Papers by William Beaudot
Scientific reports, Jan 21, 2017
Vestibular-somatosensory interactions are pervasive in the brain but it remains unclear why. Here... more Vestibular-somatosensory interactions are pervasive in the brain but it remains unclear why. Here we explore the contribution of tactile flow to processing self-motion. We assessed two aspects of self-motion: timing and speed. Participants sat on an oscillating swing and either kept their hands on their laps or rested them lightly on an earth-stationary surface. They viewed a grating oscillating at the same frequency as their motion and judged its phase or, in a separate experiment, its speed relative to their perceived motion. Participants required the phase to precede body movement (with or without tactile flow) or tactile flow by ~5° (44 ms) to appear earth-stationary. Speed judgments were 4-10% faster when motion was from tactile flow, either alone or with body motion, compared to body motion alone (where speed judgments were accurate). By comparing response variances we conclude that phase and speed judgments do not reflect optimal integration of tactile flow with other cues to...
i-Perception
We describe a mobile app that measures early cortical visual processing suitable for use in clini... more We describe a mobile app that measures early cortical visual processing suitable for use in clinics. The app is called Component Extraction and Motion Integration Test (CEMIT). Observers are asked to respond to the direction of translating plaids that move in one of two very different directions. The plaids have been selected so that the plaid components move in one of the directions and the plaid pattern moves in the other direction. In addition to correctly responding to the pattern motion, observers demonstrate their ability to correctly extract the movement (and therefore the orientation) of the underlying components at specific spatial frequencies. We wanted to test CEMIT by seeing if we could replicate the broader tuning observed at low spatial frequencies for this type of plaid. Results from CEMIT were robust and successfully replicated this result for 50 typical observers. We envisage that it will be of use to researchers and clinicians by allowing them to investigate specif...
Nous présentons dans cet article un modèle de réseau de neurones issu d'études faites sur le ... more Nous présentons dans cet article un modèle de réseau de neurones issu d'études faites sur le traitement du signal dans les systèmes biologiques. Ces travaux nous ont permis de trouver un modèle de réseau de neurones à deux couches de filtres, qui possède des propriétés de filtrage particulièrement intéressantes en traitement du signal bidimensionnel et notamment pour l'analyse d'objets en mouvement dans des séquences d'images. Ce traitement analogique du signal permet un filtrage temporel continu performant tout en facilitant la réalisation d'un circuit à faible consommation d'énergie. Nous présentons le modèle de réseau utilisé, ses propriétés au sens du filtrage d'images et les résultats obtenus sur des séquences d'images ainsi qu'une étude de faisabilité VLSI en vue de la réalisation d'une rétine pour caméra, sensible aux mouvements.
15° Colloque sur le …, Jan 1, 1995
8ibnes Joumies NEUROSCIENCES ET …, Jan 1, 1996
Citeseer
We propose a theoretical framework of the adaptive control of visual sensitivity performed by the... more We propose a theoretical framework of the adaptive control of visual sensitivity performed by the vertebrate retina. Instead of a logarithmic function, the photoreceptor transfer function is modelled with a Michaelis-Menten law which has a more plausible biophysical correlate. We show that the neural and functional architecture of the retina supports the requirements for an optimal transcoding of non-stationary visual information: This control of visual sensitivity is done by using an adaptive transfer function whose parameters are spatiotemporally and locally estimated by the subsequent retinal circuit and fed back at the level of photoreceptors. Although the use of the resulting model remains limited in the context of digital image processing, it provides a good structural framework for an analog VLSI implementation of an adaptive spatiotemporal neuromorphic retina.
In this paper, we first review the most common neurodegenerative diseases and mental disorders, a... more In this paper, we first review the most common neurodegenerative diseases and mental disorders, and their effects on visual functions. Secondly, we present Psykinematix, a new Mac OS X software package dedicated to visual psychophysics. Because it does not require any programming skill, and provides an intuitive GUI that abstracts most of the inherent difficulties, this new tool provides effortless means to create and run the complex psychophysical paradigms developed by vision scientists. Finally, we discuss how Psykinematix could help clinician researchers replicate fundamental studies, and better investigate visual functions that are impaired by aging and neural dysfunctions, such as shape and motion processing.
wbeaudot.kybervision.com
These results suggest that: 1) The three postreceptoral mechanisms use a common contour integrati... more These results suggest that: 1) The three postreceptoral mechanisms use a common contour integration process. This linking process, however, cannot be colorblind, as we also showed that linking between different chromatic mechanisms or between opposite spatial phases disrupts contour integration [3,6], and thus it must remain sensitive to the color contrast and phase of its inputs. 2) Color vision is somewhat impaired on the global shape discrimination task, and may be limited by a broader orientation tuning at some early cortical stages and/or be more reliant on local cues at the integration stages. DISCUSSION Overall, these experiments demonstrate that color vision is only slightly worse than luminance vision when pre-cortical factors are taken into account such as contrast sensitivity and spatio-temporal resolutions, and suggest that color vision has sufficient orientation selectivity and processing capabilities to perform basic 2D shape perception. These experiments also support the recent neurophysiological finding that chromatic and luminance pathways share significant computational resources in V1 in a way suitable for shape perception [8-9].
wbeaudot.kybervision.net
Contour integration is strongly primed by path elements: i) pathfirst performance is already opti... more Contour integration is strongly primed by path elements: i) pathfirst performance is already optimal for the shortest duration (13ms), while background-first and synchronous performances rise smoothly with stimulus duration; ii) the shortest delay (13 ms) is as effective as the longest for path-first, while longer delays boost the performance for background-first; iii) synchronous performances are generally lower than background-first performances, rise even more slowly, and cannot compensate, at the same total duration, for the gain in path-first performance. 2) Facilitation depends on the asynchrony order in the first cycle: i) performance rises smoothly with stimulus duration until reaching an asymptotic level; ii) both asynchronous conditions show a slight advantage below 100 ms, while path-first performance is significantly higher (by about 10%) only above 100 ms; iii) background-first and synchronous performances saturate at the same level.
Evidence that visual grouping is facilitated when elements comprising a foreground figure are pre... more Evidence that visual grouping is facilitated when elements comprising a foreground figure are presented simultaneously, and are temporally separated from elements comprising the background, has suggested cortical synchronous oscillations as a possible neural substrate. Supporting this theory, Usher and Donnelly (Nature 394 (1998) 179) showed in one of their experiments that contour integration is facilitated when path and background elements alternate with an asynchrony below the integration time of the visual system, suggesting that these flickering stimuli interact with this hypothetical binding mechanism. I replicated this experiment and report that the effect depends in fact on the order of asynchrony between path and background elements in the first cycle of stimuli presented for more than 100 ms: facilitation in visual grouping only occurs when path elements are presented before background elements. A second experiment, exploring the effect of onset delays between path and background elements, demonstrates a strong priming effect of path elements. I conclude that Usher and Donnelly's result is likely due to the high sensitivity of the visual system to stimulus onset, and that simple flickering stimuli are inadequate for revealing the neural code for binding in figure-ground segregation without controlling for the effect of stimulus onset.
Journal of Vision, Jan 1, 2001
Journal of Vision, Jan 1, 2003
… sur le traitement du signal et …, Jan 1, 1993
Journal of Vision, Jan 1, 2011
In studies of shape processing, a crucial distinction is made between the global stages, which in... more In studies of shape processing, a crucial distinction is made between the global stages, which integrate across features to define shape, and earlier stages that encode individual components. We investigate whether shape discrimination thresholds for radial frequency (RF) patterns are limited at this global stage or whether the information in individual components supports threshold. We use achromatic and chromatic (L/M-and S-cone opponent) radial frequency (RF) patterns of different contour thicknesses (0.75-6 cpd). First, we show using sections of an RF4 that shape discrimination thresholds are invariant with cycle number from 1 to the complete pattern. Performance for a single cycle displayed alone is as good as for the whole RF, indicating that information within a single RF cycle is sufficient to support the whole shape discrimination threshold, arguing against an influence of global processing. Second, we find similar thresholds for the discrimination of RF patterns and modulated line stimuli, also arguing against global effects. Third, we calculate a metric for the intrinsic orientation variation in a stimulus cycle at threshold and show that this potentially accounts for the improvement in shape and line discrimination thresholds with modulation frequency from RF1 to RF6. Higher threshold discrimination for chromatic compared to achromatic patterns may reflect the poorer orientation discrimination of color vision, rather than a deficit for global processing. We propose that the global stages of shape processing are not revealed at threshold but are enabled only for well-defined shapes at suprathreshold modulations.
Image Processing, 1996. Proceedings., …, Jan 1, 1996
We propose a theoretical framework of the adaptive control of visual sensitivity performed by the... more We propose a theoretical framework of the adaptive control of visual sensitivity performed by the vertebrate retina. Instead of a logarithmic function, the photoreceptor transfer function is modelled with a Michaelis-Menten law which has a more plausible biophysical correlate. We show that the neural and functional architecture of the retina supports the requirements for an optimal transcoding of non-stationary visual information: This control of visual sensitivity is done by using an adaptive transfer function whose parameters are spatiotemporally and locally estimated by the subsequent retinal circuit and fed back at the level of photoreceptors. Although the use of the resulting model remains limited in the context of digital image processing, it provides a good structural framework for an analog VLSI implementation of an adaptive spatiotemporal neuromorphic retina.
PERCEPTION-LONDON-, Jan 1, 2000
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Papers by William Beaudot