ORCID Profile
0000-0003-2729-1808
Current Organisation
University of California, Berkeley
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Publisher: Elsevier BV
Date: 05-2010
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 09-03-2007
DOI: 10.1167/7.2.10
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 02-1999
DOI: 10.1097/00006324-199902000-00019
Abstract: We assessed the influence of dioptric and diffusive blur on normal subjects' letter and Vernier acuity in two experiments. In the first experiment, letter acuity was measured for isolated black Sloan letters and Vernier acuity was determined for a pair of black vertical abutting or nonabutting lines. Targets were viewed through plus lenses that produced 0, 1, 2, 4, and 8 D of dioptric blur. In the second experiment, letter acuity was determined for bright 4-position Ts and Vernier acuity was measured for a pair of bright abutting vertical lines. Six levels of imposed diffusive blur were produced by varying the distance between a ground glass screen and the oscilloscope on which the targets were presented. The results of both experiments indicate that letter and Vernier acuity for abutting or closely separated lines worsen in parallel curvilinear fashion, as long as the lines comprising the Vernier targets remain equally detectable when various amounts of dioptric and diffusive blur are imposed. We conclude that both dioptric and diffusive blur introduce common processing limitations for letter and Vernier acuity.
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 05-04-2019
DOI: 10.1167/19.4.10
Abstract: Recent research has suggested that the visual span in stimulus identification can be enlarged through perceptual learning. Since both English and music reading involve left-to-right sequential symbol processing, music-reading experience may enhance symbol identification through perceptual learning particularly in the right visual field (RVF). In contrast, as Chinese can be read in all directions, and components of Chinese characters do not consistently form a left-right structure, this hypothesized RVF enhancement effect may be limited in Chinese character identification. To test these hypotheses, here we recruited musicians and nonmusicians who read Chinese as their first language (L1) and English as their second language (L2) to identify music notes, English letters, Chinese characters, and novel symbols (Tibetan letters) presented at different eccentricities and visual field locations on the screen while maintaining central fixation. We found that in English letter identification, significantly more musicians achieved above-chance performance in the center-RVF locations than nonmusicians. This effect was not observed in Chinese character or novel symbol identification. We also found that in music note identification, musicians outperformed nonmusicians in accuracy in the center-RVF condition, consistent with the RVF enhancement effect in the visual span observed in English-letter identification. These results suggest that the modulation of music-reading experience on the visual span for stimulus identification depends on the similarities in the perceptual processes involved.
Publisher: Elsevier BV
Date: 07-2007
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 12-2000
Publisher: Informa UK Limited
Date: 09-1989
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 02-2011
Publisher: Elsevier BV
Date: 2007
Publisher: Optica Publishing Group
Date: 06-2000
Abstract: Previously we showed that thresholds for abutting Vernier targets are unaffected by motion, as long as the targets are processed by the same spatial-frequency channel at each velocity and remain equally detectable [Invest. Ophthalmol. Visual Sci. (Suppl.) 37, S734 (1996)]. In this study we compared Vernier thresholds for stationary and moving abutting and nonabutting targets (gaps = 0, 18, and 36 arc min) for velocities of 0-16 deg/s. The Vernier targets were spatially filtered vertical lines (peak spatial frequency = 3.3 or 6.6 c/deg), presented at contrast levels of two, four, and eight times the detection threshold of each component line. Unlike the results for abutting targets, Vernier thresholds for nonabutting targets worsen with velocity as well as gap size. The results for abutting Vernier targets are consistent with the hypothesis that thresholds are mediated by oriented spatial filters, whose responses increase proportionally with the stimulus contrast. The velocity-dependent thresholds found for nonabutting Vernier targets can be explained on the basis of local-sign comparisons if the comparison process is assumed to include a small amount of temporal noise.
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 05-2016
Publisher: Wiley
Date: 11-01-2020
DOI: 10.1111/OPO.12664
Abstract: Reading is vital to full participation in modern society. To millions of people suffering from macular disease that results in a central scotoma, reading is difficult and inefficient, rendering reading as the primary goal for most patients seeking low vision rehabilitation. The goals of this review paper are to summarize the dependence of reading speed on several key visual and typographical factors and the current methods or technologies for improving reading performance for people with macular disease. In general, reading speed for people with macular disease depends on print size, text contrast, size of the visual span, temporal processing of letters and oculomotor control. Attempts at improving reading speed by reducing the crowding effect between letters, words or lines or optimizing properties of typeface such as the presence of serifs or stroke‐width thickness proved to be futile, with any improvement being modest at best. Currently, the most promising method to improve reading speed for people with macular disease is training, including perceptual learning or oculomotor training. The limitation on reading speed for people with macular disease is likely to be multi‐factorial. Future studies should try to understand how different factors interact to limit reading speed, and whether different methods could be combined to produce a much greater benefit.
Publisher: Elsevier BV
Date: 09-2018
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 09-2018
DOI: 10.1097/OPX.0000000000001229
Abstract: Little is known about how the preferred retinal locus (PRL) develops in patients with macular disease. We found that acuity is worse at the PRL than at other retinal locations around the scotoma, suggesting that the selection of the PRL location is unlikely to be based on optimizing acuity. Following the onset of bilateral macular disease, most patients adopt a retinal location outside the central scotoma, the PRL, as their new retinal location for visual tasks. Very little information is known about how the location of a PRL is chosen. In this study, we tested the hypothesis that the selection of the location for a PRL is based on optimizing visual acuity, which predicts that acuity is the best at the PRL, compared with other retinal locations. Using a scanning laser ophthalmoscope that allowed us to position visual targets at precise retinal locations, we measured acuity psychophysically using a four-orientation Tumbling-E presented at the PRL and at multiple (ranged between 23 and 36 across observers) locations around the scotoma for five observers with bilateral macular disease. For all five observers, the acuity at the PRL was never the best among all testing locations. Instead, acuities were better at 15 to 86% of the testing locations other than the PRL, with the best acuity being 17 to 58% better than that at the PRL. The locations with better acuities did not cluster around the PRL and did not necessarily lie at the same distance from the fovea or the PRL. Our finding that acuity is worse at the PRL than at other locations around the scotoma implies that the selection of the PRL location is unlikely to be based on optimizing acuity.
Publisher: Elsevier BV
Date: 10-2003
DOI: 10.1016/S0042-6989(03)00436-X
Abstract: Recent psychophysical studies have been interpreted to indicate that the perception of motion temporally either lags or is synchronous with the perception of color. These results appear to be at odds with neurophysiological data, which show that the average response-onset latency is shorter in the cortical areas responsible for motion (e.g., MT and MST) than for color processing (e.g., V4). The purpose of this study was to compare the perceptual asynchrony between motion and color on two psychophysical tasks. In the color correspondence task, observers indicated the predominant color of an 18 degrees x 18 degrees field of colored dots when they moved in a specific direction. On each trial, the dots periodically changed color from red to green and moved cyclically at 15, 30 or 60 deg/s in two directions separated by 180 degrees, 135 degrees, 90 degrees or 45 degrees. In the temporal order judgment task, observers indicated whether a change in color occurred before or after a change in motion, within a single cycle of the moving-dot stimulus. In the color correspondence task, we found that the perceptual asynchrony between color and motion depends on the difference in directions within the motion cycle, but does not depend on the dot velocity. In the temporal order judgment task, the perceptual asynchrony is substantially shorter than for the color correspondence task, and does not depend on the change in motion direction or the dot velocity. These findings suggest that it is inappropriate to interpret previous psychophysical results as evidence that motion perception generally lags color perception. We discuss our data in the context of a "two-stage sustained-transient" functional model for the processing of various perceptual attributes.
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 02-2019
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 15-03-2002
DOI: 10.1167/2.7.696
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 05-2010
DOI: 10.1167/10.5.16
Publisher: Elsevier BV
Date: 03-2003
DOI: 10.1016/S0042-6989(02)00628-4
Abstract: The ability to see fine detail diminishes when the target of interest moves at a speed greater than a few deg/s. The purpose of this study was to identify fundamental limitations on spatial acuity that result from image motion. Discrimination of Vernier offset was measured for a pair of vertical abutting lines and letter resolution was measured using a four-orientation letter 'T'. These stimuli were digitally filtered using one of five band-pass (bandwidth=1.5 octaves) filters with a center frequency between 0.83 and 13.2 c/deg, and presented at velocities that ranged from 0 to 12 deg/s. Filtered and unfiltered stimuli were presented for 150 ms at a constant multiple (4x or 2x) of the contrast-detection threshold at each velocity. For stimuli of low to middle spatial frequency (up to 3.3 c/deg), Vernier and letter acuity for equally detectable targets are essentially unaffected by velocity up to 12 deg/s, i.e., for temporal frequencies of motion (velocity x spatial frequency) up to approximately 50 Hz. For stimuli of higher spatial frequency, acuity remains essentially constant until the velocity corresponds to a temporal frequency of about 30 Hz, and increases thereafter. Both Vernier and letter acuities worsen by approximately a factor of two for each one-octave decrease in filter spatial frequency. Both types of acuities worsen also as the contrast of the stimulus is reduced, but Vernier discrimination exhibits a stronger contrast-dependence than letter resolution. Our results support previous suggestions that a shift in the spatial scale used by the visual system to analyze spatial stimuli is principally responsible for the degradation of acuity in the presence of image motion. The results are consistent with a spatio-temporal-frequency limitation on spatial thresholds for moving stimuli, and not with a temporal-frequency limitation per se.
Publisher: Elsevier BV
Date: 03-2006
Publisher: Cold Spring Harbor Laboratory
Date: 16-11-2017
DOI: 10.1101/220319
Abstract: Human eyes are never stable, even during attempts of maintaining gaze on a visual target. Considering transient response characteristics of retinal ganglion cells, a certain amount of motion of the eyes is required to efficiently encode information and to prevent neural adaptation. However, excessive motion of the eyes leads to insufficient exposure to the stimuli which creates blur and reduces visual acuity. Normal miniature eye movements fall in between these extremes but it is unclear if they are optimally tuned for seeing fine spatial details. We used a state-of-the-art retinal imaging technique with eye tracking to address this question. We sought to determine the optimal gain (stimulus/eye motion ratio) that corresponds to maximum performance in an orientation discrimination task performed at the fovea. We found that miniature eye movements are tuned, but may not be optimal, for seeing fine spatial details.
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 02-2007
DOI: 10.1167/7.2.2
Publisher: Elsevier BV
Date: 03-2001
DOI: 10.1016/S0042-6989(00)00295-9
Abstract: Our goal is to link spatial and temporal properties of letter recognition to reading speed for text viewed centrally or in peripheral vision. We propose that the size of the visual span - the number of letters recognizable in a glance - imposes a fundamental limit on reading speed, and that shrinkage of the visual span in peripheral vision accounts for slower peripheral reading. In Experiment 1, we estimated the size of the visual span in the lower visual field by measuring RSVP (rapid serial visual presentation) reading times as a function of word length. The size of the visual span decreased from at least 10 letters in central vision to 1.7 letters at 15 degrees eccentricity, in good agreement with the corresponding reduction of reading speed measured by Chung and coworkers (Chung, S. T. L., Mansfield, J. S., & Legge, G. E. (1998). Psychophysics of reading. XVIII. The effect of print size on reading speed in normal peripheral vision. Vision Research, 38, 2949-2962). In Exp. 2, we measured letter recognition for trigrams (random strings of three letters) as a function of their position on horizontal lines passing through fixation (central vision) or displaced downward into the lower visual field (5, 10 and 20 degrees ). We also varied trigram presentation time. We used these data to construct visual-span profiles of letter accuracy versus letter position. These profiles were used as input to a parameter-free model whose output was RSVP reading speed. A version of this model containing a simple lexical-matching rule accounted for RSVP reading speed in central vision. Failure of this version of the model in peripheral vision indicated that people rely more on lexical inference to support peripheral reading. We conclude that spatiotemporal characteristics of the visual span limit RSVP reading speed in central vision, and that shrinkage of the visual span results in slower reading in peripheral vision.
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 07-03-2007
DOI: 10.1167/7.2.9
Publisher: Elsevier BV
Date: 06-1998
DOI: 10.1016/S0042-6989(97)00327-1
Abstract: Vernier and letter acuities are both susceptible to degradation by image motion. In a previous study, we showed that the worsening of Vernier acuity for stimuli moving up to 4 degrees/s is accounted for primarily by a shift of visual sensitivity to mechanisms of lower spatial frequency. The purposes of this study were to extend the previous results for Vernier acuity to higher stimulus contrast and velocities, and to determine if a shift in spatial scale can similarly explain the degradation of letter acuity for moving stimuli. We measured Vernier discrimination for a pair of vertical abutting thin lines and letter resolution for a four-orientation letter 'T' as a function of stimulus velocity ranging from 0 to 12 degrees/s. Stimuli were presented at 20 times the detection threshold, determined for each velocity. To determine the spatial-frequency mechanism that mediates each task at each velocity, we measured Vernier and letter acuities with low-pass filtered stimuli (cut-off spatial-frequency: 17.1-1.67 c/deg) and analyzed the data using an equivalent blur analysis. Our results show that the empirically determined, equivalent intrinsic blur associated with both tasks increases as a function of stimulus velocity, suggesting corresponding increases in the size of optimally responding mechanisms. This progressive increase in mechanism size can account for the worsening of Vernier and letter acuities with velocity. Vernier discrimination is found to be more susceptible to degradation by various stimulus parameters than letter resolution, suggesting that different mechanisms are involved in the two tasks. We conclude that the elevations in Vernier and letter acuities for moving stimuli are the consequence of a shift of visual sensitivity toward mechanisms of lower spatial frequencies.
Publisher: Elsevier BV
Date: 09-1997
DOI: 10.1016/S0042-6989(97)00057-6
Abstract: The purpose of this study was to examine the hypothesis that higher stimulus velocities could be tolerated in amblyopic and normal peripheral vision. The basis for this hypothesis is that a shift in the spatial scale of processing appears to account for the degradation in vernier acuity for moving stimuli in normal vision, and, to a large degree for the degradation in vernier acuity for stationary stimuli in amblyopic and peripheral vision. Vernier thresholds were determined using a pair of long abutting lines, for velocities ranging between 0 and 8 deg/sec. Comparisons were made between non-amblyopic and amblyopic eyes in two amblyopic observers, and between central and peripheral (5 and 10 deg) vision in two normal observers. We analyzed our threshold vs velocity data using an equivalent noise analysis, and defined the knee of the function, the point at which vernier threshold is elevated by a factor of square root of 2, as the "critical velocity" beyond which image motion degrades vernier acuity. Critical velocities were found to be higher in amblyopic than in nonamblyopic eyes and higher in peripheral than central vision. Our results are consistent with the predictions from the shift in spatial scale notion--that higher velocity of image motion can be tolerated because of the shift in sensitivity toward lower spatial-frequency filter mechanisms in amblyopic and normal peripheral vision.
Publisher: Elsevier BV
Date: 03-2008
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 27-02-2020
DOI: 10.1167/JOV.20.2.12
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 07-2013
Publisher: Public Library of Science (PLoS)
Date: 30-04-2012
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 05-1997
Publisher: Elsevier BV
Date: 06-2001
DOI: 10.1016/S0042-6989(01)00071-2
Abstract: Crowding, the difficulty in recognizing a letter flanked by other letters, has been explained as a lateral masking effect. The purpose of this study was to examine the spatial-frequency and contrast dependencies of crowding, and to compare them with the properties of pattern masking. In experiment 1, we measured contrast thresholds for identifying the middle letters in strings of three randomly chosen lower-case letters (trigrams), for a range of letter spacings. Letters were digitally filtered using a set of bandpass filters, with peak object spatial frequencies ranging from 0.63 to 10 c/letter. Bandwidth of the filters was 1 octave. Frequencies of the target and flanking letters were the same, or differed by up to 2 octaves. Contrast of the flanking letters was fixed at the maximum value. Testing was conducted at the fovea and 5 degrees eccentricity. We found that crowding exhibits spatial-tuning functions like masking, but with generally broader bandwidths than those for masking. The spatial extent of crowding was found to be about 0.5 deg at the fovea and 2 deg at 5 degrees eccentricity, independent of target letter frequency. In experiment 2, we measured the contrast thresholds for identifying the middle target letters in trigrams for a range of flanking letter contrasts at 5 degrees eccentricity. At low flanker contrast, crowding does not show a facilitatory region, unlike pattern masking. At high flanker contrast, threshold rises with contrast with an exponent of 0.13-0.3, lower than corresponding exponents for pattern masking. In experiment 3, we varied the contrast ratio between the flanking letters and the target letters, and found that the magnitude of crowding increases monotonically with contrast ratio. This finding contradicts a prediction based on a grouping explanation for crowding. Our results are consistent with the postulation that crowding and masking may share the same first stage linear filtering process, and perhaps a similar second-stage process, with the additional property that the second-stage process in crowding pools information over a spatial extent that varies with eccentricity.
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 03-2015
Publisher: Elsevier BV
Date: 12-2002
DOI: 10.1016/S0960-9822(02)01354-4
Abstract: After an observer adapts to a moving stimulus, texture within a stationary stimulus is perceived to drift in the opposite direction-the traditional motion aftereffect (MAE). It has recently been shown that the perceived position of objects can be markedly influenced by motion adaptation. In the present study, we examine the selectivity of positional shifts resulting from motion adaptation to stimulus attributes such as velocity, relative contrast, and relative spatial frequency. In addition, we ask whether spatial position can be modified in the absence of perceived motion. Results show that when adapting and test stimuli have collinear carrier gratings, the global position of the object shows a substantial shift in the direction of the illusory motion. When the carrier gratings of the adapting and test stimuli are orthogonal (a configuration in which no MAE is experienced), a global positional shift of similar magnitude is found. The illusory positional shift was found to be immune to changes in spatial frequency and to contrast between adapting and test stimuli-manipulations that dramatically reduce the magnitude of the traditional MAE. The lack of sensitivity for stimulus characteristics other than direction of motion suggests that a specialized population of cortical neurones, which are insensitive to changes in a number of rudimentary visual attributes, may modulate positional representation in lower cortical areas.
Publisher: Elsevier BV
Date: 05-2022
DOI: 10.1016/J.VISRES.2022.108012
Abstract: Crowding refers to the deleterious visual interaction among nearby objects. Does maximal crowding occur when objects are closest to one another in space and time? We examined how crowding depends on the spatial and temporal proximity, retinally and perceptually, between a target and flankers. Our target was a briefly flashed T-stimulus presented at 10° right of fixation (3-o'clock position). It appeared at different target-onset-to-flanker asynchronies with respect to the instant when a pair of flanking Ts, revolving around the fixation target, reached the 3-o'clock position. Observers judged the orientation of the target-T (the crowding task), or its position relative to the revolving flankers (the flash-lag task). Performance was also measured in the absence of flanker motion: target and flankers were either presented simultaneously (closest retinal temporal proximity) with different angular spatial offsets, or were presented collinearly (closest retinal spatial proximity) with different temporal onset asynchronies. We found that neither retinal nor perceptual spatial or temporal proximity could account for when maximal crowding occurred. Simulations using a model based on feed-forward interactions between sustained and transient channels in static and motion pathways, taking into account the differential response latencies, can explain the crowding functions observed under various spatio-temporal conditions between the target and flankers.
Publisher: Wiley
Date: 02-2010
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 25-03-2019
Publisher: Elsevier BV
Date: 11-2007
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 18-04-2016
DOI: 10.1167/16.6.8
Publisher: ACM
Date: 22-10-2023
Publisher: Elsevier BV
Date: 06-2001
Publisher: Elsevier BV
Date: 11-1995
DOI: 10.1016/0042-6989(95)00090-M
Abstract: This study determined how contour interaction (the degradation of visual acuity by the presence of nearby contours) is affected by the incessant retinal image motion that occurs in observers with congenital nystagmus (CN). Visual acuity was measured for single, high-contrast, black Landolt Cs, presented without and with flanking bars (contour-to-C separation = 1, 2, 5, or 10 multiples of the gap width of the C). Stimuli were presented against either a white or a black surround. For comparison, acuity was also determined in normal observers, with and without motion of the stimulus to simulate the retinal image motion in jerk CN. The results show that the peak magnitude of contour interaction (the maximal degradation in acuity attributable to contour interaction) is significantly larger in the observers with CN than in normals. When acuity targets are presented against a black surround, contour interaction also occurs over a wider spatial extent in the observers with CN. Imposed image motion increases the extent of contour interaction in normal observers, but not sufficiently to account fully for the results of the observers with CN. We suggest that the additional contour interaction found in observers with CN may be attributable to the presence of amblyopia. For a small contour-to-C separation, contour interaction is significantly greater when stimuli are presented against a black rather than a white surround. Consequently, single-letter acuity may be appreciably underestimated clinically when an adjustable window is used to isolate letters on a projected acuity chart.
Publisher: Elsevier BV
Date: 05-2013
Publisher: Society for Neuroscience
Date: 13-11-2013
DOI: 10.1523/JNEUROSCI.2764-13.2013
Abstract: Single-unit recordings demonstrated that the adult mammalian visual cortex is capable of reorganizing after induced retinal lesions. In humans, whether the adult cortex is capable of reorganizing has only been studied using functional magnetic resonance imaging, with equivocal results. Here, we exploited the phenomenon of visual crowding, a major limitation on object recognition, to show that, in humans with long-standing retinal (macular) lesions that afflict the fovea and thus use their peripheral vision exclusively, the signature properties of crowding are distinctly different from those of the normal periphery. Crowding refers to the inability to recognize objects when the object spacing is smaller than the critical spacing. Critical spacing depends only on the retinal location of the object, scales linearly with its distance from the fovea, and is approximately two times larger in the radial than the tangential direction with respect to the fovea, thus demonstrating the signature radial–tangential anisotropy of the crowding zone. Using retinal imaging combined with behavioral measurements, we mapped out the crowding zone at the precise peripheral retinal locations adopted by in iduals with macular lesions as the new visual reference loci. At these loci, the critical spacings are substantially smaller along the radial direction than expected based on the normal periphery, resulting in a lower scaling of critical spacing with the eccentricity of the peripheral locus and a loss in the signature radial–tangential anisotropy of the crowding zone. These results imply a fundamental difference in the substrate of cortical processing in object recognition following long-term adaptation to macular lesions.
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 06-2011
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 11-1999
DOI: 10.1097/00006324-199911000-00024
Abstract: This study compared the effectiveness of a head-mounted video magnifier, low-vision enhancement system (LVES), with closed-circuit TV (CCTV) and large print as a device or means of improving reading performance in people with low vision. The reading performance of ten low-vision participants was assessed in two ways: (1) By measuring reading speed as a function of print size with LVES and without LVES, and (2) by comparing reading speed and comprehension of news articles using the LVES vs. a popular non-head-mounted video magnifier, the CCTV. Maximum reading speeds with LVES matched the maximum reading speeds with unaided vision attained by enlarging print. The critical print size (the smallest print size that could be read at maximum reading speed) improved significantly for all participants using LVES compared with unaided vision. When comparing reading performance using LVES and CCTV, we found that reading speed and comprehension for the two conditions were equivalent. The two low-vision participants with lowest acuities (20/640 and 20/960) could not read the 10-point newspaper articles with LVES, even with an 8 D auxiliary reading lens that permitted a very close reading distance. Head-mounted video magnifiers, such as LVES, can support good low-vision reading performance, but the restricted range of magnification may limit the usefulness of the device as a reading magnifier for people with very low acuity.
Publisher: Elsevier BV
Date: 10-2006
Publisher: Elsevier BV
Date: 06-2002
DOI: 10.1016/S0042-6989(02)00065-2
Abstract: Amblyopia is characterized by a deficit in identifying small letters (acuity deficit) in the absence of identifiable ocular pathology. One explanation for this deficit is that the amblyopic visual system lacks appropriate channels tuned to high spatial frequencies for identifying small letters. The purpose of this study was to examine the spatial-frequency properties of letter identification in the amblyopic visual system. To do so, we measured contrast thresholds for identifying letters that were band-pass filtered to different bands of spatial frequencies, for letter sizes ranging from 2x to 19.2x larger than acuity letters. Letters were digitally filtered using a set of band-pass filters, with peak object spatial frequencies ranging from 0.88 to 10 c/letter. The bandwidth of the filters was 1 octave. For any given letter size, contrast sensitivity for identifying letters exhibits a spatial-tuning function. The shape of these tuning functions was found to be similar between amblyopic and non-amblyopic eyes, and across all letter sizes. The peak of these functions shifted progressively toward lower object spatial frequency when the letter size became smaller. When compared with the non-amblyopic eyes, the amblyopic eyes have a limited range of tuning functions sensitive to letters. However, when scaled with respect to acuity, the relationship between the peak frequency of the tuning functions and letter size becomes essentially identical in the amblyopic and non-amblyopic eyes. An ideal-observer analysis that takes into account spectral information about letter identity and the contrast-sensitivity function of the observer, but does not invoke narrow-band channels, also shows that the properties of the tuning functions for letter identification are similar between the amblyopic and non-amblyopic eyes. We conclude that the deficit in identifying small letters in amblyopes is not attributable to differences in the shape or selection of "channels", when compared with the normal visual system. Rather, it is a consequence of the difference in the resolution limit between the amblyopic and the non-amblyopic eyes.
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 09-2012
Publisher: The Royal Society
Date: 02-2017
DOI: 10.1098/RSOS.160559
Abstract: Objects that are briefly flashed around the time of saccades are mislocalized. Previously, robust interactions between saccadic perceptual distortions and stimulus contrast have been reported. It is also known that crowding depends on the contrast of the target and flankers. Here, we investigated how stimulus contrast and crowding interact with pre-saccadic perception. We asked observers to report the orientation of a tilted Gabor presented in the periphery, with or without four flanking vertically oriented Gabors. Observers performed the task either following a saccade or while maintaining fixation. Contrasts of the target and flankers were independently set to either high or low, with equal probability. In both the fixation and saccade conditions, the flanked conditions resulted in worse discrimination performance—the crowding effect. In the unflanked saccade trials, performance significantly decreased with target-to-saccade onset for low-contrast targets but not for high-contrast targets. In the presence of flankers, impending saccades reduced performance only for low-contrast, but not for high-contrast flankers. Interestingly, average performance in the fixation and saccade conditions was mostly similar in all contrast conditions. Moreover, the magnitude of crowding was influenced by saccades only when the target had high contrast and the flankers had low contrasts. Overall, our results are consistent with modulation of perisaccadic spatial localization by contrast and saccadic suppression, but at odds with a recent report of pre-saccadic release of crowding.
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 06-2013
Publisher: Elsevier BV
Date: 05-2005
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 04-2010
Publisher: Frontiers Media SA
Date: 23-12-2014
Publisher: Elsevier BV
Date: 2010
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 12-06-2017
DOI: 10.1167/17.5.18
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 29-10-2004
DOI: 10.1167/4.10.6
Publisher: Springer Science and Business Media LLC
Date: 2013
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 09-12-2016
DOI: 10.1167/16.15.10
Publisher: Elsevier BV
Date: 09-2015
Publisher: Elsevier BV
Date: 11-2018
Publisher: Annual Reviews
Date: 14-10-2016
DOI: 10.1146/ANNUREV-VISION-111815-114344
Abstract: Low vision is any type of visual impairment that affects activities of daily living. In the context of low vision, we define plasticity as changes in brain or perceptual behavior that follow the onset of visual impairment and that are not directly due to the underlying pathology. An important goal of low-vision research is to determine how plasticity affects visual performance of everyday activities. In this review, we consider the levels of the visual system at which plasticity occurs, the impact of age and visual experience on plasticity, and whether plastic changes are spontaneous or require explicit training. We also discuss how plasticity may affect low-vision rehabilitation. Developments in retinal imaging, noninvasive brain imaging, and eye tracking have supplemented traditional clinical and psychophysical methods for assessing how the visual system adapts to visual impairment. Findings from contemporary research are providing tools to guide people with low vision in adopting appropriate rehabilitation strategies.
Publisher: Optica Publishing Group
Date: 11-1996
Abstract: The purpose of this study was to determine whether Ricco's diameter, the spatial extent within which sensitivity demonstrates a perfect reciprocity between contrast and area, enlarges as the stimulus velocity increases. Detection thresholds were measured for a single line of length 10 arcmin as a function of linewidth that varied between 0.31 and 21.7 arcmin and for velocity ranging from 0 to 6 deg/s. We fitted the detection threshold versus linewidth data with two power functions of slope 0 and 1 and defined the intersection of these two functions as Ricco's diameter. For an increase in velocity from 0 to 6 deg/s, Ricco's diameter increases in dimension by approximately a factor of 4. Similar results were obtained when Ricco's diameter was estimated by comparing detection threshold of a thin line to that of an edge. The increase in Ricco's diameter with stimulus velocity suggests that the spatial-frequency mechanism that mediates line detection shifts progressively toward lower spatial frequencies for faster moving stimuli.
Publisher: Brill
Date: 07-07-2012
Publisher: Elsevier BV
Date: 02-2007
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 28-09-2012
DOI: 10.1167/IOVS.12-9821
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 25-10-2021
DOI: 10.1167/JOV.21.11.18
Publisher: Elsevier BV
Date: 08-2002
DOI: 10.1016/S0042-6989(02)00092-5
Abstract: Spatial-frequency characteristics of letter identification are much better understood in the fovea than in the periphery. The purpose of this study was to compare the spatial-frequency characteristics of letter identification in central and peripheral vision. We measured contrast thresholds for identifying single, Times-Roman lower-case letters that were spatially band-pass filtered. Each of the 26 letters was digitally filtered with a set of nine cosine log filters, with peak object spatial frequencies ranging from 0.63 to 10 c/letter, in half-octave steps. Bandwidth of the filters was 1 octave. Three observers with normal vision were each tested monocularly at the fovea, and at 5 degrees and 10 degrees in the inferior visual field. Letter sizes were 0.2, 0.4 and 0.6 log units larger than high contrast, unfiltered acuity letters. Plots of contrast sensitivity for letter identification vs. frequency of the band-pass filters exhibit spatial tuning. In general, the spatial-frequency characteristics of letter identification are fundamentally identical between central and peripheral vision. These characteristics include the scaling of the peak frequency of the spatial-tuning functions with letter size and the bandwidth of the tuning functions. The only difference between the fovea and the periphery is that for the same physical letter size, peak sensitivity of the spatial-tuning functions occurs at a higher retinal frequency at the fovea than in the periphery. To test whether or not the contrast sensitivity function (CSF) can account for the differences in the spatial-frequency characteristics of letter identification between central and peripheral vision, we incorporated a human CSF into an ideal-observer model, and tested the performance of this ideal-observer on the same letter identification task used with the human observers. Data from this CSF-ideal-observer resemble closely those of human observers, suggesting that the spatial-frequency characteristics of human letter identification can be accounted for by the CSF and the letter-identity information, without invoking selection among narrow-band spatial-frequency channels.
Publisher: Elsevier BV
Date: 08-2019
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 05-07-2011
DOI: 10.1167/11.8.1
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 07-2004
DOI: 10.1097/00006324-200407000-00014
Abstract: Crowding, the adverse spatial interaction due to proximity of adjacent targets, has been suggested as an explanation for slow reading in peripheral vision. The purposes of this study were to (1) demonstrate that crowding exists at the word level and (2) examine whether or not reading speed in central and peripheral vision can be enhanced with increased vertical word spacing. Five normal observers read aloud sequences of six unrelated four-letter words presented on a computer monitor, one word at a time, using rapid serial visual presentation (RSVP). Reading speeds were calculated based on the RSVP exposure durations yielding 80% correct. Testing was conducted at the fovea and at 5 degrees and 10 degrees in the inferior visual field. Critical print size (CPS) for each observer and at each eccentricity was first determined by measuring reading speeds for four print sizes using unflanked words. We then presented words at 0.8x or 1.4x CPS, with each target word flanked by two other words, one above and one below the target word. Reading speeds were determined for vertical word spacings (baseline-to-baseline separation between two vertically separated words) ranging from 0.8x to 2x the standard single-spacing, as well as the unflanked condition. At the fovea, reading speed increased with vertical word spacing up to about 1.2x to 1.5x the standard spacing and remained constant and similar to the unflanked reading speed at larger vertical word spacings. In the periphery, reading speed also increased with vertical word spacing, but it remained below the unflanked reading speed for all spacings tested. At 2x the standard spacing, peripheral reading speed was still about 25% lower than the unflanked reading speed for both eccentricities and print sizes. Results from a control experiment showed that the greater reliance of peripheral reading speed on vertical word spacing was also found in the right visual field. Increased vertical word spacing, which presumably decreases the adverse effect of crowding between adjacent lines of text, benefits reading speed. This benefit is greater in peripheral than central vision.
Publisher: Springer Science and Business Media LLC
Date: 12-1995
DOI: 10.1007/BF00230050
Abstract: Methicillin-resistant
Publisher: Elsevier BV
Date: 04-2004
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 08-2014
Publisher: Elsevier BV
Date: 06-2007
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 14-03-2002
DOI: 10.1167/2.7.35
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 09-2012
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 14-03-2010
DOI: 10.1167/2.7.31
Publisher: Elsevier BV
Date: 08-1996
DOI: 10.1016/0042-6989(95)00342-8
Abstract: Vernier acuity is susceptible to degradation by image motion. The purpose of this study was to determine to what extent vernier thresholds are elevated in the presence of image motion because of reduced stimulus visibility, due to contrast smearing, or to a shift in the spatial scale of analysis. To test the visibility hypothesis, we measured vernier thresholds as a function of stimulus velocity (0-6 deg/sec), for various levels of stimulus visibility, each normalized to the detection threshold at the respective velocity. Contrary to the prediction of the visibility hypothesis, vernier thresholds worsen as the velocity increases, even when the stimuli are equally visible. To test the shift in spatial scale hypothesis, we determined spatial frequency tuning functions for vernier discrimination and line detection tasks, using a masking paradigm. We measured vernier and line detection thresholds as a function of spatial frequency of a sine-wave mask (0.5-32 c/deg), and for stimulus and mask velocities ranging from 0 to 4 deg/sec. Peak masking for both vernier discrimination and line detection, which indicates the most sensitive band of spatial frequencies for each task, shifts systematically toward lower spatial frequencies as the velocity increases. The progressive increase in spatial scale largely accounts for the worsening of vernier thresholds for moving stimuli. Differences between peak masking for vernier discrimination and line detection were found at 0 and 1 deg/sec, suggesting that different mechanisms mediate the two tasks, at least at low velocities. The masking results are consistent with previous findings that directionally selective motion detectors mediate detection of moving stimuli, but suggest that these detectors do not analyze vernier offsets. We conclude that the elevation of vernier threshold for a moving stimulus is accounted for primarily by a shift of sensitivity to mechanisms of lower spatial frequency, and not by decreased stimulus visibility.
Publisher: Elsevier BV
Date: 08-2014
Publisher: Elsevier BV
Date: 10-2016
Publisher: Elsevier BV
Date: 09-2015
Publisher: Frontiers Media SA
Date: 07-08-2017
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 2014
DOI: 10.1167/14.6.3
Publisher: Elsevier BV
Date: 08-2012
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 21-01-2016
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 28-01-2021
DOI: 10.1167/JOV.21.1.14
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 10-05-2018
DOI: 10.1167/18.5.8
Publisher: Elsevier BV
Date: 02-2010
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 14-03-2010
DOI: 10.1167/1.3.411
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 27-01-2017
DOI: 10.1167/17.1.33
Publisher: Cambridge University Press (CUP)
Date: 29-08-2012
DOI: 10.1017/S0140525X12000325
Abstract: Reading speed matters in most real-world contexts, and it is a robust and easy aspect of reading to measure. Theories of reading should account for speed.
Publisher: Elsevier BV
Date: 04-2010
Publisher: Elsevier BV
Date: 11-2009
Publisher: Oxford University Press (OUP)
Date: 05-07-2014
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 09-2008
Publisher: Elsevier BV
Date: 03-2019
Publisher: Elsevier BV
Date: 12-2018
Publisher: Psychology Press
Date: 10-08-2007
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 07-2020
DOI: 10.1167/IOVS.61.8.2
Publisher: Elsevier BV
Date: 2013
Publisher: Informa UK Limited
Date: 11-1990
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 29-04-2020
DOI: 10.1167/JOV.20.4.24
Publisher: Elsevier BV
Date: 2012
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 15-03-2010
DOI: 10.1167/2.7.279
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 18-08-2014
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 18-03-2010
DOI: 10.1167/3.9.815
Publisher: Elsevier BV
Date: 05-2016
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 02-1996
DOI: 10.1097/00006324-199602000-00004
Abstract: Foveation periods are brief intervals in the congenital nystagmus (CN) waveform when the image is on or near the fovea and eye velocity is relatively slow. The purpose of this study was to determine how visual acuity depends on image velocity for foveation periods of different durations. Visual acuity was measured using high-contrast, single Landolt Cs in four normal observers during image motion simulating that in jerk nystagmus. The "simulated foveation periods" ranged from 20 to 100 ms in duration and 0 to 16 degrees approximately in velocity. The "critical velocity" was defined as the velocity during simulated foveation periods that produced a just-noticeable worsening of acuity (0.05 and 0.1 logMAR) from that in the zero-velocity condition. Critical velocity increased from approximately 3 degrees approximately for simulated foveation durations between 100 and 40 ms to approximately 5 degrees approximately for a simulated foveation duration of 20 ms. Critical velocities increased further when the targets were presented peripherally or with optical blur, to introduce an additional acuity loss. A consequence of these findings is that less recovery of acuity should be expected when retinal image motion is reduced in in iduals with CN if a sensory acuity deficit coexists.
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 18-03-2003
DOI: 10.1167/3.9.811
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 08-2009
DOI: 10.1167/9.9.16
Publisher: Elsevier BV
Date: 10-1998
DOI: 10.1016/S0042-6989(98)00072-8
Abstract: Reading in peripheral vision is slow and requires large print, posing substantial difficulty for patients with central scotomata. The purpose of this study was to evaluate the effect of print size on reading speed at different eccentricities in normal peripheral vision. We hypothesized that reading speeds should remain invariant with eccentricity, as long as the print is appropriately scaled in size--the scaling hypothesis. The scaling hypothesis predicts that log-log plots of reading speed versus print size exhibit the same shape at all eccentricities, but shift along the print-size axis. Six normal observers read aloud single sentences (approximately 11 words in length) presented on a computer monitor, one word at a time, using rapid serial visual presentation (RSVP). We measured reading speeds (based on RSVP exposure durations yielding 80% correct) for eight print sizes at each of six retinal eccentricities, from 0 (foveal) to 20 deg in the inferior visual field. Consistent with the scaling hypothesis, plots of reading speed versus print size had the same shape at different eccentricities: reading speed increased with print size, up to a critical print size and was then constant at a maximum reading speed for larger print sizes. Also consistent with the scaling hypothesis, the plots shifted horizontally such that average values of the critical print size increased from 0.16 deg (fovea) to 2.22 deg (20 deg peripheral). Inconsistent with the scaling hypothesis, the plots also exhibited vertical shifts so that average values of the maximum reading speed decreased from 807 w.p.m. (fovea) to 135 w.p.m. (20 deg peripheral). Because the maximum reading speed is not invariant with eccentricity even when the print size was scaled, we reject the scaling hypothesis and conclude that print size is not the only factor limiting maximum reading speed in normal peripheral vision.
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 28-02-2011
DOI: 10.1167/IOVS.10-6034
Publisher: Elsevier BV
Date: 07-2009
Publisher: Elsevier BV
Date: 09-2013
Publisher: Elsevier BV
Date: 03-2004
DOI: 10.1016/J.VISRES.2003.09.028
Abstract: Visual-span profiles are plots of letter-recognition accuracy as a function of letter position left or right of the midline. Previously, we have shown that contraction of these profiles in peripheral vision can account for slow reading speed in peripheral vision. In this study, we asked two questions: (1) can we modify visual-span profiles through training on letter-recognition, and if so, (2) are these changes accompanied by changes in reading speed? Eighteen normally sighted observers were randomly assigned to one of three groups: training at 10 degrees in the upper visual field, training at 10 degrees in the lower visual field and a no-training control group. We compared observers' characteristics of reading (maximum reading speed and critical print size) and visual-span profiles (peak litude and bits of information transmitted) before and after training, and at trained and untrained retinal locations (10 degrees upper and lower visual fields). Reading speeds were measured for six print sizes at each retinal location, using the rapid serial visual presentation paradigm. Visual-span profiles were measured using a trigram letter-recognition task, for a letter size equivalent to 1.4x the critical print size for reading. Training consisted of the repeated measurement of 20 visual-span profiles (over four consecutive days) in either the upper or lower visual field. We also tracked the changes in performance in a sub-group of observers for up to three months following training. We found that the visual-span profiles can be expanded (bits of information transmitted increased by 6 bits) through training with a letter-recognition task, and that there is an accompanying increase (41%) in the maximum reading speed. These improvements transferred, to a large extent, from the trained to an untrained retinal location, and were retained, to a large extent, for at least three months following training. Our results are consistent with the view that the visual span is a bottleneck on reading speed, but a bottleneck that can be increased with practice.
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 1999
DOI: 10.1097/00006324-199901000-00029
Abstract: The purpose of this study was to investigate the size of the pupil while viewing through yellow and neutral density (ND) filters. Previous studies have shown that the pupil of the human eye is relatively more sensitive to short wavelengths than indicated by the photopic luminosity curve. We first measured the consensual horizontal pupil diameter of 11 observers as a function of luminance (0.144 to 18,150 cd/m2) to establish the luminance-response function for each observer. We then measured the pupil diameter while the observer viewed through a Corning Photochromic Filter (CPF) 550 lens and two ND filters (ND 0.5 and 1.0). The pupil diameters obtained with each filter were compared to the diameters at an equivalent luminance based upon each observer's luminance-response function. Our results show that the pupil diameter is larger with the yellow lens than when viewing a broad spectrum white field at an equivalent luminance. We speculate that our results may explain some, but not all, of the well-known subjective brightness enhancement that occurs when viewing through yellow filters.
Location: United States of America
Start Date: 2005
End Date: 2010
Funder: National Institutes of Health
View Funded ActivityStart Date: 2000
End Date: 2005
Funder: National Institutes of Health
View Funded ActivityStart Date: 2016
End Date: 2016
Funder: Aix-Marseille Université
View Funded Activity