167/15.15.19
Abstract: Traditional theories of visual perception have focused on either form or motion processing, implying a functional separation. However, increasing evidence indicates that these features interact at early stages of visual processing. The current study examined a well-known form-motion interaction, where a shape translates along a circular path behind opaque apertures, giving the impression of either independently translating lines (segmentation) or a globally coherent, translating shape. The purpose was to systemically examine how low-level motion information and form information interact to determine which percept is reported. To this end, we used a stimulus with boundaries comprising multiple, spatially-separated Gabor patches with three to eight sides. Results showed that shapes with four or fewer sides appeared to move in a segmented manner, whereas those with more sides were integrated as a solid shape. The separation between directions, rather than the total number of sides, causes this switch between integrated or segmented percepts. We conclude that the change between integration and segmentation depends on whether local motion directions can be independently resolved. We also reconcile previous results on the influence of shape closure on motion integration: Shapes that form open contours cause segmentation, but with no corresponding enhanced sensitivity for shapes forming closed contours. Overall, our results suggest that the resolution of the local motion signal determines whether motion segmentation or integration is perceived with only a small overall influence of form.
Publisher: Optica Publishing Group
Date: 05-2000
Abstract: The background modulation method has been proposed as a useful test of early visual mechanisms [Biol. Cybern. 37, 77 (1980) Biol. Cybern. 47, 173 (1983)]. The task involves measuring detection thresholds for a luminous spot (increment) drifting over a spatially or temporally modulated background. The study explores the nature of the detecting mechanism in terms of spatial and temporal filters for both spatial and temporal background modulations. In both cases we find that thresholds can be explained by spatial contrast cues generated by the moving spot and that their spatiotemporal characteristics suggest detection by magnocellular processes.
Publisher: Wiley
Date: 05-1998
DOI: 10.1111/J.1442-9071.1998.TB01356.X
Abstract: Data is reported from an ongoing trial considering whether visual loss associated with migraine is consistent with a selective deficit in M- or P-cell functioning. The psychophysical tests used include spatio-temporal contrast thresholds and luminance increment thresholds for a spot drifting across a spatially or temporally modulated background. A migraineur and 15 non-headache controls participated in the present study. Measurements were made foveally and at 10 degrees in the superior field. Static and flicker perimetry were conducted. Regionalized losses occurred for stimuli with moderate temporal frequencies (16 Hz), which is consistent with M-cell dysfunction.
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 02-2018
DOI: 10.1167/18.2.2
Abstract: Objects are often identified by the shape of their contours. In this study, visual search tasks were used to reveal a visual dimension critical to the analysis of the shape of a boundary-defined area. Points of maximum curvature on closed paths are important for shape coding and it was shown here that target patterns are readily identified among distractors if the angle subtended by adjacent curvature maxima at the target pattern's center differs from that created in the distractors. A search asymmetry, indicated by a difference in performance in the visual search task when the roles of target and distractor patterns are reversed, was found when the critical subtended angle was only present in one of the patterns. Performance for patterns with the same subtended angle but differing local orientation and curvature was poor, demonstrating insensitivity to differences in these local features of the patterns. These results imply that the discrimination of objects by the shape of their boundaries relies on the relative positions of their curvature maxima rather than the local properties of the boundary from which these positions are derived.
Publisher: Elsevier BV
Date: 1991
DOI: 10.1016/0042-6989(91)90049-B
Abstract: Foveal target detection thresholds are elevated by presenting a counterphasing, vertical squarewave grating in the peripheral retina. This psychophysical "shift effect" has been considered to be an analogue of the neurophysiological "periphery effect" first described by McIlwain (1964 Journal of Neurophysiology, 27, 1154-1173). Physiological response properties of cells from the retina and lateral geniculate nucleus of cat and primate visual systems predict that sensitivity thresholds should also be elevated for peripheral targets in the presence of a foveal counterphasing mask. In these experiments, contrast sensitivities for human observers were obtained using a two-interval forced-choice procedure for peripheral target sinusoids in the presence of a foveal counterphasing mask. A suppressive shift effect was elicited by the foveal counterphasing squarewave mask, but only for counterphasing peripheral sinusoids. Masking was only obtained at the lowest spatial frequencies for both the peripheral and foveal shift effects.
Publisher: Frontiers Media SA
Date: 2013
Publisher: Elsevier BV
Date: 1985
DOI: 10.1016/0042-6989(85)90100-2
Abstract: We have used DOG stimuli to selectively stimulate size tuned channels within the visual system in order to investigate the relationship between stereo and vernier acuity. We measured these acuities as a function of spatial frequency, retinal eccentricity and distance from the fixation point in depth. Both hyperacuities are poorer with low spatial frequencies but vernier was effected to a smaller extent. Vernier acuity deteriorated to a much greater degree than stereo acuity as retinal eccentricity increased up to 40 arc min. Stereo acuity was more dependent upon distance from the fixation point in depth than would be expected from the dependence of vernier acuity on retinal eccentricity. We conclude that there must be different limiting factors for the two hyperacuity tasks.
Publisher: Springer Science and Business Media LLC
Date: 26-02-2001
Abstract: The human visual system contains a functional sub-system that is specialized to extract image motion. The sensitivities of neurons change as one moves higher in the pathway. Initially cells collect responses from small retinal areas but later those local signals are combined to extract global motion either frontoparallel or radial motion relative to the center of the visual field. This sequence of processing is conducted in parallel by pathways sensitive to the motion of either the first- or second-order luminance statistics of the image. Previously it had been shown that these two pathways were independent at the level at which local motion signals and frontoparallel global motion signals are extracted. In this study independence is tested during the extraction of radial global motion a process strongly associated with cortical area MST (or V6) and the next logical level in the motion pathway. We find that the two pathways do provide independent estimates of radial motion and are, therefore, independent at all levels of the motion pathway that have been tested to date.
Publisher: Springer Science and Business Media LLC
Date: 04-10-1999
Abstract: In solving the selection-for-action problem, it is believed that attentional mechanisms enable dominance of target over non-target objects. However, under some conditions, information from non-target objects "interferes" with the action to a relevant target. We investigated the possibility that this interference may result when the irrelevant object activates a specific subset of visuomotor pathways. Participants reached to grasp three-dimensional stimuli while actively attending to a nearby flanker object. The means by which the flanker was presented was manipulated. This relevant object was illuminated either abruptly or gradually. The parvocellular pathway in early visual processing is equally activated in both conditions. The magnocellular pathway is strongly activated by abrupt presentation and weakly activated with gradual presentation of the flanker object. Kinematics of the reach-to-grasp action to the target showed signs of interference only in the sudden illumination condition. This suggests a dissociation between dorsal and ventral cortical streams in terms of relevance for action. Our data suggests that this effect is not due to early visual-pathway differences, but instead reveals a property of a transient object-based visual attention mechanism.
Publisher: Wiley
Date: 10-05-2010
DOI: 10.1111/J.1469-7610.2009.02203.X
Abstract: Several researchers have found evidence for impaired global processing in the dorsal visual stream in in iduals with autism spectrum disorders (ASDs). However, support for a similar pattern of visual processing in the ventral visual stream is less consistent. Critical to resolving the inconsistency is the assessment of local and global form processing ability. Within the visual domain, radial frequency (RF) patterns - shapes formed by sinusoidally varying the radius of a circle to add 'bumps' of a certain number to a circle - can be used to examine local and global form perception. Typically developing children and children with an ASD discriminated between circles and RF patterns that are processed either locally (RF24) or globally (RF3). Children with an ASD required greater shape deformation to identify RF3 shapes compared to typically developing children, consistent with difficulty in global processing in the ventral stream. No group difference was observed for RF24 shapes, suggesting intact local ventral-stream processing. These outcomes support the position that a deficit in global visual processing is present in ASDs, consistent with the notion of Weak Central Coherence.
Publisher: Frontiers Media SA
Date: 2013
Publisher: Oxford University Press (OUP)
Date: 11-10-2021
Abstract: Visual snow syndrome is a neurological condition characterized by a persistent visual disturbance, visual snow, in conjunction with additional visual symptoms. Cortical hyperexcitability is a potential pathophysiological mechanism, which could be explained by increased gain in neural responses to visual input. Alternatively, neural noise in the visual pathway could be abnormally elevated. We assessed these two potential competing neural mechanisms in our studies of visual contrast perception. Cortical hyperexcitation also occurs in migraine, which commonly co-occurs with visual snow syndrome. Therefore, to determine whether the effect of visual snow syndrome can be distinguished from interictal migraine, we recruited four participant groups: controls, migraine alone, visual snow syndrome alone and visual snow syndrome with migraine. In the first experiment, we estimated internal noise in 20 controls, 21 migraine participants and 32 visual snow syndrome participants (16 with migraine) using a luminance increment detection task. In the second experiment, we estimated neural contrast gain in 21 controls, 22 migraine participants and 35 visual snow syndrome participants (16 with migraine) using tasks assessing sensitivity to changes in contrast from a reference. Contrast gain and sensitivity were measured for the putative parvocellular and ‘on' and ‘off' magnocellular pathways, respectively. We found that luminance increment thresholds and internal noise estimates were normal in both visual snow syndrome and migraine. Contrast gain measures for putative parvocellular processing and contrast sensitivity for putative off magnocellular processing were abnormally increased in visual snow syndrome, regardless of migraine status. Therefore, our results indicate that visual snow syndrome is characterized by increased neural contrast gain but not abnormal neural noise within the targeted pathways.
Publisher: Elsevier BV
Date: 09-1993
DOI: 10.1016/0042-6989(93)90169-W
Abstract: We measured the ability of human observers to discriminate the direction of motion of different spatial patterns presented for durations ranging from 0.021 to 0.67 sec. The patterns were: (1) a vertical grating (spatial frequency 0.93 c/deg at 5% contrast) (2) a "beat" pattern made by adding vertical gratings of 6.3 and 5.4 c/deg both at 5% contrast moving in opposite directions (this pattern appears as a horizontally moving, 0.93 c/deg "beat" i.e. spatial variation in the contrast of a stationary vertical grating of 5.8 c/deg) and (3) a "plaid" pattern made by adding gratings of 5.9 c/deg orientated +/- 81 deg from vertical (this pattern can also be expressed as a horizontally moving 1.9 c/deg beat in a horizontal grating of 5.8 c/deg). The direction of motion of the grating and the plaid pattern were discriminable at all durations tested. The direction of motion of the beat could only be discriminated at durations above approx. 200 msec. We suggest that this is a consequence of the fact that the moving beat is only visible to second-order mechanisms, and that second-order mechanisms for the analysis of motion operate more slowly than first-order mechanisms.
Publisher: SAGE Publications
Date: 09-1993
DOI: 10.1068/P221013
Abstract: It is reasonable to ask whether observers are more sensitive to the pattern of image motion caused by forward locomotion through the environment than to the pattern caused by backward locomotion. The distribution of sensitivities of cells in MT does show such a bias, although this bias is minimal at small eccentricities. Additionally, both locomotion-induced stimulation and the sensitivities of MT cells suggest greater sensitivity should be obtained in the lower visual field. Previous research on this issue has usually employed frontoparallel motion in patterns presented to one side of the fixation point. Both centrifugal and centripetal biases have been obtained. In this study the stimuli present motion signals that travel radially from (or towards) the fixation point. These stimuli, which produce a strong percept of motion in depth, are an adaptation of the global-dot-motion stimulus employed by Newsome and Pare. With these stimuli we find that sensitivity to motion in depth is greater in the lower visual field than in the upper visual field, and that sensitivity is greater to centripetal motion than to either centrifugal or frontoparallel motion. This centrifugal bias in sensitivity decreases with eccentricity. The last two findings contradict the notion that the bias is produced by the visual experience induced by normal forward locomotion and also that the detection of motion in depth is subserved by MT.
Publisher: Elsevier BV
Date: 09-2008
DOI: 10.1016/J.VISRES.2008.07.015
Abstract: Radial frequency (RF) contours can be used to represent the boundaries of natural objects, making them a useful stimulus with which to study shape processing. The current study used these contours to investigate whether luminance- and contrast-defined shape cues are combined in the detection of globally processed contours. A set of three experiments are presented. Experiment 1 shows that an RF contour defined by any one of positive or negative luminance contrast relative to background or second-order texture (contrast defined), is detected in accordance with a global pooling of local shape information. Experiment 2 uses a lateral masking paradigm to reveal interactions between global shapes defined by luminance of either polarity or a second-order contrast variation. Experiment 3 shows that an RF pattern defined by all three characteristics (positive, negative luminance polarity and contrast modulation) in nonoverlapping contour sections can still be assembled into a global shape. These findings indicate that at the level where RF contours are globally processed, luminance of either polarity- or contrast-defined shape information can be effectively combined.
Publisher: Elsevier BV
Date: 04-2009
DOI: 10.1016/J.VISRES.2009.01.009
Abstract: The retinal flow of information during locomotion provides cues to instantaneous heading. Reconciliation of observer trajectory with the internal representation of the environment implies that the positions of the centre of structure of global motion can be localized relative to points in the visual field. Humans are also sensitive to global structure in Glass patterns, which can approximate temporally integrated optic flow. Encoding of the position of centre of structure of Glass patterns could augment the motion information. However, Glass-like pattern structure could also be present in the texture of objects and indicate their centres, raising the question of whether the centres of form and motion patterns are encoded separately. Psychophysical methods are used to examine ability to localize the centres of structure of Glass and global dot motion (GDM) patterns. Radial and concentric Glass patterns are localized more precisely than spiral Glass patterns but performance in localizing the centres of radial, concentric and spiral GDM patterns is equally precise. Also, Glass patterns centres can be localized at signal levels close to their threshold for discrimination from wholly incoherent patterns but GDM pattern centres cannot, suggesting that detectors for looming and rotating stimuli exist that do not rely on the provision of a centre of structure. Collectively, our results provide evidence for independent encoding of the positions of the centres of structure of global motion and form patterns. These positions can be accurately and precisely localized within the visual field. While the centres of structure of a number of form patterns can be simultaneously encoded, allowing their positions to be compared, only a single focus of expansion for optic flow is returned.
Publisher: SAGE Publications
Date: 15-12-2012
Abstract: Aim: Increased contrast-level dependent internal noise has been reported in migraine. This study aimed to investigate whether a general increase in internal noise impacted on other tasks thought to assess functioning in cortical area V1 and was evident in global contour coding (V4). Methods: Eleven migraineurs (six with aura) and 12 headache-free controls completed three psychophysical tasks: (i) contrast detection, (ii) discrimination of the angle of a spiral path and (iii) detection of deformation from circularity. Internal noise estimates were obtained using an N-pass method that compared responses to repeated presentations of identical stimuli. Internal noise results in inconsistent responses across different runs. Results: Migraineurs had significantly higher contrast thresholds when there was high external luminance noise. There were no other significant group differences in thresholds. Increased multiplicative noise associated with contrast processing was replicated and increased additive noise, which is independent of the visual input, was found for the global form task. Conclusions: This study provides further evidence for increased multiplicative internal noise associated with contrast processing in migraineurs. However there is no generalised increase in internal noise in V1 as noise estimates for angular discrimination were normal. Increased additive internal noise was associated with the global shape task, co-occurring with increased efficiency.
Publisher: SAGE Publications
Date: 11-2016
Publisher: Elsevier BV
Date: 11-2016
DOI: 10.1016/J.NEURON.2016.10.038
Abstract: A proposal for an Australian Brain Initiative (ABI) is under development by members of the Australian Brain Alliance. Here we discuss the goals of the ABI, its areas of research focus, its context in the Australian research setting, and its necessity for ensuring continued success for Australian brain research.
Publisher: SAGE Publications
Date: 08-2006
DOI: 10.1111/J.1468-2982.2006.01154.X
Abstract: Some migraineurs have increased thresholds for the detection of global dot motion. We investigated whether migraineurs show consequential abnormalities in the determination of direction of self-motion (heading) from simulated optic flow. The ability to determine heading from optic flow is likely to be necessary for optimal determination of self-motion through the environment. Twenty-five migraineurs and 25 controls participated. Global dot motion coherence thresholds were assessed, in addition to performance on two simulated heading tasks: one with a symmetrical flow field, and the second with differing velocity of optic flow on the left and right sides of the participant. While some migraineurs demonstrated abnormal global motion coherence thresholds, there was no difference in performance on the heading tasks at either simulated walking (5 km/h) or driving (50 km/h) speeds. Increased global motion coherence thresholds in migraineurs do not result in abnormal judgements of heading from 100± coherent optic flow.
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 03-2009
DOI: 10.1167/9.3.4
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 2010
DOI: 10.1167/10.3.20
Publisher: Elsevier BV
Date: 05-2007
DOI: 10.1016/J.VISRES.2007.01.006
Abstract: Radial frequency (RF) patterns have been used to study the processes involved in shape perception. The psychophysical literature suggests that there are distinct global and local shape detection processes for low and high radial frequency patterns, but this has not been tested in a combined contour pattern, such as would be needed to describe the contours of most natural objects. Here, we combined frequencies from the local and global range onto a compound RF structure. Observers' ability to detect a single RF component on the compound pattern was measured. Results show that sensitivity to high frequency local deviations in shape was not affected by the presence of a globally perceived low frequency pattern. In the reverse condition, detection of global form was not influenced by adding local deviations onto the structure. This suggests that local and global shape information can be detected independently within the human visual system.
Publisher: Elsevier BV
Date: 04-1992
DOI: 10.1016/0042-6989(92)90185-L
Abstract: The sum of two differently orientated moving sinusoidal gratings of similar spatial frequency, contrast, and velocity appears as a single coherent "plaid" pattern. The visual system is thought to analyse the motion of plaids in two stages, first analysing the motion of the (1-D) components, and then calculating a speed and direction which is consistent with those 1-D motions. We find that the direction of motion of a plaid (components 1.6 c/deg orientated +60 degrees and -60 degrees) can be discriminated at velocities so low that the direction of motion of its components is not discriminable. This finding is not consistent with the "two-stage" hypothesis in the form that it is usually expressed. We suggest that mechanisms sensitive to the motion of local elements in the pattern, such as edges, could also contribute to the first stage of the analysis of plaid motion.
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 2003
DOI: 10.1167/IOVS.02-0630
Abstract: To assess contrast-discrimination thresholds in patients with migraine who have manifest visual field loss. This study was undertaken to determine whether contrast processing abnormalities in migraineurs are more readily identified by using stimuli that elicit a response from the subject that depends, at least in part, on adaptation mechanisms, and if so, whether deficits appear more pronounced in magnocellular (M) or parvocellular (P) visual pathways. Ten patients with migraine who had abnormal visual fields measured with flicker perimetry but had normal standard automated perimetry (SAP) thresholds participated, along with 15 age-matched control subjects. Contrast-discrimination performance was assessed with the steady-pedestal (magnocellular) and pulsed-pedestal (parvocellular) stimuli of Pokorny and Smith for seven pedestal luminances between 15 and 60 cd/m(2) on a background of 30 cd/m(2). Subjects were tested foveally and midperipherally at 12.5 degrees. Migraineurs were tested in the quadrant of worst visual field performance. Control subjects were assessed in locations matched to those of the migraine group. Foveal performance was not significantly different between the migraine and control groups for either task. At 12.5 degrees the migraine group had significantly raised thresholds for both conditions. Effect size statistics revealed similar deficit magnitudes for each test (steady pedestal, -1.06 pulsed pedestal, -1.04). Dysfunction in both the M and P pathways was identified in the midperipheral visual field of the migraine group. The P pathway dysfunction was not identified by SAP. These findings support the possibility of nonselective neural adaptation abnormalities in some subjects with migraine.
Publisher: Springer Science and Business Media LLC
Date: 18-04-2009
DOI: 10.1007/S10803-009-0740-5
Abstract: The current research investigated, firstly, whether in iduals with high levels of mild autistic-like traits display a similar profile of embedded figures test (EFT) and global motion performance to that seen in autism. Secondly, whether differences in EFT performance are related to enhanced local processing or reduced global processing in the ventral visual stream was also examined. Results indicated that people who scored high on the Autism-spectrum Quotient (AQ) were faster to identify embedded figures, and had poorer global motion and global form thresholds than low AQ scorers. However, the two groups did not differ on a task assessing lower-level input to the ventral stream. Overall the results indicate that in iduals with high levels of autistic-like traits have difficulties with global integration in the visual pathways, which may at least partly explain their superior EFT performance.
Publisher: Elsevier BV
Date: 10-2014
DOI: 10.1016/J.VISRES.2014.08.015
Abstract: In iduals with autistic traits (measured with Autism-spectrum Quotient, AQ) often excel in detecting shapes hidden within complex structures (e.g. on the Embedded Figures Test, EFT). This facility has been attributed to either weaker global integration of scene elements or enhanced local processing, but 'local' and 'global' have various meanings in the literature. The function of specific global visual mechanisms involved in integrating contours, similar to EFT targets was examined. High AQ scorers produced enhanced performance on the EFT and an alternative Radial Frequency Search Task. Contrary to 'generic' interpretations of weaker global pooling, this group displayed stronger pooling of contour components that was correlated with search ability. This study therefore shows a global contour integration advantage in high AQ observers.
Publisher: American Psychological Association (APA)
Date: 11-2016
DOI: 10.1037/XHP0000257
Abstract: Radial Frequency (RF) patterns are a useful stimulus for assessing sensitivity to changes in shape. With these patterns it is possible to separate sensitivity to local curvature information from the ability to globally integrate information around the contour. Previous work has demonstrated that young, school-age children are less sensitive to deformation in RF patterns than adults. However, since the efficiency of contour integration was not assessed, age-related differences in performance could arise from either changes in the strength of global pooling of information, the sensitivity to local curvature information, or both. In this study, psychophysical methods were used to reassess changes in sensitivity to RF patterns, separating changes in sensitivity to local curvature information from changes in contour integration strength. Typically developing observers (aged 6-24, N = 104) were tested using a 2-alternative forced-choice discrimination task with either 1, 2 or 3 cycles of sinusoidal modulation in a pattern of fixed RF. Thresholds were lower for older observers but the rate of change, as more modulation cycles were added, was approximately constant across age. The results indicate that changes in sensitivity to RF3 patterns across age are due to changes in local curvature sensitivity and not to the strength of contour integration. (PsycINFO Database Record
Publisher: Elsevier BV
Date: 03-2022
DOI: 10.1016/J.VISRES.2021.107975
Abstract: The perceived shapes of almost circular paths are modified by concentrically placed context paths. These induced changes have previously been attributed to curvature masking. This paper shows that, instead, they can be explained by the impacts of local tilt illusions. First, the tilt-illusion was measured over the full range of orientation differences between short test and context lines and it was shown that the resulting function can be predicted by a model based on a vectorial population response of a bank of orientation selective channels, provided lateral inhibition between channels with the same orientation selectivity and adjacent receptive fields was postulated. Subsequently, it was demonstrated that, if the perceived shape of a test path were modified to accommodate the predicted local tilt-illusion, then this could account for previously reported changes in the detectability of a path sinusoidally modulated in radius. Further, we measured points of subjective vertical in test lines and points of subjective circularity in test paths when surrounded by modulated context paths. The tilt required to null the tilt-illusion approximated the maximum orientation difference from circular measured in the modulated paths at their point of subjective circularity, supporting the proposal that the illusory shape change is due to local changes in the position of the path arising from a response to local tilt illusions induced by the orientation context. An important corollary to this result is that such effects will generalize to all paths which are adjacent.
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 05-2003
DOI: 10.1167/3.4.2
Publisher: Elsevier BV
Date: 10-2003
DOI: 10.1016/S0042-6989(03)00403-6
Abstract: Much of our knowledge about motion perception has been obtained by studying bars moving within apertures. When viewed within an ambiguously oriented aperture such as a circle, bars appear to move orthogonal to their orientation. We demonstrate that if the local orientation of the aperture edges is altered, a direction consistent with the edge orientation is seen. Indeed, the perceived direction can be strongly influenced by static lines separated from the edge of the moving stimulus. These results support recent suggestions that precise motion direction is likely to be determined by static orientation cues.
Publisher: Elsevier BV
Date: 2005
DOI: 10.1016/J.NEUROPSYCHOLOGIA.2004.10.003
Abstract: Frith and Happe (Frith, U., & Happe, F. (1994). Autism: Beyond theory of mind. Cognition, 50, 115-132) argue that in iduals with autism exhibit 'weak central coherence': an inability to integrate elements of information into coherent wholes. Some authors have speculated that a high-level impairment might be present in the dorsal visual pathway in autism, and furthermore, that this might account for weak central coherence, at least at the visuospatial level. We assessed the integrity of the dorsal visual pathway in children diagnosed with an autism spectrum disorder (ASD), and in typically developing children, using two visual tasks, one examining functioning at higher levels of the dorsal cortical stream (Global Dot Motion (GDM)), and the other assessing lower-level dorsal stream functioning (Flicker Contrast Sensitivity (FCS)). Central coherence was tested using the Children's Embedded Figures Test (CEFT). Relative to the typically developing children, the children with ASD had shorter CEFT latencies and higher GDM thresholds but equivalent FCS thresholds. Additionally, CEFT latencies were inversely related to GDM thresholds in the ASD group. These outcomes indicate that the elevated global motion thresholds in autism are the result of high-level impairments in dorsal cortical regions. Weak visuospatial coherence in autism may be in the form of abnormal cooperative mechanisms in extra-striate cortical areas, which might contribute to differential performance when processing stimuli as Gestalts, including both dynamic (i.e., global motion perception) and static (i.e., disembedding performance) stimuli.
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 02-09-2021
DOI: 10.1167/JOV.21.10.5
Publisher: Elsevier BV
Date: 1989
DOI: 10.1016/0042-6989(89)90035-7
Abstract: When two sinusoidal gratings of the same orientation and similar spatial frequency are summed, the resulting pattern has a periodic spatial variation or beat in contrast. Although the pattern contains no luminance modulation component at the beat frequency, it behaves in some respects as if it did: human observers for ex le are very good at detecting spatial displacements of the beat. We wished to test the possibility that a non-linearity in the visual system generates a component (a "distortion product") at the beat frequency, and that it is displacement of the distortion product that observers detect. Attempting to "null" the distortion product by adding to the beat pattern a sinusoidal component of the same spatial frequency as the distortion product but 180 deg out of phase with it does not impair performance in detecting motion of the beat there is no nulling at any litude of the added component. Reducing the phase shift of the hypothetical distortion product by adding a static sinusoid to the moving beat pattern fails to produce the predicted fall in performance. These results suggest that distortion products do not contribute to our sensitivity to the displacement of beat patterns. Reversing the contrast of a beat pattern when it is displaced, slightly increases sensitivity to displacement, the same manipulation impairs performance with luminance patterns. This is consistent with the notion that the beat is detected as an unsigned local contrast signal.
Publisher: MyJove Corporation
Date: 21-04-2022
DOI: 10.3791/63699
Abstract: The low cost and availability of Virtual Reality (VR) systems have supported a recent acceleration of research into perception and behavior under more naturalistic, multisensory, and immersive conditions. One area of research that has particularly benefited from the use of VR systems is multisensory integration, for ex le, the integration of visual and vestibular cues to give rise to a sense of self-motion. For this reason, an accessible method for the controlled physical rotation of an observer in a virtual environment represents a useful innovation. This paper presents a method for automating the rotation of an office swivel chair along with a method for integrating that motion into a VR experience. Using an ex le experiment, it is demonstrated that the physical motion, thus produced, is integrated with the visual experience of an observer in a way consistent with expectations high integration when the motion is congruent with the visual stimulus and low integration when the motion is incongruent.
Publisher: Springer Science and Business Media LLC
Date: 24-10-2008
DOI: 10.1007/S10803-008-0658-3
Abstract: Although there is good evidence that the behavioral traits of autism extend in lesser form to the general population, there has been limited investigation of whether cognitive features of the disorder also accompany these milder traits. This study investigated whether the superiority in visuospatial analysis established for in iduals with autism also extends to in iduals in the general population who self-report autistic-like traits. In an initial study, students scoring high on the Autism-spectrum Quotient (AQ) were faster and more accurate on the Embedded Figures Test (EFT) and the Block Design subscale of the Wechsler Intelligence Scale III compared to those scoring low on the AQ. A second study showed that high AQ scorers were faster to complete the EFT compared to low AQ scorers irrespective of IQ. Results are discussed with reference to weak central coherence theory and the autism spectrum.
Publisher: Elsevier BV
Date: 02-2009
DOI: 10.1016/J.VISRES.2008.11.009
Abstract: Geisler's [Geisler, W. S. (1999). Motion streaks provide a spatial code for motion direction. Nature, 400, 65-69] model of motion processing proposes that image smear arising from extended integration periods in Simple cells creates motion streaks which indicate the axis of motion. Orientation cues were provided using textured dot-pairs composed of randomly-placed luminance increments and decrements giving contours with the same average luminance as the background and incompatible with smear. These contours were equally effective in signalling both motion axis and coherence. The results support the assertion that extended contours can determine the perceived axis of motion and that the motion system can use second-order texture cues for this purpose. Inputs of this type are therefore required for both Geisler's (1999) and Barlow and Olshausen's [Barlow, H. B., & Olshausen, B. A. (2004). Convergent evidence for the visual analysis of optic flow through anisotropic attenuation of high spatial frequencies. Journal of Vision, 4, 415-426] models of this ability.
Publisher: Frontiers Media SA
Date: 07-07-2016
Publisher: Elsevier BV
Date: 1989
DOI: 10.1016/0042-6989(89)90092-8
Abstract: The influence of uniform field flicker (UFF) on the contrast threshold for stationary sinusoidal gratings was measured as a function of flicker depth. Changing from no flicker to a flicker depth of 10% produces reliable differences in threshold. Further increases in flicker depth to 60% had little additional influence. The presence of UFF produces masking with low spatial frequency stimuli as expected but at higher spatial frequencies facilitation is obtained. The results are discussed in the context of the distinction between primate Magnocellular and Parvocellular pathways.
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 11-2010
DOI: 10.1167/IOVS.10-5290
Abstract: It has been proposed that reduced cortical inhibition might be a key feature of migraine. Here the authors compared migraine and control group performance for two visual motion tasks in which performance was considered to reflect center-surround inhibitory processes. These tasks use the observations that healthy young observers require longer stimulus durations to detect the direction of motion of larger higher contrast stimuli, and these stimuli also elicit weaker motion aftereffect (MAE) strength. Both observations are considered to arise from center-surround inhibition. The authors measured stimulus duration thresholds for detecting the direction of motion of stimuli of different sizes and contrasts, and also examined motion aftereffect strength for similar stimuli presented for longer durations in 20 control participants and 30 people with migraine (15 with aura). The migraine group was assessed between migraines while they were asymptomatic. For the motion direction task, a significant interaction existed between experimental group and contrast for large stimuli (F((3.96, 190.01)) = 2.95 P < 0.05) however, the interaction was in the opposite direction from that expected from reduced inhibition. Similarly, the MAE data demonstrated a significant interaction between stimulus size and group, but it was in the opposite direction from that predicted (F((1, 48)) = 4.13 P < 0.05). Consistent with previous studies, the migraine group in this study demonstrated abnormal visual motion processing. However, the data from both the motion direction detection and the motion aftereffect tasks do not support a theory of reduced cortical inhibition.
Publisher: Springer Science and Business Media LLC
Date: 17-06-2014
DOI: 10.3758/S13414-014-0710-7
Abstract: Although perception is typically constrained by limits in available processing resources, these constraints can be overcome if information about environmental properties, such as the spatial location or expected onset time of an object, can be used to direct resources to particular sensory inputs. In this work, we examined these temporal expectancy effects in greater detail in the context of the attentional blink (AB), in which identification of the second of two targets is impaired when the targets are separated by less than about half a second. We replicated previous results showing that presenting information about the expected onset time of the second target can overcome the AB. Uniquely, we also showed that information about expected onset (a) reduces susceptibility to distraction, (b) can be derived from salient temporal consistencies in intertarget intervals across exposures, and (c) is more effective when presented consistently rather than intermittently, along with trials that do not contain expectancy information. These results imply that temporal expectancy can benefit object processing at perceptual and postperceptual stages, and that participants are capable of flexibly encoding consistent timing information about environmental events in order to aid perception.
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 03-10-2012
DOI: 10.1167/12.11.3
Abstract: Adaptation in the visual system frequently results in properties of subsequently presented stimuli being repelled along identifiable axes. Adaptation to radial frequency (RF) patterns, patterns deformed from circular by a sinusoidal modulation of radius, results in a circle taking on the appearance of having modulation in opposite phase. Here we used paths of spatially localized gratings (Gabor patches) to examine the role of local orientation adaptation in this shape aftereffect. By applying the tilt aftereffect (TAE) as a function of the local orientation difference between adaptor and test, concomitant with adjustment of local position to accommodate the orientation change and preserve path continuity (Euler's method), we show that a TAE field can account for this misperception of shape. Spatial modulation is also observed spontaneously in a circular path of Gabor patches when the local patch orientations are rotated from tangential to the path. This illusory path modulation is consistent with the path orientation being attracted to the orientation of the patches. This consistent local rule implies a local explanation for the global effect and is consistent with a known illusion with a local cause, the Fraser illusion (FI). A similar analysis to that used for the TAE shows that the Fraser illusion can account for this particular alteration of perceived shape. A model which proposes that local orientations are encoded after considering the activation in a population of neurons with differing orientation tuning can accommodate both effects. It is proposed that these distinct processes rely on the same neural architecture.
Publisher: Oxford University Press (OUP)
Date: 24-07-2022
Abstract: The Western Australia Olfactory Memory Test (WAOMT) is a newly developed test designed to meet a need for a comprehensive measure of olfactory episodic memory (OEM) for clinical and research applications. This study aimed to establish the psychometric properties of the WAOMT in a s le of 209 community-dwelling older adults. An independent s le of 27 test-naïve participants were recruited to assess test retest reliability (between 7 and 28 days). Scale psychometric properties were examined using item response theory methods, combined s les (final N = 241). Convergent validity was assessed by comparing performance on the WAOMT with a comprehensive neuropsychological battery of domains (verbal and visual episodic memory, and odor identification), as well as other neuropsychological skills. Based on previous literature, it was predicted that the WAOMT would be positively correlated with conceptually similar cognitive domains. The WAOMT is a psychometrically sound test with adequate reliability properties and demonstrated convergent validity with tests of verbal and episodic memory and smell identification. Patterns of performance highlight learning and memory characteristics unique to OEM (e.g., learning curves, cued and free recall). Clinical and research implications include streamlining future versions of the WAOMT to ease patient and administrative burden, and the potential to reliably detect early neuropathological changes in healthy older adults with nonimpaired OEM abilities.
Publisher: Elsevier BV
Date: 10-1994
DOI: 10.1016/0042-6989(94)90246-1
Abstract: Second-order Type I and Type II plaids were constructed by combining two random-dot gratings. Each component consisted of a dynamic random-dot field, the contrast of which was modulated by a drifting sinusoidal grating. Orienting the two components suitably and interleaving at 120 Hz allowed us to produce a two-dimensional plaid pattern made from one-dimensional second-order components. The perceived direction of motion of both Type I and Type II plaids was measured as a function of stimulus duration. Type I plaids had a perceived direction close to the intersection of constraints/vector sum solution (which only coincide for these patterns) at all durations. Type II plaids had a perceived direction that moved away from the vector sum and toward the intersection of constraints solution as the duration of presentation increased. These results are similar in form to those found for plaids made from first-order (luminance-defined) components [Yo & Wilson (1992), Vision Research, 32, 135-147]. This suggests that a delay which operates specifically on second-order signals cannot be the sole cause for the change in perceived direction of Type II plaids made from first-order components [Wilson, Ferrera & Yo (1992), Visual Neuroscience, 9, 79-97].
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 18-09-2015
DOI: 10.1167/15.13.4
Abstract: The extended integration time of visual neurons can lead to the production of the neural equivalent of an orientation cue along the axis of motion in response to fast-moving objects. The dominant model argues that these motion streaks resolve the inherent directional uncertainty arising from the small size of receptive fields in V1, by combining spatial orientation with motion signals in V1. This model was tested in humans using visual aftereffects, in which adapting to a static grating causes the perceived direction of a subsequently presented motion stimulus to be tilted away from the adapting orientation. We found that a much broader range of orientations produced aftereffects than predicted by the current model, suggesting that these orientation cues influence motion perception at a later stage than V1. We also found that varying the spatial frequency of the adaptor changed the aftereffect from repulsive to attractive for motion-test but not form-test stimuli. Finally, manipulations of V1 excitability, using transcranial stimulation, reduced the aftereffect, suggesting that the orientation cue is dependent on V1. These results can be accounted for if the orientation information from the motion streak, gathered in V1, enters the motion system at a later stage of motion processing, most likely V5. A computational model of motion direction is presented incorporating gain modifications of broadly tuned motion-selective neurons by narrowly tuned orientation-selective cells in V1, which successfully accounts for the extant data. These results reinforce the suggestion that orientation places strong constraints on motion processing but in a previously undescribed manner.
Publisher: Wiley
Date: 06-1999
DOI: 10.1046/J.1440-1606.1999.00198.X
Abstract: Purpose: This experiment reports the independence of first‐ and second‐order processing mechanisms in form perception. Methods: Symmetrical dot patterns were created using either luminance‐increment dots (luminance above background), or texture‐defined dots (average luminance equal to background). The proportion of luminance increment or texture dots defining each pattern was varied among fields of noise dots of the same type to determine symmetry detection thresholds. Results: Differences in detection thresholds were found between luminance‐ and texture‐defined patterns. Further, symmetry detection thresholds for luminance‐increment dot patterns were resistant to noise defined by dots of opposite contrast polarity (luminance‐decrement dots) or texture, while texture‐defined patterns were resistant to neither texture nor luminance‐decrement noise. Conclusions: These data suggest that symmetry perception, along with other types of form perception, use both first‐ and second‐order processing mechanisms. The data are compatible with a second‐order system that includes a negative half‐wave rectifying non‐linearity.
Publisher: Elsevier BV
Date: 09-1995
DOI: 10.1016/0042-6989(95)00003-I
Abstract: The experiments reported here address the issue of whether the pathways which extract motion from first-order and second-order spatial patterns remain separate or whether they combine at some higher level in the motion system to form a single pathway. The question is addressed by investigating the interaction of first-order and second-order stimuli in the processing of a global-motion stimulus [a variant of the task introduced by Newsome & Pare (Journal of Neuroscience, 8, 2201-2211, (1988)]. Two experimental procedures were used. The first consisted of determining the effect of the addition of dots of one type (e.g. first order) undergoing purely random motion on the ability to extract the global-motion signal carried by dots of the other type (e.g. second order). The second experimental procedure consisted of determining the effect of maintaining a coherent-motion signal in one type of dot, moving in the opposite direction to the global-motion direction, on the ability to extract the global-motion signal carried by dots of the other type. The dots were matched for their effectiveness in producing a global motion percept and the results for both procedures were the same. First-order dots impaired the ability to extract second-order global-motion, and second-order dots had no effect on first-order global-motion extraction. It is argued that the sensitivity of the second-order global-motion system to the first-order dots is due to the ability of the second-order local-motion detectors to detect these dots. The present results are thus interpreted as indicating that the first-order and second-order motion pathways remain separate up to and including the level in the motion system at which global-motion signals are extracted.
Publisher: Elsevier BV
Date: 08-2022
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 24-09-2015
DOI: 10.1167/15.13.18
Abstract: The number of corners on the boundary of a closed contour is thought to be particularly critical for shape detection and discrimination. The aim of the current study was to examine the relative contribution of the number of corners and the angle between corners to shape discrimination in complex visual scenes as well as to determine the time course and neural substrates of global shape processing based on the presence or absence of these specific features. In Experiment 1, event-related potentials were recorded while participants discriminated between two radial frequency (RF) patterns with the same maximum local curvature defining corners but varying arrangements of those corners. The results showed that the angle separating corners was more critical than the overall number of corners for discrimination performance. An enhanced negativity (posterior N220) over the occipital lobe was elicited following the presentation of an RF with three modulation cycles (RF3) but not following a circle, suggesting that the posterior N220 is sensitive to variation in curvature on a contour. In Experiment 2, we confirm the primary effect of the presence of corners on the litude of the posterior N220 component and extend the stimuli to include shapes defined by texture. Source localization on the N170 and N220 components was conducted in Experiment 2, and a source in cortical area V4 was identified. These findings suggest that corners contain vital information for the discrimination of shapes. Additionally, this study shows that the perceptual characteristics and neuroanatomical substrates can be detected using electrophysiological measures.
Publisher: American Psychological Association (APA)
Date: 07-2019
DOI: 10.1037/XHP0000645
Abstract: Aftereffects of adaptation are frequently used to infer mechanisms of human visual perception. Commonly, the properties of stimuli are repelled from properties of the adaptor. For ex le, in the tilt aftereffect a line is repelled in orientation from a previously experienced line. Perceived orientation is predicted by the centroid of the responses of a population of mechanisms in idually tuned to limited ranges of orientation but collectively sensitive to the whole possible range. Aftereffects are also predictable if the mechanisms are allowed to adapt. Adaptation across radial frequency patterns, patterns deformed from circular by a sinusoidal modulation of radius, causes repulsive aftereffects, sensitive to the relative litudes and orientations of the patterns. Here we show that these shape aftereffects can be accounted for by the application of local tilt aftereffects around the shape contour. We suggest that fields of tilt aftereffects might provide a general mechanism for exaggerating the perceptual difference between successively experienced stimuli, making them more discriminable. If the human visual system does indeed exploit this possibility, then the conclusions often made by studies assuming adaptation within mechanisms sensitive to the shape of stimuli will need to be reconsidered. (PsycINFO Database Record (c) 2019 APA, all rights reserved).
Publisher: Elsevier BV
Date: 12-2019
DOI: 10.1016/J.VISRES.2019.10.003
Abstract: Perception of local properties of the visual field is influenced by aftereffects of adaptation. The tilt aftereffect describes repulsion of the perceived orientation of a line from the orientation of an adapting line. Analogous effects of spatial context are often called illusions. Repulsion of the perceived orientation of a grating from the orientation of a surrounding grating is referred to as the tilt illusion. In the same manner, the size aftereffect and Ebbinghaus illusion form a complementary pair of temporal and spatial context effects of size. Here we report psychophysical evidence for a previously unknown aspect-ratio illusion which causes the perceived aspect-ratio of a rectangle to be repelled from the aspect-ratio of rectangles surrounding it. This illusion provides a spatial analogue to the aspect-ratio aftereffect.
Publisher: Elsevier BV
Date: 09-1994
DOI: 10.1016/0042-6989(94)90288-7
Abstract: A spatial localization task was used to determine the accuracy of localization of random element clusters about their centroid. The random element clusters were generated within a circular region and the observers' task was to decide whether the cluster lay to the right or left of a reference line, defined by two vertically separated reference elements. Both the reference elements and the cluster elements themselves were comprised of spatially narrowband stimuli (gabor patches), and were presented at a constant suprathreshold level. The thresholds for localization of the element cluster were measured with varying element number, and for a number of different sizes of circular region and element. The relationship between localization threshold and element number was not monotonic. Thresholds were found to rise with increasing element number up to about six elements within a region, and to then fall with further increase in element number. Asymptotic thresholds at high element number were indistinguishable from those obtained for filled circles of the same size. The results do not conform to any one of a number of models based on a centroid analysis alone. By manipulating the spatial and orientational properties of the elements comprising the cluster to be localized it was determined that the more central mechanism underlying localization receive input from different spatial and orientation filters.
Publisher: Elsevier BV
Date: 1984
DOI: 10.1016/0042-6989(84)90017-8
Abstract: Discrimination of the relative spatial phase of sinusoids is reformulated as a local contrast discrimination task. This provides a good account of performance with gratings composed of a fundamental and either its second or fourth harmonic. The contrast of the compounds (including a fundamental and its third harmonic) are then varied, keeping the contrast ratio of the components constant, and it is found that performance improves with increasing contrast. The exponent of the power equation relating a base contrast measure to the contrast difference at threshold is derived (assuming the above reformulation to be valid). The average exponent (0.54) is in the range expected from contrast increment detection literature. The effect of contrast on performance is predicted very well. Phase per se does not need to be considered.
Publisher: Elsevier BV
Date: 12-2022
DOI: 10.1016/J.VISRES.2022.108139
Abstract: The perceived contrast of a central stimulus is supressed when it is embedded in a higher contrast surround, centre-surround suppression of contrast. Local brightness induction effects between the two stimulus regions have been proposed to account for conflicting results when relative grating phases were different. Here, suppression and brightness induction effects are dissociated using a centre-surround arrangement with moving gratings. Four experienced observers were involved in experiments, utilising two-interval forced-choice contrast matching tasks. The stimuli were drifting sinusoidal grating patterns with surrounds (95% contrast) differing in direction of motion and orientation relative to the 40% contrast centre grating. First a 90°-phase-offset same direction surround condition was compared to both same direction (phase aligned) and opposing direction conditions. The reduction in the suppression for the phase-offset condition suggested a reduction in brightness induction influences. Then suppression was examined when surround directions varied and where phase was either fixed or randomised. For small changes in the motion direction between centre and surround (0° to 26.6°) the amount of brightness induction varied sinusoidally with the difference in phase introduced by the direction difference. Finally, the spatial separation between the centre and surround was varied to determine the reduction of suppression and brightness induction with increasing spatial distance. We found both fit an exponential decay function, with surround suppression producing the larger range of influence. Our findings quantify both brightness induction and suppression effects and validate the use of phase randomisation to remove effects of brightness induction when evaluating surround suppression.
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 02-05-2018
DOI: 10.1167/18.5.4
Abstract: Within a natural scene it is not uncommon for an object's shape to be revealed over time. We investigated whether the same integration of shape information that happens around a fully visible contour also happens when that information is distributed over time. In a two-interval forced-choice task, observers discriminated between a radial frequency (RF) pattern and a circle that were revealed either using an implicit slit or traced out by a dot's motion and a line and a modulated line that were either contour-defined or motion-defined. First, with presentation times of approximately 1 s, we found no difference in the strength of integration when comparing a freely visible contour to one that (a) moved behind a slit (b) was revealed by a moving slit or (c) revealed piecemeal by a slit appearing at random locations (Experiment 1). Changing the duration of presentation (250-4,000 ms) had no effect on strength of integration or threshold for detection within the moving slit condition (Experiment 2). Considering these results, Experiment 3 revisited integration for a dot tracing out an RF path (Or, Thabet, Wilkinson, & Wilson, 2011), finding removal of a change in speed cue increased the strength of integration to that found in Experiments 1 and 2 of the current study. The pattern of results for modulated lines was different from RF patterns however, within these conditions, there was no difference in strength of integration between contour-defined and motion-defined stimuli. Our results suggest motion-defined patterns are processed as form from motion.
Publisher: Elsevier BV
Date: 2018
DOI: 10.1016/J.VISRES.2017.10.001
Abstract: Previous studies have found evidence for reduced cortical inhibition in aging visual cortex. Reduced inhibition could plausibly increase the spatial area of excitation in receptive fields of older observers, as weaker inhibitory processes would allow the excitatory receptive field to dominate and be psychophysically measureable over larger areas. Here, we investigated aging effects on spatial summation of motion direction using the Battenberg summation method, which aims to control the influence of locally generated internal noise changes by holding overall display size constant. This method produces more accurate estimates of summation area than conventional methods that simply increase overall stimulus dimensions. Battenberg stimuli have a checkerboard arrangement, where check size (luminance-modulated drifting gratings alternating with mean luminance areas), but not display size, is varied and compared with performance for a full field stimulus to provide a measure of summation. Motion direction discrimination thresholds, where contrast was the dependent variable, were measured in 14 younger (24-34 years) and 14 older (62-76 years) adults. Older observers were less sensitive for all check sizes, but the relative sensitivity across sizes, also differed between groups. In the older adults, the full field stimulus offered smaller performance improvements compared to that for younger adults, specifically for the small checked Battenberg stimuli. This suggests aging impacts on short-range summation mechanisms, potentially underpinned by larger summation areas for the perception of small moving stimuli.
Publisher: Brill
Date: 1985
Abstract: Sensitivity to a horizontal displacement of a vertical line was measured in order to ascertain the influence of the location of parallel flanking lines on the apparent position of features in visual space. The first experiment confirmed that the introduction of the flank added a component to the apparent shift which was towards the flank for small separations (less than 3-4') and away from the flank with larger separations. The second experiment investigated the notion that apparent location is derived by collecting information only from zones adjacent to the target and limited in the vertical extent by the target's height i.e. information orthogonal to the target's main axis. This was done by placing a vertical flank at a horizontal distance from the target that would be clearly within one zone or the other and measuring the effect of a vertical separation between the two flank halves. In the surround zone the amount of repulsion obtained was not influenced by vertical separation of the flank halves, even when they were several minutes higher (or lower) than the target line. In the central zone attraction was only obtained when the vertical separation was small enough to provide some overlap of the lines in the horizontal direction. With larger separations substantial repulsion was obtained. We conclude that while the central 'attraction' zone may only use information distributed in the direction of the line's displacement, it does so only within a 3-4' range on either side of the target line. The surround zone is not similarly limited in the region over which it collects information to influence the apparent location of features.
Publisher: Elsevier BV
Date: 02-2011
DOI: 10.1016/J.VISRES.2010.11.012
Abstract: Edwards and Badcock (Vision Research 35, 2589, 1995) argued for independent first-order (FO) and second-order (SO) motion systems up to and including the global-motion level. That study used luminance (which they called FO) and contrast (SO) modulated dots. They found that SO noise dots did not mask signal extraction with luminance increment dots while luminance increment dots did mask SO signal extraction. However, they argued this asymmetry was not due to a combined FO-SO pathway, but rather due to the fact that the luminance-modulated dots, being also local variations in contrast, are both FO and SO stimuli. We test their claim of FO and SO independence by using a stimulus that can generate pure FO and SO signals, specifically one consisting of multiple Gabors (the global-Gabor stimulus) in which the Gaussian envelopes are static and the carriers drift. The carrier can either be luminance-modulated (FO) or contrast-modulated (SO) and motion signals from the randomly-oriented local Gabors must be combined to detect the global-motion vector. Results show no cross-masking of FO and SO signals, thus supporting the hypothesis of independent FO and SO systems up to and including the level extracting optic-flow.
Publisher: Elsevier BV
Date: 04-2006
DOI: 10.1016/J.VISRES.2005.07.018
Abstract: Viewing a set of two thousand images in which the contrasts of a central and a surrounding pattern were highly correlated increased the suppressive influence of the surround on the perceived contrast of the central pattern. The apparent increase in inhibition supports the operation of an anti-Hebbian mechanism between the two groups of cells excited by the patterns (one group by the central pattern and the other by the surround). According to this mechanism, inhibitory connections between nearby cells increase in efficacy according to a simple function of the correlations between the cells' activities.
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 19-09-2014
DOI: 10.1167/14.11.12
Abstract: Recent research and modeling proposes that a closed shape is accurately described by both the curvature and angular location of its parts relative to the shape center, implying that the shape is coded along with its overall orientation. We tested this proposition. Radial frequency (RF) patterns were employed as stimuli as they can represent a range of familiar closed shapes and are processed globally. We measured a RF litude aftereffect (RFAAE) as a function of the shape orientation difference between adapt and test patterns of the same RF. For RF3 and RF4, RFAAEs were largest when adapt and test patterns were the same orientation, and then linearly decreased as the adaptor was rotated away from the test. RFAAEs did not, however, reach zero, instead plateauing significantly above zero. On the other hand, when adapt and test were of opposite luminance polarity, RFAAEs, although lower than same luminance-polarity RFAAEs, were invariant to differences between adapt and test orientations. Our findings provide evidence for two global shape mechanisms: one that is selective for shape orientation and luminance polarity, and one that is agnostic to these characteristics.
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 18-04-2008
DOI: 10.1167/8.4.12
Publisher: Elsevier BV
Date: 03-2008
DOI: 10.1016/J.SCHRES.2007.08.005
Abstract: Visuospatial working memory is not a unitary sketch pad but comprises independent dimensions of target distance and direction and at least two levels of detail (fine-grained and category level). The aim of this study was to examine these multiple aspects of encoding in patients with schizophrenia using a modified delayed response task. 42 patients with schizophrenia and 48 healthy controls pointed, as accurately as possible from a fixed starting position, to the visual location of target stimuli presented to a touch-sensitive screen. An adaptive staircase procedure was used to equate stimulus duration for each in idual. Encoding accuracy and maintenance of distance (mm) and direction ( degrees ) information was examined following a 0-second (immediate) or 4-second (unfilled) delay. Analyses utilized both absolute (unsigned) and signed data. The results showed that the average duration required to detect a target was significantly longer in patients than controls. When stimulus duration was equated, (a) the absolute accuracy of distance and direction responses was not significantly different between groups at 0-second delay but was significantly reduced at 4-second delay in patients with schizophrenia, and (b) signed direction errors at 4-second delay were significantly different between groups at stimulus angles greater than 90 degrees . The findings challenge previous suggestions of deficits in fine-grained encoding of spatial information in schizophrenia but confirm a difficulty maintaining both direction and distance details in working memory. Imprecision in spatial memory in schizophrenia also introduced greater bias from category level (prior) representations, especially in left hemi-space.
Publisher: Elsevier BV
Date: 1985
DOI: 10.1016/0042-6989(85)90011-2
Abstract: Adaptation to moving isoluminant gratings induces a motion after-effect (MAE). Isoluminant gratings are less effective at inducing and at nulling MAEs than are luminance gratings. These results are consistent with a low-level motion detection system which operates on signals from mechanisms which show both spatial and chromatic opponency.
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 02-2009
DOI: 10.1167/9.2.6
Publisher: SAGE Publications
Date: 09-2022
DOI: 10.1177/20416695221118111
Abstract: Induced motion is the illusory motion of a target away from the direction of motion of the unattended background. If it is a result of assigning background motion to self-motion and judging target motion relative to the scene as suggested by the flow parsing hypothesis then the effect must be mediated in higher levels of the visual motion pathway where self-motion is assessed. We provide evidence for a high-level mechanism in two broad ways. Firstly, we show that the effect is insensitive to a set of low-level spatial aspects of the scene, namely, the spatial arrangement, the spatial frequency content and the orientation content of the background relative to the target. Secondly, we show that the effect is the same whether the target and background are composed of the same kind of local elements—one-dimensional (1D) or two-dimensional (2D)—or one is composed of one, and the other composed of the other. The latter finding is significant because 1D and 2D local elements are integrated by two different mechanisms so the induced motion effect is likely to be mediated in a visual motion processing area that follows the two separate integration mechanisms. Area medial superior temporal in monkeys and the equivalent in humans is suggested as a viable site. We present a simple flow-parsing-inspired model and demonstrate a good fit to our data and to data from a previous induced motion study.
Publisher: Elsevier BV
Date: 1984
DOI: 10.1016/0042-6989(84)90116-0
Abstract: The ability of human observers to discriminate differences in the relative phase of the components of high contrast compound gratings has been investigated. It is found that difference of less than 10 degrees in the phase angle of the higher harmonic can be detected reliably, if sufficient practice is given. However, examination of the mechanisms involved in making "phase" discriminations suggests that observers, in most studies of phase discrimination, may not code relative phase directly in making their judgements. Indeed, it appears that the most parsimonious explanation is that the observers detect differences in the contrast of local regions of the stimuli.
Publisher: No publisher found
Date: 1996
DOI: 10.1016/0042-6989(95)00299-5
Abstract: It has been reported that equiluminant plaid patterns constructed from component gratings modulated along different axes of a cardinal colour space fail to create a coherent impression of two-dimensional motion [Krauskopf and Farell (1990). Nature, 348, 328-331]. In this paper we assess whether this lack of interaction between cardinal axes is a general finding or is instead dependent upon specific stimulus parameters. Type I and Type II plaids were made from sinusoidal components (1 cpd) each modulated along axes in a cardinal colour space and presented at equivalent perceived contrasts. The spatial angular difference between the two components was varied from 5 to 90 deg whilst keeping the Intersection of Constraints (I.O.C.) solution of the pattern constant. Observers were required to indicate the perceived direction of motion of the pattern in a single interval direction-identification task. We find that: (i) When plaids were made from components modulated along the same cardinal axis, coherent "pattern" motion was perceived at all angular differences. As the angular difference between the components decreased in a Type II plaid, the perceived direction of motion moved closer to the I.O.C. solution and away from that predicted by the vector sum. (ii) A plaid made from components modulated along red-green and blue-yellow cardinal axes (cross-cardinal axis) did not cohere at high angular differences (> 30 deg) but had a perceived direction of the fastest moving component. At lower angular differences, however, pattern motion was detected and approached the I.O.C. solution in much the same way as a same-cardinal axis Type II plaid. (iii) A plaid made from a luminance grating and a cardinal chromatic grating (red-green or blue-yellow) failed to cohere under all conditions, demonstrating that there is no interaction between luminance and chromatic cardinal axes. These results indicate that there are conditions under which red-green and blue-yellow cardinal components interact for the purposes of motion detection.
Publisher: Elsevier BV
Date: 11-1994
DOI: 10.1016/0042-6989(94)90054-X
Abstract: A number of experiments were conducted to investigate the interaction of the ON and OFF pathways in the processing of global-motion signals. The stimulus employed was a variant of that used by Newsome and Pare [(1988) Journal of Neuroscience, 8, 2201-2211] in which a small subset of dots move in a common (global-motion) direction in a field of randomly moving dots. The threshold measure was the number of dots required to move in the global-motion direction for that direction to be detected. We found that: (1) the extraction of a global-motion signal carried by light dots (luminance above the background) was impaired by the addition of dark dots (luminance below the background) which did not carry the signal (noise dots) (2) sub-threshold summation occurs for global-motion signals carried by light and dark dots and (3) a signal dot which changed luminance polarity (went from light to dark) did not result in a motion signal--either in the global-motion direction or in the opposite direction (reverse apparent motion). From these findings we conclude that the inputs to the motion sensitive cells have matched spatial opponency (the ON and OFF pathways remain separate at this level) but that they then combine to form a single pathway prior to the extraction of the global-motion signal. These findings are contrary to those predicted by models which advocate squaring or full-wave rectification prior to global motion processing.
Publisher: Frontiers Media SA
Date: 24-10-2018
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 04-2009
DOI: 10.1167/9.4.23
Publisher: Elsevier BV
Date: 07-2012
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 15-08-2011
DOI: 10.1167/11.9.5
Abstract: Visual saltation is the illusory mislocalization that occurs when multiple elements are rapidly presented to two peripheral locations mislocalized elements appear to fill in the intermediate space. We investigated the influence of element orientation on the path of illusory saltatory motion. Experiment 1 showed that congruence in element orientation at the two locations (horizontal-horizontal or vertical-vertical) produced rectilinear saltation, while incongruent orientations (vertical-horizontal or horizontal-vertical) elicited curvilinear saltation consistent with rigid rotation around a common point. In curvilinear saltation, mislocalized elements were perceived with an intermediate orientation. Experiment 2 showed that the perceived shape of the motion path was directly dependent on the salience of orientation information. In Experiment 3, we showed that the circular path of curvilinear saltation (induced by orientation incongruence) is altered by background motion (wedge-shaped regions of inward and outward moving dots) that overlaps only with the inter-element space. An ellipsoid path, where the major axis corresponds to the mislocalized element overlapping with outward motion and the minor axis corresponds to the mislocalized element overlapping with inward motion, is produced. These findings reveal that the interpretation of visual saltation arises from high-level computations in which the percept is derived through an interaction of form and motion.
Publisher: Elsevier BV
Date: 1982
Publisher: Elsevier BV
Date: 06-2023
Publisher: Elsevier BV
Date: 1985
DOI: 10.1016/0042-6989(85)90041-0
Abstract: Vernier acuity and jump detection were investigated using a perturbation technique, in which a flanking line is placed to one side of the target line. The size and direction of vernier displacement, or jump, required for no apparent change of location is strongly influenced by the separation between the flanking line and the test line and by its polarity. For flanks within a zone extending approximately 3'-4' to either side of the target line, the target's location is assigned to a weighted centroid of the complete luminance distribution: The target is pulled towards the flank, when the flank has a positive contrast polarity, and repelled when the polarity is negative. The effects of a dark flank on one side and a bright flank on the other are additive. Outside this central zone repulsion effects are obtained independent of the contrast polarity of the flank and flanks on opposite sides of the target line can cancel each other's influence. Varying the duration of the flank produces maximal effects in the surround with shorter duration than that required for maximal effects in the centre. Thus, while the localization contribution function resembles the popular difference of gaussians receptive field profile, it has two components reflecting differing mechanisms. In the centre the earlier centroid hypothesis can be applied with the addition of distance dependent weights. The surround has characteristics resembling the feature interaction seen in figural after-effects.
Publisher: SAGE Publications
Date: 05-2004
DOI: 10.1111/J.1468-2982.2004.00679.X
Abstract: This study was designed to determine whether cortical motion processing abnormalities are present in in iduals with migraine. Performance was measured using a visual motion coherence task (motion coherence perimetry, MCP) thought to depend on the operation of cortical area V5. Motion coherence thresholds were measured using stimuli composed of moving dots at 17 locations in the central ± 20° of visual field. Pre-cortical visual function was also measured using frequency doubling perimetry (FDP) at the same 17 locations. Several migraine subjects demonstrated significant pre-cortical visual functional abnormalities, however, most subjects had normal visual fields measured with FDP. Abnormal MCP performance was measured in 15 of 19 migraine-with-aura subjects, and 11 of 17 migraine-without-aura subjects. A decreased ability to detect coherent motion may possibly be explained by an increase in baseline neuronal noise, such as would be consistent with the concept of cortical hyperexcitability in migraine.
Publisher: Public Library of Science (PLoS)
Date: 31-05-2013
Publisher: Elsevier BV
Date: 05-2009
DOI: 10.1016/J.VISRES.2009.03.001
Abstract: Radial Frequency (RF) contours provide a unifying system to represent familiar shapes, such as triangles (RF3), squares (RF4) and pentagons (RF5), but it is not clear whether these sorts of shapes are detected by separate RF-tuned processes, or instead by a common shape mechanism. It has been suggested that multiple mechanisms are responsible for the detection of globally processed RF patterns, at least up to RF10. In this study, we used a sub-threshold summation paradigm to determine whether multiple shape channels are required to account for detection of RF patterns in this range. To do so, the modulation detection threshold required for discriminating an RF component in isolation from a circle, was compared to that obtained when a second, half-threshold litude, component was added to the single closed-contour. Threshold improvement occurred when the two shape components were the same RF, but usually not when the components differed in RF. These results cannot be explained by a single broadly-tuned shape channel and suggest that several narrow-band RF channels underpin detection of patterns below RF10, where the shapes have previously been shown to be processed globally.
Publisher: Springer Science and Business Media LLC
Date: 09-10-2013
DOI: 10.1007/S10803-012-1669-7
Abstract: Relative to low scorers, high scorers on the autism-spectrum quotient (AQ) show enhanced performance on the embedded figures test and the radial frequency search task (RFST), which has been attributed to both enhanced local processing and differences in combining global percepts. We investigate the role of local and global processing further using the RFST in four experiments. High AQ adults maintained a consistent advantage in search speed across erse target-distracter stimulus conditions. This advantage may reflect enhanced local processing of curvature in early stages of the form vision pathway and superior global detection of shape primitives. However, more probable is the presence of a superior search process that enables a consistent search advantage at both levels of processing.
Publisher: Elsevier BV
Date: 2010
DOI: 10.1016/J.NEUROPSYCHOLOGIA.2009.09.024
Abstract: The Embedded Figure Test (EFT) requires locating a simple shape embedded within a background of overlapping target-irrelevant scene elements. Observers with autism, or those with high levels of autistic-like traits, typically outperform matched comparison groups on the EFT. This research investigated the critical visual properties which give rise to this improved performance. The EFT is a search task and so here a radial frequency (RF) search task was created to directly explore efficacy of visual search and also the influence of element overlap on performance. In all conditions, the task was to detect whether the target RF3 (a triangular shape chosen for its visual properties) was present among a number of distracter RF4 (a square shape) patterns. The conditions employed were: 'singles', where all the patterns were spatially discrete, 'pairs', where two overlapping elements formed each cluster, and 'quads', comprising four overlapping elements per cluster. Compared to students scoring low on the Autism Spectrum Quotient (AQ n=27), those scoring high on the AQ (n=23) were faster on the EFT and also significantly less influenced by increasing set size of the stimulus array in all RF search task conditions. However, the group difference in RF search performance was unaffected by the amount of stimulus overlap. Thus a simple search task is sufficient to detect a performance advantage associated with higher levels of autistic traits and has the advantages of a solid footing in visual theory and being readily repeatable for the purpose of assessing performance variability and change with interventions.
Publisher: Elsevier BV
Date: 11-2009
DOI: 10.1016/J.VISRES.2009.08.026
Abstract: Cortical neurons that initially extract motion signals have small receptive-fields, and narrow orientation- and bandpass-spatial-frequency tuning. Accurate extraction of the veridical motion of objects typically requires the global pooling of the output of multiple local-motion units across orientation and space. We examined whether the narrow spatial-frequency tuning present at the local-motion level is preserved at the global-motion-pooling stage. Stimuli consisted of numerous drifting Gabor or plaid elements that were either signal (carrier drift-speed consistent with a given global-motion vector) or noise (drift speed consistent with a random, noise vector). The carrier spatial-frequencies of the signal and noise elements were independently varied. Regardless of the frequency of the signal elements, broad low-pass masking functions were obtained for both Gabor (one-dimensional) and Plaid (two-dimensional) conditions when measuring the threshold signal ratio for identification of the global-motion direction. For the Gabor stimuli, this pattern of results was also independent of the relative orientations of the signal and noise elements. These results indicate that in the global-motion pooling of one-dimensional and two-dimensional signals, local-motion signals of all spatial frequencies are pooled into a single system that exhibits broadband, low-pass tuning.
Publisher: MIT Press - Journals
Date: 02-2006
DOI: 10.1162/089976606775093891
Abstract: Slightly modified versions of an early Hebbian/anti-Hebbian neural network are shown to be capable of extracting the sparse, independent linear components of a prefiltered natural image set. An explanation for this capability in terms of a coupling between two hypothetical networks is presented. The simple networks presented here provide alternative, biologically plausible mechanisms for sparse, factorial coding in early primate vision.
Publisher: Elsevier BV
Date: 05-2010
DOI: 10.1016/J.BRAINRESBULL.2010.02.016
Abstract: The main aim of this review is to evaluate the proposal that several developmental disorders affecting vision share an impairment of the dorsal visual stream. First, the current definitions and common measurement approaches used to assess differences in both local and global functioning within the visual system are considered. Next, studies assessing local and global processing in the dorsal and ventral visual pathways are reviewed for five developmental conditions for which early to mid level visual abilities have been assessed: developmental dyslexia, autism spectrum disorders, developmental dyspraxia, Williams syndrome and Fragile X syndrome. The reviewed evidence is broadly consistent with the idea that the dorsal visual stream is affected in developmental disorders. However, the potential for a unique profile of visual abilities that distinguish some of the conditions is posited, given that for some of these disorders ventral stream deficits have also been found. We conclude with ideas regarding future directions for the study of visual perception in children with developmental disorders using psychophysical measures.
Publisher: Elsevier BV
Date: 08-1996
DOI: 10.1016/0042-6989(95)00321-5
Abstract: A number of experiments were conducted to investigate how global-motion performance varies with luminance contrast. When all the dots in the stimulus were the same contrast, performance improved with increasing contrast up to about the 15% level (Experiment 1). Increasing the contrast beyond this level had no additional effect on performance. When the contrast of a subgroup of the dots was varied, differential effects on performance could be obtained for contrasts up to the 80% level (Experiment 2). These results are interpreted as indicating that the performance saturation observed in Experiment 1 was due to the attainment of a performance ceiling at the global-motion level, and not due to contrast-response saturation of the underlying local-motion detectors. The results of earlier studies that have apparently found conflicting results (saturation vs no saturation) are discussed in light of the present results.
Publisher: American Association for the Advancement of Science (AAAS)
Date: 24-10-1980
Abstract: Contrast thresholds for sine-wave gratings of spatial frequencies of 2, 4, 12, and 16 cycles per degree were determined for normal and disabled readers at a range of stimulus durations. Normal readers demonstrated monotonically decreasing sensitivity with increasing spatial frequency at exposure durations between 40 and 100 milliseconds. At exposure durations of 150 to 1000 milliseconds, they showed peak sensitivity at 4 cycles per degree. In comparison, disabled readers showed monotonically decreasing sensitivity with increasing spatial frequency at all stimulus durations. The difference in sensitivity pattern across spatial frequencies was greatest at stimulus durations approximately equal to fixation durations during reading.
Publisher: Elsevier BV
Date: 03-2005
DOI: 10.1016/J.VISRES.2004.09.042
Abstract: The human visual system is adept at detecting global structure, or form, within a scene. The initial stage of post-retinal processing for all aspects of vision is fed by On- and Off-centre cells sensitive to centred luminance increments and decrements respectively. These cells provide input to two parallel pathways that process variations in local luminance (first-order pathway) and local contrast (second-order pathway). Here, we investigate the contribution of luminance and contrast information to global form detection, a stage between the extraction of local orientation and the recognition of objects. The underlying processes involve two stages. We find that signals in the On-, Off- and second-order pathways are segregated at both stages of processing. Surprisingly, the non-linear stage in the second-order form pathway is different from that in motion processing: the second-order form detectors show an asymmetry in sensitivity to increments and decrements that is not apparent in motion. A functional architecture for global form detection is proposed along with its possible neural substrates.
Publisher: Elsevier BV
Date: 1981
Publisher: MDPI AG
Date: 28-04-2022
DOI: 10.3390/SYM14050901
Abstract: EEG, fMRI and TMS studies have implicated the extra-striate cortex, including the Lateral Occipital Cortex (LOC), in the processing of visual mirror symmetries. Recent research has found that the sustained posterior negativity (SPN), a symmetry specific electrophysiological response identified in the region of the LOC, is generated when temporally displaced asymmetric components are integrated into a symmetric whole. We aim to expand on this finding using dynamic dot-patterns with systematically increased intra-pair temporal delay to map the limits of temporal integration of visual mirror symmetry. To achieve this, we used functional near-infrared spectroscopy (fNIRS) which measures the changes in the haemodynamic response to stimulation using near infrared light. We show that a symmetry specific haemodynamic response can be identified following temporal integration of otherwise meaningless dot-patterns, and the magnitude of this response scales with the duration of temporal delay. These results contribute to our understanding of when and where mirror symmetry is processed in the visual system. Furthermore, we highlight fNIRS as a promising but so far underutilised method of studying the haemodynamics of mid-level visual processes in the brain.
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 10-2005
DOI: 10.1167/IOVS.04-1406
Abstract: It is well known that glaucoma results in performance impairments on tasks processed early in the visual pathways. Glaucoma should also impair cortical visual processing because of reduced input from retinal ganglion cells and also possibly because of abnormal cortical function. This study was undertaken to assess whether cortically processed global percepts are disrupted in glaucoma in areas of visual field classified as normal by standard automated perimetry (SAP). Performance on global tasks (motion and form) was compared to measures of presumed precortical magnocellular and parvocellular function in the same in iduals. Fifteen control subjects and 12 patients with primary open-angle glaucoma participated. Testing was performed foveally and midperipherally (12.5 degrees). Contrast-discrimination thresholds were measured by using the steady-pedestal (magnocellular) and pulsed-pedestal (parvocellular) contrast-discrimination tasks of Pokorny and Smith. Global motion coherence and global form coherence thresholds were measured at high and low contrast. Patients with glaucoma demonstrated higher global motion and form-coherence thresholds than did control subjects for targets presented in the midperiphery (P < 0.05), but not foveally. Different in iduals performed poorly on the motion and form tasks. The subjects with the greatest presumed magnocellular and parvocellular loss were those with the largest deficits on the global motion and form tasks, respectively. Some subjects with glaucoma demonstrate profound impairments of global motion or global form integration in areas of visual field classified as normal by SAP. This finding implies that some people with glaucoma may have far greater difficulty with complex visual tasks (for ex le, navigation through the environment or face recognition) than is predicted by their visual field loss.
Publisher: Elsevier BV
Date: 1991
DOI: 10.1016/0042-6989(91)90115-L
Abstract: The eyes are in continuous motion. A robust system required to make spatial separation judgments should be resistant to the positional noise produced by such movements. Two parallel lines have been jittered horizontally in order to assess the impact of stimulus movement on the retina. Jitter that maintains the separation between the two lines has minimal effect on separation discrimination thresholds, regardless of whether the targets in the two eyes jitter in a positively correlated, negatively correlated or uncorrelated manner. Presenting both eyes with line pairs but only altering the separation in one eye in the second interval yields poorer performance. However, if one eye receives a change in separation while the other views a dark screen then that monocular threshold is very similar to the binocular threshold. These results are most simply explained by procedures which average the monocular separation estimates.
Publisher: American Psychological Association (APA)
Date: 06-1981
Publisher: Optica Publishing Group
Date: 07-1985
Abstract: We have used stimuli with difference-of-Gaussian (DOG) luminance profiles to measure depth-increment thresholds within postulated spatial channels as functions of depth from the fixation plane. Stereoacuity was best with high-frequency DOG's presented at the fixation plane. Performance was relatively constant for spatial frequency above 2.4 cycles/deg, but it deteriorated as spatial frequency was decreased. Regardless of spatial frequency, stereo sensitivity declined rapidly as stimuli were presented away from the horopter. The falloff occurred more rapidly over the 0-20-arc-min range than over the 20-80-arc-min range. Depth was perceived over a broader range of disparity pedestals with low-spatial-frequency stimuli however, the lowest thresholds were always obtained with the highest-frequency stimuli. Both the falloff of sensitivity with disparity pedestal and the disparity range of quantitative stereo depth lead to the conclusion that different size-tuned channels process disparity differently.
Publisher: International Society for the Scholarship of Teaching and Learning
Date: 22-09-2023
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 24-08-2017
DOI: 10.1167/17.9.18
Abstract: Previously, researchers have used circular contours with sinusoidal deformations of the radius (radial frequency [RF] patterns) to investigate the underlying processing involved in simple shape perception. On finding that the rapid improvement in sensitivity to deformation as more cycles of modulation were added was greater than expected from probability summation across sets of local independent detectors, they concluded that global integration of contour information was occurring. More recently, this conclusion has been questioned by researchers using a method of calculating probability summation derived from signal detection theory (Baldwin, Schmidtmann, Kingdom, & Hess, 2016). They could not distinguish between global integration and probability summation. Furthermore, it has been argued that RF patterns and lines are processed in a similar manner (Mullen, Beaudot, & Ivanov, 2011 Schmidtmann & Kingdom, 2017). The current study investigates these claims using fixed-phase (in which the local elements have spatial certainty) and random-phase (in which the local elements have spatial uncertainty) RF patterns and modulated lines. Thresholds were collected from eight naïve observers and compared to probability summation estimates calculated using methods derived from both high threshold theory and signal detection theory. The results indicate global processing of random-phase RF patterns and evidence for an interaction between local and global cues for fixed-phase RF patterns. They also show no evidence of global integration with modulated line stimuli. The results provide further evidence for the global processing of random-phase RF patterns and indicate that RF patterns and modulated lines are processed differently.
Publisher: Springer Science and Business Media LLC
Date: 19-03-2021
DOI: 10.3758/S13423-020-01874-W
Abstract: The visual system uses parallel pathways to process information. However, an ongoing debate centers on the extent to which the pathways from the retina, via the Lateral Geniculate nucleus to the visual cortex, process distinct aspects of the visual scene and, if they do, can stimuli in the laboratory be used to selectively drive them. These questions are important for a number of reasons, including that some pathologies are thought to be associated with impaired functioning of one of these pathways and certain cognitive functions have been preferentially linked to specific pathways. Here we examine the two main pathways that have been the focus of this debate: the magnocellular and parvocellular pathways. Specifically, we review the results of electrophysiological and lesion studies that have investigated their properties and conclude that while there is substantial overlap in the type of information that they process, it is possible to identify aspects of visual information that are predominantly processed by either the magnocellular or parvocellular pathway. We then discuss the types of visual stimuli that can be used to preferentially drive these pathways.
Publisher: Frontiers Media SA
Date: 23-02-2016
Location: United Kingdom of Great Britain and Northern Ireland
Start Date: 2016
End Date: 03-2019
Amount: $291,882.00
Funder: Australian Research Council
View Funded ActivityStart Date: 2019
End Date: 07-2022
Amount: $419,137.00
Funder: Australian Research Council
View Funded ActivityStart Date: 2006
End Date: 12-2009
Amount: $235,000.00
Funder: Australian Research Council
View Funded ActivityStart Date: 2019
End Date: 12-2022
Amount: $390,724.00
Funder: Australian Research Council
View Funded ActivityStart Date: 09-2003
End Date: 05-2006
Amount: $194,000.00
Funder: Australian Research Council
View Funded ActivityStart Date: 12-2003
End Date: 12-2004
Amount: $10,000.00
Funder: Australian Research Council
View Funded ActivityStart Date: 2013
End Date: 12-2015
Amount: $294,000.00
Funder: Australian Research Council
View Funded ActivityStart Date: 07-2011
End Date: 06-2016
Amount: $582,074.00
Funder: Australian Research Council
View Funded ActivityStart Date: 2010
End Date: 12-2013
Amount: $338,408.00
Funder: Australian Research Council
View Funded Activity