Patrick Cavanagh - Academia.edu (original) (raw)

Papers by Patrick Cavanagh

Introduction: why do we look at pictures? Artists have been looking at the world for thousands of... more Introduction: why do we look at pictures? Artists have been looking at the world for thousands of years, and thus paintings and drawings can be considered to form a  -year-old corpus of experimental psychology of perception. Through observation and trial-and-error they have exploited the principles of how our brains interpret the input from the retina, giving priority to only certain regularities of the visual pattern. Thus, a study of pictorial cues can tell us about the way that the brain recognizes objects, understands spatial depth, and uses illumination information in natural environments. Conversely, a better understanding of visual perception may help to explain the effectiveness of certain techniques used by artists. Therefore this essay will focus on some basic techniques in pictorial depiction that allow blobs of paint or charcoal marks to evoke objects, depth, movement, transparency, illumination, and refl ection. The development of these pictorial techniques by artists can be considered as fundamental discoveries about the neuroscience of perception.

Le système visuel a évolué de manière à prendre en compte les conséquences de nos mouvements sur ... more Le système visuel a évolué de manière à prendre en compte les conséquences de nos mouvements sur notre perception. L’évolution nous a particulièrement doté de la capacité à percevoir notre environnement visuel comme stable et continu malgré les importants déplacements de ses projections sur nos rétines à chaque fois que nous déplaçons nos yeux, notre tête ou notre corps. Des études chez l’animal ont récemment montré que dans certaines aires corticales et sous-corticales, impliquées dans le contrôle attentionnel et dans l’élaboration des mouvements oculaires, des neurones sont capables d’anticiper les conséquences des futurs mouvements volontaires des yeux sur leurs entrées visuelles. Ces neurones prédisent ce à quoi ressemblera notre environnement visuel en re-cartographiant la position des objets d’importance à l’endroit qu’ils occuperont après l’exécution d’une saccade. Dans une série d’études, nous avons tout d’abord démontré que cette re- cartographie pouvait être évaluée de man...

Computer vision, besides being a key area in Computer Science, is present in various industrial a... more Computer vision, besides being a key area in Computer Science, is present in various industrial applications, such as traffic sign recognition (including car license plates), face and gesture recognition , content-based image retrieval, remote sensing, cartography, radar sensing, and robot mapping. However, most computer vision systems disregard the cognitive aspects of human perception , thus limiting their applicability in natural environments, whereby small changes in the light conditions cause negative effects on the system's accuracy. This seminar brought together contributions from Computer Vision, Cognitive Psychology, Philosophy and History of Art in order to discuss the information content in cast shadows which, although currently recognised by psychologists as providing important cues about depth perception, is considered as noise in the computer vision literature. Seminar May 3-8, 2015-http://www.dagstuhl.de/15192

ABSTRACTTo capture where things are and what they are doing, the visual system may extract the po... more ABSTRACTTo capture where things are and what they are doing, the visual system may extract the position and motion of each object relative to its surrounding frame of referencee.g., 1,2. Here we report a particularly powerful example where a paradoxical stabilization is produced by a moving frame. We first take a frame that moves left and right and we flash its right edge before, and its left edge after, the frame’s motion. For all frame displacements tested, the two edges are perceived as stabilized, with the left edge on the left and right edge on the right, separated by the frame’s width as if the frame were not moving. This illusory stabilization holds even when the frame travels farther than its width, reversing the actual spatial order of the two flashes. Despite this stabilization, the motion of the frame is still seen, albeit much reduced, and this hides the paradoxical standstill of relative positions. In a second experiment, two probes are flashed inside the frame at the s...

Perception, 2021

The descriptions of surfaces, objects, and events computed by visual processes are not solely for... more The descriptions of surfaces, objects, and events computed by visual processes are not solely for consumption in the visual system but are meant to be passed on to other brain centers. Clearly, the description of the visual scene cannot be sent in its entirety, like a picture or movie, to other centers, as that would require that each of them have their own visual system to decode the description. Some very compressed, annotated, or labeled version must be constructed that can be passed on in a format that other centers—memory, language, planning—can understand. If this is a “visual language,” what is its grammar? In a first pass, we see, among other things, differences in processing of visual “nouns,” visual “verbs,” and visual “prepositions.” Then we look at recursion and errors of visual grammar. Finally, the possibility of a visual language also raises the question of the acquisition of its grammar from the visual environment and the chance that this acquisition process was borr...

Computer vision, besides being a key area in Computer Science, is present in various industrial a... more Computer vision, besides being a key area in Computer Science, is present in various industrial applications, such as traffic sign recognition (including car license plates), face and gesture recognition, content-based image retrieval, remote sensing, cartography, radar sensing, and robot mapping. However, most computer vision systems disregard the cognitive aspects of human perception, thus limiting their applicability in natural environments, whereby small changes in the light conditions cause negative effects on the system's accuracy. This seminar brought together contributions from Computer Vision, Cognitive Psychology, Philosophy and History of Art in order to discuss the information content in cast shadows which, although currently recognised by psychologists as providing important cues about depth perception, is considered as noise in the computer vision literature.

If a gabor pattern drifts in one direction while its internal texture drifts in the orthogonal di... more If a gabor pattern drifts in one direction while its internal texture drifts in the orthogonal direction, observers see a remarkable shift in its perceived direction when it is viewed in the periphery. The reported direction of the double-drift stimulus (also known as the infinite regress and curveball illusions) is some combination of the actual external motion of the gabor envelope and the internal motion of its texture (Tse & Hsieh, 2006). Here we find that if the observers track a fixation point that moves in tandem with the gabor, the illusion is undiminished. The pursuit of the moving fixation spot keeps the gabor roughly fixed at one location on the retina, cancelling its external motion, leaving only the internal motion. The gabor is seen to move in the world at roughly its actual speed as the motion of the eye is discounted at some point to recover velocities in world coordinates (e.g. Wallach, 1959). Our finding indicates that the combination of internal and external motio...

i-Perception

A random-dot background was expanded and contracted, and rotated, or expanded in one dimension wh... more A random-dot background was expanded and contracted, and rotated, or expanded in one dimension while contracting on the other, or skewed back and forth horizontally. Squares that were flashed at the reversal points of these affine pattern distortions, aligned to edges in the texture, showed massive changes in size and shape.

B1.01 Reversal of visual hemineglect: Differential influences of deactivating either contralatera... more B1.01 Reversal of visual hemineglect: Differential influences of deactivating either contralateral posterior parietal cortex or the superior colliculus.

Perception, 2016

An orbiting ray pattern produces an unexpected gray disk. Here we demonstrate this visual effect ... more An orbiting ray pattern produces an unexpected gray disk. Here we demonstrate this visual effect and its possible insights into visual temporal integration.

Journal of Vision, 2015

We investigated the influence of attention and motion on the sensitivity of flicker detection for... more We investigated the influence of attention and motion on the sensitivity of flicker detection for a target among distractors. Experiment 1 showed that when the target and distractors were moving, detection performance plummeted compared to when they were not moving, suggesting that the most sensitive detectors were local, temporal frequency-tuned receptive fields. With the stimuli in motion, a qualitatively different strategy was required and this led to much reduced performance. Cueing, which specified the target location with 100% validity, had no effect for targets that had little or no motion, suggesting that the flicker was sufficiently salient in this case to attract attention to the target without requiring any search. For targets with medium to high speeds, however, cueing provided a strong increase in sensitivity over uncued performance. This suggests a significant advantage for localizing and tracking the target and so sampling the luminance changes from only one trajectory. Experiment 2 showed that effect of attention was to increase the efficiency and duration of signal integration for the moving target. Overall, the results show that flicker sensitivity for a moving target relies on a much less efficient process than detection of static flicker, and that this less efficient process is facilitated when attention can select the relevant trajectory and ignore the others.

Motion detection can be achieved either with mechanisms sensitive to a target's velocity, or ... more Motion detection can be achieved either with mechanisms sensitive to a target's velocity, or sensitive to change in a target's position. Using a procedure to dissociate these two provided by Nakayama and Tyler (Vis Res 1981;21:427 -- 433), we explored detection of first-order (luminance-based) and various second-order (texture-based and stereo-based) motion. In the first experiment, observers viewed annular gratings oscillating in rotational motion at various rates. For each oscillation temporal frequency, we determined the minimum displacement of the pattern for which observers could reliably see motion. For first-order motion, these motion detection thresholds decreased with increasing temporal frequency, and thus were determined by a minimum velocity. In contrast, motion detection thresholds for second-order motion remained roughly constant across temporal frequency, and thus were determined by a minimum displacement. In Experiment 2, luminance-based gratings of different...

Journal of vision, 2015

Drawing involves frequent shifts of gaze between the original and the drawing and visual memory h... more Drawing involves frequent shifts of gaze between the original and the drawing and visual memory helps compare the original object and the drawing across these gaze shifts while creating and correcting the drawing. It remains unclear whether this memory encodes all of the object or only the features around the current drawing position and whether both the original and the copy are equally well represented. To address these questions, we designed a "drawing" experiment coupled with a change detection task. A polygon was displayed on one screen and participants had to copy it on another, with the original and the drawing presented in alternation. At unpredictable moments during the copying process, modifications were made on the drawing and the original figure (while they were not in view). Participants had to correct their drawing every time they perceived a change so that their drawing always matched the current original figure. Our results show a better memory representati...

Vision research, Jan 14, 2015

Object motion and position have long been thought to involve largely independent visual computati... more Object motion and position have long been thought to involve largely independent visual computations. However, the motion-induced position shift (Eagleman & Sejnowski, 2007) shows that the perceived position of a briefly presented static object can be influenced by nearby moving contours. Here we combine a particularly strong example of this illusion with a bistable global motion stimulus to compare the relative effects of global and component motion on the shift in perceived position. We used a horizontally oscillating diamond (Lorenceau & Shiffrar, 1992) that produces two possible global directions (left and right when fully visible versus up and down when vertices are occluded by vertical bars) as well as the oblique component motion orthogonal to each contour. To measure the motion-induced shift we flashed a test dot on the contour as the diamond reversed direction (Cavanagh & Anstis, 2013). Although the global motion had a highly significant influence on the direction and size ...

Any warning stimulus preceding a visual target generally leads to progressive reduction in respon... more Any warning stimulus preceding a visual target generally leads to progressive reduction in response times with increases in the warning-to-target temporal interval. This effect, called alerting, seems to be correlated with cortical activation. Three visuospatial cuing experiments were conducted with 10 non-neglecting left-brain-damaged patients in order to examine the possibility of an alerting impairment following lesions of the left hemisphere. Results indicate that large left-hemisphere lesions lead to a delay in the alerting effect of a warning signal for the processing of contralesional targets. Moreover, the results suggest that a lowered alerting state of the damaged hemisphere leads to a refractory difficulty in disengaging the focus of spatial attention from an invalidly cued ipsilesional location. Visual attention disorders are common after brain damage. Posner and collaborators, as well as other researchers, have made extensive use of the visuospatial cuing paradigm in documenting the nature of the selective attention deficits present in various brain-damaged populations (Ar

Introduction: why do we look at pictures? Artists have been looking at the world for thousands of... more Introduction: why do we look at pictures? Artists have been looking at the world for thousands of years, and thus paintings and drawings can be considered to form a  -year-old corpus of experimental psychology of perception. Through observation and trial-and-error they have exploited the principles of how our brains interpret the input from the retina, giving priority to only certain regularities of the visual pattern. Thus, a study of pictorial cues can tell us about the way that the brain recognizes objects, understands spatial depth, and uses illumination information in natural environments. Conversely, a better understanding of visual perception may help to explain the effectiveness of certain techniques used by artists. Therefore this essay will focus on some basic techniques in pictorial depiction that allow blobs of paint or charcoal marks to evoke objects, depth, movement, transparency, illumination, and refl ection. The development of these pictorial techniques by artists can be considered as fundamental discoveries about the neuroscience of perception.

Le système visuel a évolué de manière à prendre en compte les conséquences de nos mouvements sur ... more Le système visuel a évolué de manière à prendre en compte les conséquences de nos mouvements sur notre perception. L’évolution nous a particulièrement doté de la capacité à percevoir notre environnement visuel comme stable et continu malgré les importants déplacements de ses projections sur nos rétines à chaque fois que nous déplaçons nos yeux, notre tête ou notre corps. Des études chez l’animal ont récemment montré que dans certaines aires corticales et sous-corticales, impliquées dans le contrôle attentionnel et dans l’élaboration des mouvements oculaires, des neurones sont capables d’anticiper les conséquences des futurs mouvements volontaires des yeux sur leurs entrées visuelles. Ces neurones prédisent ce à quoi ressemblera notre environnement visuel en re-cartographiant la position des objets d’importance à l’endroit qu’ils occuperont après l’exécution d’une saccade. Dans une série d’études, nous avons tout d’abord démontré que cette re- cartographie pouvait être évaluée de man...

Computer vision, besides being a key area in Computer Science, is present in various industrial a... more Computer vision, besides being a key area in Computer Science, is present in various industrial applications, such as traffic sign recognition (including car license plates), face and gesture recognition , content-based image retrieval, remote sensing, cartography, radar sensing, and robot mapping. However, most computer vision systems disregard the cognitive aspects of human perception , thus limiting their applicability in natural environments, whereby small changes in the light conditions cause negative effects on the system's accuracy. This seminar brought together contributions from Computer Vision, Cognitive Psychology, Philosophy and History of Art in order to discuss the information content in cast shadows which, although currently recognised by psychologists as providing important cues about depth perception, is considered as noise in the computer vision literature. Seminar May 3-8, 2015-http://www.dagstuhl.de/15192

ABSTRACTTo capture where things are and what they are doing, the visual system may extract the po... more ABSTRACTTo capture where things are and what they are doing, the visual system may extract the position and motion of each object relative to its surrounding frame of referencee.g., 1,2. Here we report a particularly powerful example where a paradoxical stabilization is produced by a moving frame. We first take a frame that moves left and right and we flash its right edge before, and its left edge after, the frame’s motion. For all frame displacements tested, the two edges are perceived as stabilized, with the left edge on the left and right edge on the right, separated by the frame’s width as if the frame were not moving. This illusory stabilization holds even when the frame travels farther than its width, reversing the actual spatial order of the two flashes. Despite this stabilization, the motion of the frame is still seen, albeit much reduced, and this hides the paradoxical standstill of relative positions. In a second experiment, two probes are flashed inside the frame at the s...

Perception, 2021

The descriptions of surfaces, objects, and events computed by visual processes are not solely for... more The descriptions of surfaces, objects, and events computed by visual processes are not solely for consumption in the visual system but are meant to be passed on to other brain centers. Clearly, the description of the visual scene cannot be sent in its entirety, like a picture or movie, to other centers, as that would require that each of them have their own visual system to decode the description. Some very compressed, annotated, or labeled version must be constructed that can be passed on in a format that other centers—memory, language, planning—can understand. If this is a “visual language,” what is its grammar? In a first pass, we see, among other things, differences in processing of visual “nouns,” visual “verbs,” and visual “prepositions.” Then we look at recursion and errors of visual grammar. Finally, the possibility of a visual language also raises the question of the acquisition of its grammar from the visual environment and the chance that this acquisition process was borr...

Computer vision, besides being a key area in Computer Science, is present in various industrial a... more Computer vision, besides being a key area in Computer Science, is present in various industrial applications, such as traffic sign recognition (including car license plates), face and gesture recognition, content-based image retrieval, remote sensing, cartography, radar sensing, and robot mapping. However, most computer vision systems disregard the cognitive aspects of human perception, thus limiting their applicability in natural environments, whereby small changes in the light conditions cause negative effects on the system's accuracy. This seminar brought together contributions from Computer Vision, Cognitive Psychology, Philosophy and History of Art in order to discuss the information content in cast shadows which, although currently recognised by psychologists as providing important cues about depth perception, is considered as noise in the computer vision literature.

If a gabor pattern drifts in one direction while its internal texture drifts in the orthogonal di... more If a gabor pattern drifts in one direction while its internal texture drifts in the orthogonal direction, observers see a remarkable shift in its perceived direction when it is viewed in the periphery. The reported direction of the double-drift stimulus (also known as the infinite regress and curveball illusions) is some combination of the actual external motion of the gabor envelope and the internal motion of its texture (Tse & Hsieh, 2006). Here we find that if the observers track a fixation point that moves in tandem with the gabor, the illusion is undiminished. The pursuit of the moving fixation spot keeps the gabor roughly fixed at one location on the retina, cancelling its external motion, leaving only the internal motion. The gabor is seen to move in the world at roughly its actual speed as the motion of the eye is discounted at some point to recover velocities in world coordinates (e.g. Wallach, 1959). Our finding indicates that the combination of internal and external motio...

i-Perception

A random-dot background was expanded and contracted, and rotated, or expanded in one dimension wh... more A random-dot background was expanded and contracted, and rotated, or expanded in one dimension while contracting on the other, or skewed back and forth horizontally. Squares that were flashed at the reversal points of these affine pattern distortions, aligned to edges in the texture, showed massive changes in size and shape.

B1.01 Reversal of visual hemineglect: Differential influences of deactivating either contralatera... more B1.01 Reversal of visual hemineglect: Differential influences of deactivating either contralateral posterior parietal cortex or the superior colliculus.

Perception, 2016

An orbiting ray pattern produces an unexpected gray disk. Here we demonstrate this visual effect ... more An orbiting ray pattern produces an unexpected gray disk. Here we demonstrate this visual effect and its possible insights into visual temporal integration.

Journal of Vision, 2015

We investigated the influence of attention and motion on the sensitivity of flicker detection for... more We investigated the influence of attention and motion on the sensitivity of flicker detection for a target among distractors. Experiment 1 showed that when the target and distractors were moving, detection performance plummeted compared to when they were not moving, suggesting that the most sensitive detectors were local, temporal frequency-tuned receptive fields. With the stimuli in motion, a qualitatively different strategy was required and this led to much reduced performance. Cueing, which specified the target location with 100% validity, had no effect for targets that had little or no motion, suggesting that the flicker was sufficiently salient in this case to attract attention to the target without requiring any search. For targets with medium to high speeds, however, cueing provided a strong increase in sensitivity over uncued performance. This suggests a significant advantage for localizing and tracking the target and so sampling the luminance changes from only one trajectory. Experiment 2 showed that effect of attention was to increase the efficiency and duration of signal integration for the moving target. Overall, the results show that flicker sensitivity for a moving target relies on a much less efficient process than detection of static flicker, and that this less efficient process is facilitated when attention can select the relevant trajectory and ignore the others.

Motion detection can be achieved either with mechanisms sensitive to a target's velocity, or ... more Motion detection can be achieved either with mechanisms sensitive to a target's velocity, or sensitive to change in a target's position. Using a procedure to dissociate these two provided by Nakayama and Tyler (Vis Res 1981;21:427 -- 433), we explored detection of first-order (luminance-based) and various second-order (texture-based and stereo-based) motion. In the first experiment, observers viewed annular gratings oscillating in rotational motion at various rates. For each oscillation temporal frequency, we determined the minimum displacement of the pattern for which observers could reliably see motion. For first-order motion, these motion detection thresholds decreased with increasing temporal frequency, and thus were determined by a minimum velocity. In contrast, motion detection thresholds for second-order motion remained roughly constant across temporal frequency, and thus were determined by a minimum displacement. In Experiment 2, luminance-based gratings of different...

Journal of vision, 2015

Drawing involves frequent shifts of gaze between the original and the drawing and visual memory h... more Drawing involves frequent shifts of gaze between the original and the drawing and visual memory helps compare the original object and the drawing across these gaze shifts while creating and correcting the drawing. It remains unclear whether this memory encodes all of the object or only the features around the current drawing position and whether both the original and the copy are equally well represented. To address these questions, we designed a "drawing" experiment coupled with a change detection task. A polygon was displayed on one screen and participants had to copy it on another, with the original and the drawing presented in alternation. At unpredictable moments during the copying process, modifications were made on the drawing and the original figure (while they were not in view). Participants had to correct their drawing every time they perceived a change so that their drawing always matched the current original figure. Our results show a better memory representati...

Vision research, Jan 14, 2015

Object motion and position have long been thought to involve largely independent visual computati... more Object motion and position have long been thought to involve largely independent visual computations. However, the motion-induced position shift (Eagleman & Sejnowski, 2007) shows that the perceived position of a briefly presented static object can be influenced by nearby moving contours. Here we combine a particularly strong example of this illusion with a bistable global motion stimulus to compare the relative effects of global and component motion on the shift in perceived position. We used a horizontally oscillating diamond (Lorenceau & Shiffrar, 1992) that produces two possible global directions (left and right when fully visible versus up and down when vertices are occluded by vertical bars) as well as the oblique component motion orthogonal to each contour. To measure the motion-induced shift we flashed a test dot on the contour as the diamond reversed direction (Cavanagh & Anstis, 2013). Although the global motion had a highly significant influence on the direction and size ...

Any warning stimulus preceding a visual target generally leads to progressive reduction in respon... more Any warning stimulus preceding a visual target generally leads to progressive reduction in response times with increases in the warning-to-target temporal interval. This effect, called alerting, seems to be correlated with cortical activation. Three visuospatial cuing experiments were conducted with 10 non-neglecting left-brain-damaged patients in order to examine the possibility of an alerting impairment following lesions of the left hemisphere. Results indicate that large left-hemisphere lesions lead to a delay in the alerting effect of a warning signal for the processing of contralesional targets. Moreover, the results suggest that a lowered alerting state of the damaged hemisphere leads to a refractory difficulty in disengaging the focus of spatial attention from an invalidly cued ipsilesional location. Visual attention disorders are common after brain damage. Posner and collaborators, as well as other researchers, have made extensive use of the visuospatial cuing paradigm in documenting the nature of the selective attention deficits present in various brain-damaged populations (Ar