ORCID Profile
0000-0001-5711-6408
Current Organisation
University of Melbourne
Does something not look right? The information on this page has been harvested from data sources that may not be up to date. We continue to work with information providers to improve coverage and quality. To report an issue, use the Feedback Form.
Publisher: Elsevier BV
Date: 04-2016
Publisher: American Psychological Association (APA)
Date: 02-2019
DOI: 10.1037/EDU0000287
Publisher: EDP Sciences
Date: 06-2020
DOI: 10.1051/0004-6361/202037923
Abstract: Context. The HR 1614 is an overdensity in velocity space and has for a long time been known as an old (∼2 Gyr) and metal-rich ([Fe/H] ≈ +0.2) nearby moving group that has a dissolving open cluster origin. The existence of such old and metal-rich groups in the solar vicinity is quite unexpected since the vast majority of nearby moving groups are known to be young. Aims. In the light of new and significantly larger data sets than ever before (astrometric, photometric, and spectroscopic), we aim to re-investigate the properties and origin of the HR 1614 moving group. If the HR 1614 overdensity is a dissolving cluster, its stars should represent a single-age and single-elemental abundance population. Methods. To identify and characterise the HR 1614 moving group we use astrometric data from Gaia DR2 distances, extinction, and reddening corrections from the StarHorse code elemental abundances from the GALAH and APOGEE spectroscopic surveys and photometric metallicities from the SkyMapper survey. Bayesian ages were estimated for the SkyMapper stars. Since the Hercules stream is the closest kinematical structure to the HR 1614 moving group in velocity space and as its origin is believed to be well-understood, we use the Hercules stream for comparison purposes. Stars that are likely to be members of the two groups were selected based on their space velocities. Results. The HR 1614 moving group is located mainly at negative U velocities, does not form an arch of constant energy in the U − V space, and is tilted in V . We find that the HR 1614 overdensity is not chemically homogeneous, but that its stars exist at a wide range of metallicities, ages, and elemental abundance ratios. They are essentially similar to what is observed in the Galactic thin and thick discs, a younger population (around 3 Gyr) that is metal-rich (−0.2 ≤ [Fe/H] ≤ 0.4) and alpha-poor. These findings are very similar to what is seen for the Hercules stream, which is believed to have a dynamical origin and consists of regular stars from the Galactic discs. Conclusions. The HR 1614 overdensity has a wide spread in metallicity, [Mg/Fe], and age distributions resembling the general properties of the Galactic disc. It should therefore not be considered a dissolving open cluster, or an accreted population. Based on the kinematic and chemical properties of the HR 1614 overdensity we suggest that it has a complex origin that could be explained by combining several different mechanisms such as resonances with the Galactic bar and spiral structure, phase mixing of dissolving spiral structure, and phase mixing due to an external perturbation.
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 20-10-2020
Publisher: Elsevier BV
Date: 2019
DOI: 10.2139/SSRN.3438365
Publisher: Springer Science and Business Media LLC
Date: 08-07-2022
DOI: 10.1038/S41467-022-31675-9
Abstract: Quantifying the timing (duration and frequency) of brief visual events is vital to human perception, multisensory integration and action planning. Tuned neural responses to visual event timing have been found in association cortices, in areas implicated in these processes. Here we ask how these timing-tuned responses are related to the responses of early visual cortex, which monotonically increase with event duration and frequency. Using 7-Tesla functional magnetic resonance imaging and neural model-based analyses, we find a gradual transition from monotonically increasing to timing-tuned neural responses beginning in the medial temporal area (MT/V5). Therefore, across successive stages of visual processing, timing-tuned response components gradually become dominant over inherent sensory response modulation by event timing. This additional timing-tuned response component is independent of retinotopic location. We propose that this hierarchical emergence of timing-tuned responses from sensory processing areas quantifies sensory event timing while abstracting temporal representations from spatial properties of their inputs.
Publisher: Elsevier BV
Date: 05-2020
Publisher: Cold Spring Harbor Laboratory
Date: 29-03-2021
DOI: 10.1101/2021.03.28.437364
Abstract: Human early visual cortex response litudes monotonically increase with numerosity (object number), regardless of object size and spacing. However, numerosity is typically considered a high-level visual or cognitive feature, while early visual responses follow image contrast in the spatial frequency domain. We found that, at fixed contrast, aggregate Fourier power (at all orientations and spatial frequencies) followed numerosity closely but nonlinearly with little effect of object size, spacing or shape. This would allow straightforward numerosity estimation from spatial frequency domain image representations. Using 7T fMRI, we showed monotonic responses originate in primary visual cortex (V1) at the stimulus’s retinotopic location. Responses here and in neural network models followed aggregate Fourier power more closely than numerosity. Truly numerosity tuned responses emerged after lateral occipital cortex and were independent of retinotopic location. We propose numerosity’s straightforward perception and neural responses may have built on behaviorally beneficial spatial frequency analyses in simpler animals.
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 08-2023
Publisher: Research Square Platform LLC
Date: 14-02-2023
DOI: 10.21203/RS.3.RS-2560452/V1
Abstract: Visual short-term memory (VSTM), intentionally remembering image features, relies on interacting sensory and executive processes. Sensory processing relies on tuned responses, organized in hierarchical networks of topographic maps. How does the brain distribute responses to task demands across neural populations? We examined neural responses to the number of remembered visual items (VSTM load) using ultra-high field fMRI (7T). We describe neural populations showing tuned responses to VSTM load in an extensive series of topographic maps, hierarchically increasing in VSTM load preferences from posterior sensory to anterior executive areas. These responses are absent when viewing the same stimuli without varying task demands, and appear unrelated to response preferences for visual position and numerosity. These results generalize principles of neural tuning, topographic organization, and hierarchical transformations from sensory encoding to distribution of task demands across neural populations.
Publisher: SAGE Publications
Date: 22-06-2018
Abstract: In numerate societies, early arithmetic development is associated with visuospatial working memory, executive functions, nonverbal intelligence, and magnitude-comparison abilities. To what extent do these associations arise from cultural practices or general cognitive prerequisites? Here, we administered tests of these cognitive abilities (Corsi Blocks, Raven’s Colored Progressive Matrices, Porteus Maze) to indigenous children in remote northern Australia, whose culture contains few counting words or counting practices, and to nonindigenous children from an Australian city. The indigenous children completed a standard nonverbal addition task the nonindigenous children completed a comparable single-digit addition task. The correlation matrices among variables in the indigenous and nonindigenous children showed similar patterns of relationships, and parallel regression analyses showed that visuospatial working memory was the main predictor of addition performance in both groups. Our findings support the hypothesis that the same cognitive capacities promote competence for learners in both numerate and nonnumerate societies.
Publisher: Frontiers Media SA
Date: 14-08-2018
Publisher: Springer Science and Business Media LLC
Date: 15-03-2022
DOI: 10.1038/S41467-022-29030-Z
Abstract: Human early visual cortex response litudes monotonically increase with numerosity (object number), regardless of object size and spacing. However, numerosity is typically considered a high-level visual or cognitive feature, while early visual responses follow image contrast in the spatial frequency domain. We find that, at fixed contrast, aggregate Fourier power (at all orientations and spatial frequencies) follows numerosity closely but nonlinearly with little effect of object size, spacing or shape. This would allow straightforward numerosity estimation from spatial frequency domain image representations. Using 7T fMRI, we show monotonic responses originate in primary visual cortex (V1) at the stimulus’s retinotopic location. Responses here and in neural network models follow aggregate Fourier power more closely than numerosity. Truly numerosity tuned responses emerge after lateral occipital cortex and are independent of retinotopic location. We propose numerosity’s straightforward perception and neural responses may result from the pervasive spatial frequency analyses of early visual processing.
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 29-03-2017
DOI: 10.1167/17.3.16
Abstract: We habitually move our eyes when we enumerate sets of objects. It remains unclear whether saccades are directed for numerosity processing as distinct from object-oriented visual processing (e.g., object saliency, scanning heuristics). Here we investigated the extent to which enumeration eye movements are contingent upon the location of objects in an array, and whether fixation patterns vary with enumeration demands. Twenty adults enumerated random dot arrays twice: first to report the set cardinality and second to judge the perceived number of subsets. We manipulated the spatial location of dots by presenting arrays at 0°, 90°, 180°, and 270° orientations. Participants required a similar time to enumerate the set or the perceived number of subsets in the same array. Fixation patterns were systematically shifted in the direction of array rotation, and distributed across similar locations when the same array was shown on multiple occasions. We modeled fixation patterns and dot saliency using a simple filtering model and show participants judged groups of dots in close proximity (2°-2.5° visual angle) as distinct subsets. Modeling results are consistent with the suggestion that enumeration involves visual grouping mechanisms based on object saliency, and specific enumeration demands affect spatial distribution of fixations. Our findings highlight the importance of set computation, rather than object processing per se, for models of numerosity processing.
Publisher: Elsevier BV
Date: 08-2022
DOI: 10.1016/J.NEUBIOREV.2022.104753
Abstract: Subitizing is the fast and accurate enumeration of small sets. Whether attention is necessary for subitizing remains controversial considering (1) subitizing is claimed to be "pre-attentive", and (2) existing experimental methods and results are inconsistent. To determine whether manipulations to attention demonstratively affect subitizing, the current study comprises a systematic review and meta-analysis. Results from fourteen studies (22 experiments, 35 comparisons) suggest that changes to attentional demands interferes with enumeration of small sets leading to slower response times, lower accuracy, and poorer Weber acuity (p < .010 p < .001 p < .001 respectively)-notwithstanding a potential publication bias. A unifying framework is proposed to explain the role of attention in visual enumeration, with progressively greater attentional involvement from estimation to subitizing to counting. Our findings suggest attention is integral for subitizing and highlights the need to emphasise attentional mechanisms into neurocognitive models of numerosity processing. We also discuss the possible role of attention in numerical processing difficulties (e.g., dyscalculia).
Publisher: Elsevier BV
Date: 04-2020
Publisher: Frontiers Media SA
Date: 15-05-2015
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 05-12-2022
Publisher: Elsevier BV
Date: 09-2022
DOI: 10.1016/J.NEUROIMAGE.2022.119366
Abstract: Perception of sub-second auditory event timing supports multisensory integration, and speech and music perception and production. Neural populations tuned for the timing (duration and rate) of visual events were recently described in several human extrastriate visual areas. Here we ask whether the brain also contains neural populations tuned for auditory event timing, and whether these are shared with visual timing. Using 7T fMRI, we measured responses to white noise bursts of changing duration and rate. We analyzed these responses using neural response models describing different parametric relationships between event timing and neural response litude. This revealed auditory timing-tuned responses in the primary auditory cortex, and auditory association areas of the belt, parabelt and premotor cortex. While these areas also showed tonotopic tuning for auditory pitch, pitch and timing preferences were not consistently correlated. Auditory timing-tuned response functions differed between these areas, though without clear hierarchical integration of responses. The similarity of auditory and visual timing tuned responses, together with the lack of overlap between the areas showing these responses for each modality, suggests modality-specific responses to event timing are computed similarly but from different sensory inputs, and then transformed differently to suit the needs of each modality.
Publisher: Informa UK Limited
Date: 02-06-2015
DOI: 10.1080/09297049.2015.1038989
Abstract: The stepping-stone variant of the hidden pathway maze learning (HPML) task paradigm has been extensively used to investigate cognitive functions in neuropsychology and neuropharmacology. Previous studies have used total error across trials, as well as rule-break errors and learning errors, to define spatial memory and/or executive function in healthy and impaired adults and children. However, the construct validity of performance measures on HPML tasks has not been established in healthy children. To assess the construct validity of measures of exploratory and rule-break errors on the Groton Maze Learning Task (GMLT) measures of spatial sequence memory (Corsi Blocks Task) and spatial error monitoring (Continuous Paired Associate Learning CPAL) were used. The results indicate that Corsi span predicted GMLT spatial sequence memory and CPAL accuracy predicted GMLT spatial error monitoring. The construct validity of the GMLT as a measure of spatial memory and executive function are discussed with regard to prior research using HPML tasks in neuropsychological contexts.
Publisher: Frontiers Media SA
Date: 22-12-2017
Publisher: No publisher found
No related grants have been discovered for Jacob Paul.