Kevin R Brooks
Macquarie University, Department of Psychology, Faculty Member
Research Interests:
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Body image disturbance – a cause of distress amongst the general population and those diagnosed with various disorders – is often attributed to the media’s unrealistic depiction of ideal bodies. These ideals are strongly gendered, leading... more
Body image disturbance – a cause of distress amongst the general population and those diagnosed with various disorders – is often attributed to the media’s unrealistic depiction of ideal bodies. These ideals are strongly gendered, leading to pronounced fat concern amongst females, and a male preoccupation with muscularity. Recent research suggests that visual aftereffects may be fundamental to the misperception of body fat and muscle mass – the perceptual component of body image disturbance. This study sought to establish the influence of gender on these body aftereffects. Male and female observers were randomly assigned to one of four adaptation conditions (low fat, high fat, low muscle, and high muscle bodies) and were asked to adjust the apparent fat and muscle levels of male and female bodies to make them appear as ‘normal’ as possible both before and after adaptation. While neither the gender of observers or of body stimuli had a direct effect, aftereffect magnitude was signifi...
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Research has previously shown that adding consistent stereoscopic information to self-motion displays can improve the vection in depth induced in physically stationary observers. In some past studies, the simulated eye-separation was... more
Research has previously shown that adding consistent stereoscopic information to self-motion displays can improve the vection in depth induced in physically stationary observers. In some past studies, the simulated eye-separation was always close to the observer's actual eye-separation, as the aim was to examine vection under ecological viewing conditions that provided consistent binocular and monocular self-motion information. The present study investigated whether large discrepancies between the observer's simulated and physical eye-separations would alter the vection-inducing potential of stereoscopic optic flow (either helping, hindering, or preventing the induction of vection). Our self-motion displays simulated eye-separations of 0 cm (the non-stereoscopic control), 3.25 cm (reduced from normal), 6.5 cm (approximately normal), and 13 cm (exaggerated relative to normal). The rated strength of vection in depth was found to increase systematically with the simulated eye-s...
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Research Interests: Psychology, Cognitive Science, Psychophysics, Perception, Psychophysics of vision, and 15 moreVisual perception, Binocular vision, Motion perception, Stereopsis, Trajectory, Humans, Depth Perception, Female, Male, Adult, Motion in depth, Stereomotion, Motion Aftereffect, Monocular Vision, and Random Allocation
Laboratory-based studies of perceived speed show that, under most circumstances, perceived speed is reduced as a function of contrast. However, a recent investigation of perceived vehicular speed while driving around a closed road circuit... more
Laboratory-based studies of perceived speed show that, under most circumstances, perceived speed is reduced as a function of contrast. However, a recent investigation of perceived vehicular speed while driving around a closed road circuit showed no such effect (Owens, Wood, & Carberry, 2010, Perception, 39: , 1199-1215). We sought to probe the source of this discrepancy, asking whether the presence or absence of stereoscopic motion information might account for the difference in results. In a two-alternative forced-choice psychophysical speed-discrimination task, observers compared the speed of high- and low-contrast driving clips filmed with a 3-D camera and presented either stereoscopically (3-D) or monoscopically (2-D). Although perceived speed was reduced at low contrast, the size of this misperception was equivalent for 2-D and 3-D presentations. However, the inclusion of stereoscopic cues to vehicular speed caused significant improvements in the precision of speed judgments. It is concluded that although stereopsis can provide access to valuable information on perceived speed, contrast-independent speed estimation as demonstrated by Owens et al. (2010) is more likely to reflect the use of the full visual field in a real driving situation (compared with limited field of view simulations), or the additional contributions of nonvisual cues rather than stereopsis.
Research Interests: Psychology, Cognitive Science, Perception, Visual perception, Motion perception, and 15 moreHuman Factors in Visual Perception, Humans, Depth Perception, Female, Male, Young Adult, Driving Simulation, Vection, Adult, Graphic Driving Simulator, Speed Perception, Driving Simulators, Egomotion, Automobile driving, and Psychomotor Performance
Stereomotion (binocularly specified motion-in-depth) studies have established the existence of several cues to speed. For binocular features, cues involve (a) changes in disparity over time ('changing disparity', CD), or (b)... more
Stereomotion (binocularly specified motion-in-depth) studies have established the existence of several cues to speed. For binocular features, cues involve (a) changes in disparity over time ('changing disparity', CD), or (b) differences in the velocities of features between the eyes ('interocular velocity difference', IOVD). Although the precision of these has been studied, their accuracy has not. We performed a 2AFC stereomotion speed discrimination experiment (N= 4) to ascertain the relative perceived speed of RDS (CD and IOVD cues) ...
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The history of the expression of three-dimensional structure in art can be traced from the use of occlusion in Palaeolithic cave paintings, through the use of shadow in classical art, to the development of perspective during the... more
The history of the expression of three-dimensional structure in art can be traced from the use of occlusion in Palaeolithic cave paintings, through the use of shadow in classical art, to the development of perspective during the Renaissance. However, the history of the use of stereoscopic techniques is controversial. Although the first undisputed stereoscopic images were presented by Wheatstone in 1838, it has been claimed that two sketches by Jacopo Chimenti da Empoli (c. 1600) can be to be fused to yield an impression of stereoscopic depth, while others suggest that Leonardo da Vinci's Mona Lisa is the world's first stereogram. Here, we report the first quantitative study of perceived depth in these works, in addition to more recent works by Salvador Dalí. To control for the contribution of monocular depth cues, ratings of the magnitude and coherence of depth were recorded for both stereoscopic and pseudoscopic presentations, with a genuine contribution of stereoscopic cues revealed by a difference between these scores. Although effects were clear for Wheatstone and Dalí's images, no such effects could be found for works produced earlier. As such, we have no evidence to reject the conventional view that the first producer of stereoscopic imagery was Sir Charles Wheatstone.
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Prolonged exposure to images of narrow bodies has been shown to induce a perceptual 18 aftereffect, such that observers’ point of subjective normality (PSN) for bodies shifts towards 19 narrower bodies. The converse effect is shown for... more
Prolonged exposure to images of narrow bodies has been shown to induce a perceptual
18 aftereffect, such that observers’ point of subjective normality (PSN) for bodies shifts towards
19 narrower bodies. The converse effect is shown for adaptation to wide bodies. In low-level
20 stimuli, object attention (attention directed to the object) and spatial attention (attention
21 directed to the location of the object) have been shown to increase the magnitude of visual
22 aftereffects, while object-based attention enhances the adaptation effect in faces. It is not
23 known whether featural attention (attention directed to a specific aspect of the object) affects
24 the magnitude of adaptation effects in body stimuli. Here, we manipulate the attention of
25 Caucasian observers to different featural information in body images, by asking them to rate
26 the fatness or sex typicality of male and female bodies manipulated to appear fatter or thinner
27 than average. PSNs for body fatness were taken at baseline and after adaptation, and a change
28 in PSN (ΔPSN) was calculated. A body size adaptation effect was found, with observers who
29 viewed fat bodies showing an increased PSN, and those exposed to thin bodies showing a
30 reduced PSN. However, manipulations of featural attention to body fatness or sex typicality
31 produced equivalent results, suggesting that featural attention may not affect the strength of
32 the body size aftereffect.
18 aftereffect, such that observers’ point of subjective normality (PSN) for bodies shifts towards
19 narrower bodies. The converse effect is shown for adaptation to wide bodies. In low-level
20 stimuli, object attention (attention directed to the object) and spatial attention (attention
21 directed to the location of the object) have been shown to increase the magnitude of visual
22 aftereffects, while object-based attention enhances the adaptation effect in faces. It is not
23 known whether featural attention (attention directed to a specific aspect of the object) affects
24 the magnitude of adaptation effects in body stimuli. Here, we manipulate the attention of
25 Caucasian observers to different featural information in body images, by asking them to rate
26 the fatness or sex typicality of male and female bodies manipulated to appear fatter or thinner
27 than average. PSNs for body fatness were taken at baseline and after adaptation, and a change
28 in PSN (ΔPSN) was calculated. A body size adaptation effect was found, with observers who
29 viewed fat bodies showing an increased PSN, and those exposed to thin bodies showing a
30 reduced PSN. However, manipulations of featural attention to body fatness or sex typicality
31 produced equivalent results, suggesting that featural attention may not affect the strength of
32 the body size aftereffect.
Although research addressing body size misperception has focused on socio-cognitive processes, such as internalization of the " ideal " images of bodies in the media, the perceptual basis of this phenomenon remains largely unknown.... more
Although research addressing body size misperception has focused on socio-cognitive processes, such as internalization of the " ideal " images of bodies in the media, the perceptual basis of this phenomenon remains largely unknown. Further, most studies focus on body size per se even though this depends on both fat and muscle mass – variables that have very different relationships with health. We tested visual adaptation as a mechanism for inducing body fat and muscle mass misperception, and assessed whether these two dimensions of body space are processed independently. Observers manipulated the apparent fat and muscle mass of bodies to make them appear " normal " before and after inspecting images from one of four adaptation conditions (increased fat/decreased fat/increased muscle/decreased muscle). Exposure resulted in a shift in the point of subjective normality in the direction of the adapting images along the relevant (fat or muscle) axis, suggesting that the neural mechanisms involved in body fat and muscle perception are independent. This supports the viability of adaptation as a model of real-world body size misperception, and extends its applicability to clinical manifestations of body image disturbance that entail not only preoccupation with thinness (e.g., anorexia nervosa) but also with muscularity (e.g., muscle dysmorphia). Body size misperception is a phenomenon wherein people believe themselves or others to be larger or smaller than they actually are 1–3. In research conducted in a broad range of populations, and in both adolescents and adults, as many as half of participants have been found to misperceive their body weight 4–8. This is concerning in two respects 3. First, individuals who are underweight or normal-weight according to accepted classifications but who believe themselves to be overweight are likely to have high levels of body dissatisfaction and, in turn, increased risk of mental health problems such as eating disorders, anxiety and depression 9–11. Further, a recent study involving a multisensory illusion induced using a virtual reality setup has shown a causal link between changes in perceived body size and changes in body dissatisfaction 12. Conversely, individuals who are overweight or obese but who believe themselves to be of normal or otherwise acceptable weight may be less motivated to make efforts to reduce body weight, and less likely to seek help for obesity-related medical problems 6,8,13. To date, research addressing body size misperception has tended to focus on socio-cognitive processes, such as internalization of the " ideal " images of male and female bodies portrayed in the popular media 7,14,15 or, in the case of underestimation of body size among overweight individuals, increased exposure to obesity in everyday life and a consequent change in what is considered a " normal and healthy " body weight 3,8,16. As a consequence, little is known about the perceptual mechanisms underpinning body size misperception. However, there is growing
Research Interests: Psychophysics, Perception, Psychophysics of vision, Human Perception and Performance, Eating Disorders, and 19 moreVisual perception, Adaptation, Body Image, Eating Disorders and Body Image, Muscle Dysmorphia, Body Image (Psychology), Eating Disorders and Obesity, Male body image, Body dysmorphic disorder, Adaptation Aftereffects, Aftereffect, Psychology of Visual Perception, Mass media and body image, Mass Media and the Effects on Body Image, Visual Psychophysics, Body Image Satisfaction, Male Eating Disorders, Body Dysmorphia, and Muscle Dysmorphia An Underrecognized Form of Body Dysmorphic Disorde
The perception of speed is susceptible to manipulations of image contrast, both for simple sine wave and more complex stimuli, such that low-contrast patterns generally appear slower than their high-contrast equivalents. It is not known... more
The perception of speed is susceptible to manipulations of image contrast, both for simple sine wave and more complex stimuli, such that low-contrast patterns generally appear slower than their high-contrast equivalents. It is not known whether the crucial factor is the contrast of the underlying Fourier components or the contrast of the overall complex pattern. Here, two experiments investigate this issue using compound gratings, comprising two vertical sine wave stimuli with equal contrast, but a 3:1 spatial frequency ratio. Component gratings were summed in ''peaks add'' and in ''peaks subtract'' phase, creating conditions with either (a) identical component contrasts, despite differences in overall pattern contrast or (b) differences in component contrasts despite identical overall pattern contrast. Experiment 1 demonstrated that the perceived speed is determined by the contrast of the components regardless of relative phase and hence of overall pattern contrast. Experiment 2 replicated this result while eliminating potential explanations based on differences in spatial frequency content. Along with previous compound grating and plaid studies, the data support a two-stage velocity estimation process involving the derivation of separate speed signals for each Fourier component, followed by integration of these signals across spatial scales. Creative Commons CC-BY: This article is distributed under the terms of the Creative Commons Attribution 3.0 License (http://www.creativecommons.org/licenses/by/3.0/) which permits any use, reproduction and distribution of the work without further permission provided the original work is attributed as specified on the SAGE and Open Access pages (https://us.sage-pub.com/en-us/nam/open-access-at-sage).
Research Interests:
Prolonged exposure to images of narrow bodies has been shown to induce a perceptual aftereffect, such that observers' point of subjective normality (PSN) for bodies shifts toward narrower bodies. The converse effect is shown for... more
Prolonged exposure to images of narrow bodies has been shown to induce a perceptual aftereffect, such that observers' point of subjective normality (PSN) for bodies shifts toward narrower bodies. The converse effect is shown for adaptation to wide bodies. In low-level stimuli, object attention (attention directed to the object) and spatial attention (attention directed to the location of the object) have been shown to increase the magnitude of visual aftereffects, while object-based attention enhances the adaptation effect in faces. It is not known whether featural attention (attention directed to a specific aspect of the object) affects the magnitude of adaptation effects in body stimuli. Here, we manipulate the attention of Caucasian observers to different featural information in body images, by asking them to rate the fatness or sex typicality of male and female bodies manipulated to appear fatter or thinner than average. PSNs for body fatness were taken at baseline and after adaptation, and a change in PSN (PSN) was calculated. A body size adaptation effect was found, with observers who viewed fat bodies showing an increased PSN, and those exposed to thin bodies showing a reduced PSN. However, manipulations of featural attention to body fatness or sex typicality produced equivalent results, suggesting that featural attention may not affect the strength of the body size aftereffect.
Research Interests: Psychophysics, Psychophysics of vision, Visual attention, Visual perception, Attention (Psychology), and 8 moreBody Image, Eating Disorders and Body Image, Visual Attention (Psychology), Body Image (Psychology), Adaptation Aftereffects, Media and Body Image, Visual Psychophysics, and Body Image Satisfaction
Counter-terrorism and crime prevention often depend on our ability to match images of unfamiliar faces. For example, when issuing passports, staff must establish an applicant's identity by comparing the submitted photograph witht those in... more
Counter-terrorism and crime prevention often depend on our ability to match images of unfamiliar faces. For example, when issuing passports, staff must establish an applicant's identity by comparing the submitted photograph witht those in the database of current passports to ensure that multiple documents are not issued to the same person under different names. Previous research has shown that this is a difficult and error prone task. We suggest that this 'passport problem' may be due to an over-reliance on the appearance of external facial features that can be unreliable cues to identity. Compatible with this explanation, we demonstrate that in difficult trials involving a change of appearance or attempted fraud involving a similar looking foil, participants are better able to determine whether two images are of the same person when shown only the internal features of the faces rather than whole images. This discovery has significant practical implications and could form the basis of a procedure to improve the detection of identity fraud.
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PURPOSE. A clinical diagnosis of stereoblindness does not necessarily preclude compelling depth perception. Qualitative observations suggest that this may be due to the dynamic nature of the stimuli. The purpose of this study was to... more
PURPOSE. A clinical diagnosis of stereoblindness does not necessarily preclude compelling depth perception. Qualitative observations suggest that this may be due to the dynamic nature of the stimuli. The purpose of this study was to systematically investigate the effectiveness of static and dynamic stereoscopic stimuli. METHODS. Stereoscopic stimuli were presented on a passive polarized stereoscopic monitor and were manipulated as follows: static disparity (baseline condition), dynamic disparity (change in z-location), change in stimulus pattern, change in z-location with pattern change, change in x-location (horizontal shift), a control (nil-disparity signal). All depth-detection thresholds were measured simultaneously using an adaptive four-alternative-forced-choice (4AFC) paradigm with all six conditions randomly interleaved. RESULTS. A total of 127 participants (85 women, 42 men; mean [SD] age, 21 [5] years) with visual acuity better than 0.22 logMAR in both eyes were assessed. In comparison to the static disparity condition, depth-detection thresholds were up to 50% lower for the dynamic disparity conditions, with and without pattern change (P < 0.001). The presence of a changing pattern in isolation (P ¼ 0.71) or a horizontal shift (P ¼ 0.41) did not affect the thresholds. CONCLUSIONS. Dynamic disparity information facilitates the extraction of depth in comparison to static disparity signals. This finding may account for the compelling perception of depth reported in individuals with no measurable static stereoacuity. Our findings challenge the traditional definition of stereoblindness and suggest that current diagnostic tests using static stimuli may be suboptimal. We argue that both static and dynamic stimuli should be employed to fully assess the binocular potential of patients when considering management options.
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Body size misperception is common amongst the general public and is a core component of eating disorders and related conditions. While perennial media exposure to the " thin ideal " has been blamed for this misperception, relatively... more
Body size misperception is common amongst the general public and is a core component of eating disorders and related conditions. While perennial media exposure to the " thin ideal " has been blamed for this misperception, relatively little research has examined visual adaptation as a potential mechanism. We examined the extent to which the bodies of "self" and "other" are processed by common or separate mechanisms in young women. Using a contingent adaptation paradigm, experiment 1 gave participants prolonged exposure to images both of the self and of another female that had been distorted in opposite directions (e.g., expanded other/contracted self), and assessed the aftereffects using test images both of the self and other. The directions of the resulting perceptual biases were contingent on the test stimulus, establishing at least some separation between the mechanisms encoding these body types. Experiment 2 used a cross adaptation paradigm to further investigate the extent to which these mechanisms are independent. Participants were adapted either to expanded or to contracted images of their own body or that of another female. While adaptation effects were largest when adapting and testing with the same body type, confirming the separation of mechanisms reported in experiment 1, substantial misperceptions were also demonstrated for cross adaptation conditions, demonstrating a degree of overlap in the encoding of self and other. In addition, the evidence of misperception of one's own body following exposure to " thin " and to " fat " others demonstrates the viability of visual adaptation as a model of body image disturbance both for those who underestimate and those who overestimate their own size.
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The dominant evolutionary theory of physical attraction posits that attractiveness reflects physiological health, and attraction is a mechanism for identifying a healthy mate. Previous studies have found that perceptions of the healthiest... more
The dominant evolutionary theory of physical attraction posits that attractiveness reflects physiological health, and attraction is a mechanism for identifying a healthy mate. Previous studies have found that perceptions of the healthiest body mass index (weight scaled for height; BMI) for women are close to healthy BMI guidelines, while the most attractive BMI is significantly lower, possibly pointing to an influence of sociocultural factors in determining attractive BMI. However, less is known about ideal body size for men. Further, research has not addressed the role of body fat and muscle, which have distinct relationships with health and are conflated in BMI, in determining perceived health and attractiveness. Here, we hypothesised that, if attractiveness reflects physiological health, the most attractive and healthy appearing body composition should be in line with physiologically healthy body composition. Thirty female and 33 male observers were instructed to manipulate 15 female and 15 male body images in terms of their fat and muscle to optimise perceived health and, separately, attractiveness. Observers were unaware that they were manipulating the muscle and fat content of bodies. The most attractive apparent fat mass for female bodies was significantly lower than the healthiest appearing fat mass (and was lower than the physiologically healthy range), with no significant difference for muscle mass. The optimal fat and muscle mass for men's bodies was in line with the healthy range. Male observers preferred a significantly lower overall male body mass than did female observers. While the body fat and muscle associated with healthy and attractive appearance is broadly in line with physiologically healthy values, deviations from this pattern suggest that future research should examine a possible role for internalization of body ideals in influencing perceptions of attractive body composition, particularly in women.
Research Interests: Evolutionary Psychology, Body Image, Health, Male body image, Drive for Muscularity and Body Dissatisfaction Among Athletes and Non Athletes, and 8 morePercentage of body fat (PBF), Drive for Muscularity, Body Image, Body Fat, Physical Attractiveness, Muscularity-oriented Disordered Eating, Body Image Between Males and Females, Body fat percentage, and Muscularity
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Research Interests: Psychology, Cognitive Science, Psychophysics, Perception, Photography, and 13 morePsychophysics of vision, Visual perception, Face recognition (Psychology), Adolescent, Visual perception (Psychology), Humans, Body perception, Form perception, Female, Young Adult, Waist to Hip Ratio, Adult, and Body Shape
Research Interests: Bioinformatics, Computer Vision, Visual perception, Computational Neuroscience, Life Sciences, and 16 moreMachine Vision, Model, Biomedical Research, Illusions, Illusion, Cortex, Optical Illusions, Visual, Muller-Lyer illusion, Computational, Clinical Sciences, Computational Cognitive Neuroscience, Computational neurosciences, Computational/ Interdisciplinary Neuroscience, HMAX Model, and Neurosciences
Abstract To examine the spatial scale of the mechanism supporting the perception of motion-in-depth defined by binocular disparity cues, we measured stereomotion speed discrimination thresholds as a function of stimulus width using a 2IFC... more
Abstract To examine the spatial scale of the mechanism supporting the perception of motion-in-depth defined by binocular disparity cues, we measured stereomotion speed discrimination thresholds as a function of stimulus width using a 2IFC paradigm. Dynamic random dot stereogram bars, wherein new but perfectly binocularly correlated dot arrays are presented interleaved at a rate of 120Hz per eye, were displayed using ferro-electric shutter glasses on a 240Hz fast-phosphor monitor. Frame-by-frame manipulation of disparity ...
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Abstract Slanted surfaces are often seen against backgrounds or through apertures. In addition to providing a binocular context, such conditions result in the presence of monocular regions (sidebands) at the side of the binocularly... more
Abstract Slanted surfaces are often seen against backgrounds or through apertures. In addition to providing a binocular context, such conditions result in the presence of monocular regions (sidebands) at the side of the binocularly slanted surface whose locations and/or relative widths could provide information about slant independent of azimuth, distance to the slanted surface, distance between surface and background/aperture or width of the slanted surface. Sidebands can be either temporal on each eye ( ...
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Abstract Stereomotion experiments often feature monocularly visible stimuli. When such stimuli move in depth, different monocular motion signals are presented simultaneously to each eye. Though this &amp;amp;#x27;inter-ocular velocity... more
Abstract Stereomotion experiments often feature monocularly visible stimuli. When such stimuli move in depth, different monocular motion signals are presented simultaneously to each eye. Though this &amp;amp;#x27;inter-ocular velocity difference&amp;amp;#x27;cue to stereomotion has been investigated in a number of studies, the observed behaviour could theoretically have been based on properties of an individual monocular image. To isolate such potential artifacts, we performed a 2IFC speed-discrimination task using random dot stereograms moving either ...
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Abstract Howard and Duke (Vision Research, 2003) generated binocular displays that contained a grey transparent square offset from a vertical bar in one eye, and a vertical bar with a gap in the other eye. Observers perceived a... more
Abstract Howard and Duke (Vision Research, 2003) generated binocular displays that contained a grey transparent square offset from a vertical bar in one eye, and a vertical bar with a gap in the other eye. Observers perceived a transparent square in depth that gave rise to quantitative percepts of depth. The authors argued these displays constituted a new form of stereopsis, since they were “without conventional disparity” and that the depth experienced was due to “transparency rather than occlusion”. Although there were no ...
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Two binocular cues to motion in depth have been identified psychophysically: change of disparity (CD) and interocular velocity difference (IOVD). We evince a third stereomotion cue arising from changes in the extent of binocularly... more
Two binocular cues to motion in depth have been identified psychophysically: change of disparity (CD) and interocular velocity difference (IOVD). We evince a third stereomotion cue arising from changes in the extent of binocularly unpaired regions. In experiment 1, a solid black rectangle was presented to one eye, the other eye viewing two rectangles (each half the width of the larger one), separated by a central vertical gap (unpaired background stereopsis: Gillam et al, 1999 Vision Research 39 493-502). As these rectangles were ...
Motion in depth; MID; Speed perception Psychology Psychology.
Description As we move around the world, complex patterns of visual motion are produced that can in principle be informative about self-motion, or the motion of objects in our visual field. These fields of motion vectors, referred to as... more
Description As we move around the world, complex patterns of visual motion are produced that can in principle be informative about self-motion, or the motion of objects in our visual field. These fields of motion vectors, referred to as optic flow patterns, can be decomposed into four independent first order differential invariants, namely divergence ('div': related to expansion or contraction), curl (related to clockwise or anticlockwise rotation), and 2 components of deformation ('def': dilation and pure shear). Here, experiments are reported ...
Macquarie University ResearchOnline.
Description Variations of perceived speed with spatial frequency (SF), temporal frequency (TF), and contrast have been known for many years. However, these effects have largely been studied in isolation, preventing comparison of the... more
Description Variations of perceived speed with spatial frequency (SF), temporal frequency (TF), and contrast have been known for many years. However, these effects have largely been studied in isolation, preventing comparison of the perceived speed of stimuli across the spatio-temporal frequency surface. We present the first systematic study to establish the perceived speed of high and low contrast (70% and 7%) stimuli across a broad range of Fourier parameters (SFs from 0.25-8c/deg; TFs from 2-16Hz; speeds from 0.25-64deg/s). ...
Macquarie University ResearchOnline.
Description Recent studies have shown that facial images created by‗ morphing 'faces from two different races are generally rated as being more attractive than single-race component faces. It has been suggested that the morphology of... more
Description Recent studies have shown that facial images created by‗ morphing 'faces from two different races are generally rated as being more attractive than single-race component faces. It has been suggested that the morphology of mixed-race faces can be considered a marker for heterozygosity, and hence increased immunocompetence–an attractive trait in mate selection. The current study aimed to examine whether greater racial diversity is associated with greater attractiveness, or whether attractiveness peaks at an optimal level. ...
Description Facial movement may provide cues to identity that can supplement or even supplant static facial information. We investigated whether participants could match dynamic familiar and unfamiliar faces when static cues were... more
Description Facial movement may provide cues to identity that can supplement or even supplant static facial information. We investigated whether participants could match dynamic familiar and unfamiliar faces when static cues were minimised, using facial point-light-displays (PLDs) or shape-averaged avatars. Experiment 1 tested the matching of famous and unfamiliar faces in a same/different task, using the same stimulus type within each pair. Experiment 2 replicated Experiment 1, except that participants attempted to match full-face ...
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In the current study we use contingent face aftereffects to examine the contributions made by morphology and facial luminance cues to the encoding of race. African and European facial images differed in both morphology and luminance (ML),... more
In the current study we use contingent face aftereffects to examine the contributions made by morphology and facial luminance cues to the encoding of race. African and European facial images differed in both morphology and luminance (ML), in morphology alone (M), or in luminance alone (L). Significant aftereffects were found in conditions where test stimuli included morphological information (ML and M), but not when it was absent (L). Furthermore, the size of the aftereffect for test conditions specifying race using both cues (ML) was no greater than when morphological information was the sole cue (M). This suggests that the effects measured here can be accounted for by differences in morphology alone. These results indicate that not only are individual reports of perceived racial typicality more significantly influenced by morphological shape cues than surface cues, but morphological cues appear to form the basis of the underlying neural encoding for faces of different races.
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isual overlay masking is typically studied with a mask and target located at the same depth plane. Masking is reduced when binocular disparity separates the target from the mask (G. Moraglia & B. Schneider, 1990). We replicate this... more
isual overlay masking is typically studied with a mask and target located at the same depth plane. Masking is reduced when binocular disparity separates the target from the mask (G. Moraglia & B. Schneider, 1990). We replicate this finding for a broadband target masked by natural images and find the greatest masking (threshold elevation) when target and mask occupy the same depth plane. Masking was reduced equally whether the target appeared at a crossed or an uncrossed disparity. We measure the tuning of masking and determine the extent of the benefit afforded by disparity. Threshold elevation decreases monotonically with increasing disparity until ±8 arcmin. Two underlying components to the masking are evident; one accounts for around two-thirds of the masking and is independent of disparity. The second component is disparity-dependent and results in additional masking when there is zero disparity. Importantly, the reduction in masking with disparity cannot be explained by interocular decorrelation; we use a single-interval orientation discrimination task to exclude this possibility. We conclude that when the target and mask are presented at different depths they activate distinct populations of disparity-tuned neurons, resulting in less masking of the target.
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Laboratory-based studies of perceived speed show that, under most circumstances, perceived speed is reduced as a function of contrast. However, a recent investigation of perceived vehicular speed while driving around a closed road circuit... more
Laboratory-based studies of perceived speed show that, under most circumstances, perceived speed is reduced as a function of contrast. However, a recent investigation of perceived vehicular speed while driving around a closed road circuit showed no such effect (Owens, Wood, & Carberry, 2010, Perception, 39, 1199–1215). We sought to probe the source of this discrepancy, asking whether the presence or absence of stereoscopic motion information might account for the difference in results. In a two-alternative forced-choice psychophysical speed-discrimination task, observers compared the speed of high- and low-contrast driving clips filmed with a 3‑D camera and presented either stereoscopically (3‑D) or monoscopically (2‑D). Although perceived speed was reduced at low contrast, the size of this misperception was equivalent for 2‑D and 3‑D presentations. However, the inclusion of stereoscopic cues to vehicular speed caused significant improvements in the precision of speed judgments. It is concluded that although stereopsis can provide access to valuable information on perceived speed, contrast-independent speed estimation as demonstrated by Owens et al. (2010) is more likely to reflect the use of the full visual field in a real driving situation (compared with limited field of view simulations), or the additional contributions of nonvisual cues rather than stereopsis.
Research Interests: Perception, Visual perception, Motion perception, Self-Motion Perception, Visual perception (Psychology), and 9 moreHuman Factors in Visual Perception, Perception of Self-Motion, Driving Simulation, Vection, Graphic Driving Simulator, Speed Perception, Driving Simulators, Driving Simulation, and Egomotion
Lightness, or perceived reflectance of a surface, is influenced by surrounding context. This is demonstrated by the Simultaneous Contrast Illusion (SCI), where a gray patch is perceived lighter against a black background and vice versa.... more
Lightness, or perceived reflectance of a surface, is influenced by surrounding context. This is demonstrated by the Simultaneous Contrast Illusion (SCI), where a gray patch is perceived lighter against a black background and vice versa. Conversely, assimilation is where the lightness of the target patch moves toward that of the bounding areas and can be demonstrated in White's effect. Blakeslee and McCourt (1999) introduced an oriented difference-of-Gaussian (ODOG) model that is able to account for both contrast and assimilation in a number of lightness illusions and that has been subsequently improved using localized normalization techniques. We introduce a model inspired by image statistics that is based on a family of exponential filters, with kernels spanning across multiple sizes and shapes. We include an optional second stage of normalization based on contrast gain control. Our model was tested on a well-known set of lightness illusions that have previously been used to evaluate ODOG and its variants, and model lightness values were compared with typical human data. We investigate whether predictive success depends on filters of a particular size or shape and whether pooling information across filters can improve performance. The best single filter correctly predicted the direction of lightness effects for 21 out of 27 illusions. Combining two filters together increased the best performance to 23, with asymptotic performance at 24 for an arbitrarily large combination of filter outputs. While normalization improved prediction magnitudes, it only slightly improved overall scores in direction predictions. The prediction performance of 24 out of 27 illusions equals that of the best performing ODOG variant, with greater parsimony. Our model shows that V1-style orientation-selectivity is not necessary to account for lightness illusions and that a low-level model based on image statistics is able to account for a wide range of both contrast and assimilation effects.
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To improve robustness in object recognition, many artificial visual systems imitate the way in which the human visual cortex encodes object information as a hierarchical set of features. These systems are usually evaluated in terms of... more
To improve robustness in object recognition, many artificial visual systems imitate the way in which the human visual cortex encodes object information as a hierarchical set of features. These systems are usually evaluated in terms of their ability to accurately categorize well-defined, unambiguous objects and scenes. In the real world, however, not all objects and scenes are presented clearly, with well-defined labels and interpretations. Visual illusions demonstrate a disparity between perception and objective reality, allowing psychophysicists to methodically manipulate stimuli and study our interpretation of the environment. One prominent effect, the Müller-Lyer illusion, is demonstrated when the perceived length of a line is contracted (or expanded) by the addition of arrowheads (or arrow-tails) to its ends. HMAX, a benchmark object recognition system, consistently produces a bias when classifying Müller-Lyer images. HMAX is a hierarchical, artificial neural network that imitates the "simple" and "complex" cell layers found in the visual ventral stream. In this study, we perform two experiments to explore the Müller-Lyer illusion in HMAX, asking: (1) How do simple vs. complex cell operations within HMAX affect illusory bias and precision? (2) How does varying the position of the figures in the input image affect classification using HMAX? In our first experiment, we assessed classification after traversing each layer of HMAX and found that in general, kernel operations performed by simple cells increase bias and uncertainty while max-pooling operations executed by complex cells decrease bias and uncertainty. In our second experiment, we increased variation in the positions of figures in the input images that reduced bias and uncertainty in HMAX. Our findings suggest that the Müller-Lyer illusion is exacerbated by the vulnerability of simple cell operations to positional fluctuations, but ameliorated by the robustness of complex cell responses to such variance.
Research Interests: Computer Vision, Visual perception, Computational Neuroscience, Machine Vision, Illusions, and 9 moreOptical Illusions, Muller-Lyer illusion, Pattern Recognition, Computational Neuroscience, Computational Cognitive Neuroscience, Computational neuroscience., Signal and Image Processing, Pattern Recognition, Machine learning, Feature Extraction and Classification of Biomedical signals, Brain Machine Interface (BMI), and Computational Neuroscience, Computational neurosciences, Computational/ Interdisciplinary Neuroscience, and HMAX Model
Facial movement may provide cues to identity, by supporting the extraction of face shape information via structure-from-motion, or via characteristic patterns of movement. Currently, it is unclear whether familiar and unfamiliar faces... more
Facial movement may provide cues to identity, by supporting the extraction of face shape information via structure-from-motion, or via characteristic patterns of movement. Currently, it is unclear whether familiar and unfamiliar faces derive the same benefit from these mechanisms. This study examined the movement advantage by asking participants to match moving and static images of famous and unfamiliar faces to facial point-light displays (PLDs) or shape-normalised avatars in a same/different task (experiment 1). In experiment 2 we also used a same/different task, but participants matched from PLD to PLD or from avatar to avatar. In both experiments, unfamiliar face matching was more accurate for PLDs than for avatars, but there was no effect of stimulus type on famous faces. In experiment 1, there was no movement advantage, but in experiment 2, there was a significant movement advantage for famous and unfamiliar faces. There was no evidence that familiarity increased the movement advantage. For unfamiliar faces, results suggest that participants were relying on characteristic movement patterns to match the faces, and did not derive any extra benefit from the structure-from-motion cues in the PLDs. The results indicate that participants may use static and movement-based cues in a flexible manner when matching famous and unfamiliar faces.
Opposing aftereffects can be simultaneously induced by adapting to faces of different races distorted in opposite directions, allowing researchers to infer that faces are encoded against race-specific prototypes. This effect also suggests... more
Opposing aftereffects can be simultaneously induced by adapting to faces of different races distorted in opposite directions, allowing researchers to infer that faces are encoded against race-specific prototypes. This effect also suggests the existence of dissociable pools of neurons sensitive to race, each of which has been differently adapted to cause an opposite aftereffect. More recent studies have suggested that changes in the strength of race-contingent aftereffects reveal evidence of categorical perception, as they are larger when the adapting faces straddle the racial category boundary. We examined whether changes in these effects more closely correspond to a dichotomous categorical judgment, reflecting highly race-selective neural mechanisms, or more continuous perceptions of racial typicality, reflecting visual channels that are more broadly tuned. In Experiment 1, faces with a range of “morph levels” (i.e., relative contributions of Asian/Caucasian faces) were either rated on a continuous scale for Asian/Caucasian typicality, or simply categorized as Asian/Caucasian. As expected, typicality ratings showed a shallow slope (observers were sensitive to morph level over a broad range), while dichotomous racial categorization showed a steep slope (a rapid switch from categorization as Asian-Caucasian). In Experiment 2, race-contingent adaptation was assessed using test faces with various morph levels. Aftereffect size showed a shallow slope, closely resembling the racial typicality ratings, but showing a significant difference to the categorization data. This suggests that although the visual channels processing these faces do show some selectivity to race, they are sensitive to perceptions of racial typicality, showing a gradual transition of activity across a broad range of faces along the racial continuum.
Research Interests: Perception, Psychophysics of vision, Vision Science, Face Recognition, Visual perception, and 12 moreRace and Ethnicity, Perception and Cognition, Person Perception, Face recognition (Psychology), Perception (Psychology), Face perception, Visual perception (Psychology), Face perception and recognition, Race, Vision, Face processing, and Visual Psychophysics
In two experiments, we demonstrate a misperception of the velocity of a random-dot stimulus moving in the presence of a static line oriented obliquely to the direction of dot motion. As shown in previous studies, the perceived direction... more
In two experiments, we demonstrate a misperception of the velocity of a random-dot stimulus moving in the presence of a static line oriented obliquely to the direction of dot motion. As shown in previous studies, the perceived direction of the dots is shifted away from the orientation of the static line, with the size of the shift varying as a function of line orientation relative to dot direction (the statically-induced direction illusion, or ‘SDI’). In addition, we report a novel effect – that perceived speed also varies as a function of relative line orientation, decreasing systematically as the angle is reduced from 90 to 0. We propose that these illusions both stem from the differential processing of object-relative and non-object-relative component velocities, with the latter being perceptually underestimated with respect to the former by a constant ratio. Although previous proposals regarding the SDI have not allowed quantitative accounts, we present a unified formal model of perceived velocity (both direction and speed) with the magnitude of this ratio as the only free parameter. The model was successful in accounting for the angular repulsion of motion direction across line orientations, and in predicting the systematic decrease in perceived velocity as the line’s angle was reduced. Although fitting for direction and speed produced different best-fit values of the ratio of underestimation of non-object-relative motion compared to object-relative motion (with the ratio for speed being larger than that for direction) this discrepancy may be due to differences in the psychophysical procedures for measuring direction and speed.
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Visual overlay masking is typically studied with a mask and target located at the same depth plane. Masking is reduced when binocular disparity separates the target from the mask (G. Moraglia & B. Schneider, 1990). We replicate this... more
Visual overlay masking is typically studied with a mask and target located at the same depth plane. Masking is reduced when binocular disparity separates the target from the mask (G. Moraglia & B. Schneider, 1990). We replicate this finding for a broadband target masked by natural images and find the greatest masking (threshold elevation) when target and mask occupy the same depth plane. Masking was reduced equally whether the target appeared at a crossed or an uncrossed disparity. We measure the tuning of masking and determine the extent of the benefit afforded by disparity. Threshold elevation decreases monotonically with increasing disparity until +/-8 arcmin. Two underlying components to the masking are evident; one accounts for around two-thirds of the masking and is independent of disparity. The second component is disparity-dependent and results in additional masking when there is zero disparity. Importantly, the reduction in masking with disparity cannot be explained by interocular decorrelation; we use a single-interval orientation discrimination task to exclude this possibility. We conclude that when the target and mask are presented at different depths they activate distinct populations of disparity-tuned neurons, resulting in less masking of the target.
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Faces of individuals with African and European heritage (henceforth referred to as Black and White respectively) feature two major differences: those of skin tone and morphological characteristics. Although considerations of perceived... more
Faces of individuals with African and European heritage (henceforth referred to as Black and White respectively) feature two major differences: those of skin tone and morphological characteristics. Although considerations of perceived race are important to various psychological subdisciplines, to date the relative influence of morphological versus photometric characteristics has not been investigated. We attempted to influence the perceived racial typicality of a central target face by manipulating perceived skin tone using the well-known lightness contrast illusion. As expected, ratings of skin tone were influenced by surround faces, yet ratings of perceived racial typicality were not, suggesting a dissociation between the two judgments. Surprisingly, skin tone contributes little to perceived race, leaving facial morphology as the dominant cue. These results may shed light on failures to find effects of racial typicality in studies of prejudice where judgments were based on photographs with altered skin tone alone.
Research Interests: Perception, Race and Racism, Social Cognition, Visual perception, Race and Ethnicity, and 14 morePrejudice, Intergroup Relations, Stereotypes and Prejudice, Police, Face perception, Visual perception (Psychology), Prejudice (Psychology), Face perception and recognition, Race, Racial Prejudice, Discrimination, Lusotropicalism, Stop and search, Social Status and Aging, Vicarious Police Contact, and Perceptions of Injustice
Studying illusions provides insight into the way the brain processes information. The Müller-Lyer Illusion (MLI) is a classical geometrical illusion of size, in which perceived line length is decreased by arrowheads and increased by... more
Studying illusions provides insight into the way the brain processes information. The Müller-Lyer Illusion (MLI) is a classical geometrical illusion of size, in which perceived line length is decreased by arrowheads and increased by arrowtails. Many theories have been put forward to explain the MLI, such as misapplied size constancy scaling, the statistics of image-source relationships and the filtering properties of signal processing in primary visual areas. Artificial models of the ventral visual processing stream allow us to isolate factors hypothesised to cause the illusion and test how these affect classification performance. We trained a feed-forward feature hierarchical model, HMAX, to perform a dual category line length judgment task (short versus long) with over 90% accuracy. We then tested the system in its ability to judge relative line lengths for images in a control set versus images that induce the MLI in humans. Results from the computational model show an overall illusory effect similar to that experienced by human subjects. No natural images were used for training, implying that misapplied size constancy and image-source statistics are not necessary factors for generating the illusion. A post-hoc analysis of response weights within a representative trained network ruled out the possibility that the illusion is caused by a reliance on information at low spatial frequencies. Our results suggest that the MLI can be produced using only feed-forward, neurophysiological connections.
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This study examined the impact of presentation modality and the effectiveness of direct and indirect measures of deception to distinguish truthful from deceptive confessions. Confession statements were presented in one of three formats:... more
This study examined the impact of presentation modality and the effectiveness of direct and indirect measures of deception to distinguish truthful from deceptive confessions. Confession statements were presented in one of three formats: audiovisual, audioonly, or written text. Forty-six observers classified each statement as true or false and provided ratings of confidence, information sufficiency, perceived cognitive load, and suspiciousness. Compared to audio and written confessions, exposure to audiovisual recordings yielded significantly lower accuracy rates for direct veracity judgements, with below chance level performance. There was no evidence that indirectmeasures assisted observers in discriminating truthful fromdeceptive confessions.Overall, observers showed a strong bias to believe confessions with poor detection rates for false statements. Reliance on video recordings to assess the veracity of confession evidence is unlikely to reduce wrongful convictions arising from false confessions.
The direction illusion is the phenomenal exaggeration of the angle between the drift directions, typically, of two superimposed sets of random dots. The direction illusion is commonly attributed to mutual inhibition between direction... more
The direction illusion is the phenomenal exaggeration of the angle between the drift directions, typically, of two superimposed sets of random dots. The direction illusion is commonly attributed to mutual inhibition between direction selective cell populations (distribution-shift model). A second explanation attributes the direction illusion to the differential processing of relative and non-relative motion components (differential processing model). Our first experiment demonstrates that, as predicted by the differential processing model, a static line can invoke a misperception of direction in a single set of dots – a phenomenon we refer to as the statically-induced direction illusion. In a second experiment, we find that the orientation of a static line can also influence the size of the conventional direction illusion. A third experiment eliminates the possibility that these results can be explained by the presence of motion streaks. While the results of these experiments are in agreement with the predictions made by the differential processing model, they pose serious problems for the distribution-shift account of shifts in perceived
direction.
direction.
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Stereoscopic slant perception around a vertical axis (horizontal slant) is often found to be strongly attenuated relative to geometric prediction. Stereo slant is much greater, however, when an adjacent surface, stereoscopically in the... more
Stereoscopic slant perception around a vertical axis (horizontal slant) is often found to be strongly attenuated relative to geometric prediction. Stereo slant is much greater, however,
when an adjacent surface, stereoscopically in the frontal plane, is added. This slant enhancement is often attributed to the presence of a `reference surface' or to a spatial change in the disparity gradient (introducing second and higher derivatives of disparity). Gillam, Chambers, and Russo (1988 Journal of Experimental Psychology: Human Perception and Performance 14 163-175) questioned the role of these factors in that placement of the frontal-plane surface in a direction collinear with the slant axis (twist configuration) sharply reduced latency for perceiving slant whereas placing the same surface in a direction orthogonal to the slant axis (hinge configuration) had little effect.We here confirm these findings for slant magnitude, showing a striking advantage for twist over hinge configurations.We also examined contrast slant measured on the frontal-plane surface in the hinge and twist configurations. Under conditions where test and inducer surfaces have centres at the same depth for twist and hinge, we found that twist configurations produced strong negative slant contrast, while hinge configurations produced significant positive contrast or slant assimilation.We conclude that stereo slant and contrast effects for neighbouring surfaces can only be understood from the patterns and gradients of step disparities present. It is not adequate to consider the second surface merely as a reference slant for the first or as having its effect via a spatial change in the disparity gradient.
when an adjacent surface, stereoscopically in the frontal plane, is added. This slant enhancement is often attributed to the presence of a `reference surface' or to a spatial change in the disparity gradient (introducing second and higher derivatives of disparity). Gillam, Chambers, and Russo (1988 Journal of Experimental Psychology: Human Perception and Performance 14 163-175) questioned the role of these factors in that placement of the frontal-plane surface in a direction collinear with the slant axis (twist configuration) sharply reduced latency for perceiving slant whereas placing the same surface in a direction orthogonal to the slant axis (hinge configuration) had little effect.We here confirm these findings for slant magnitude, showing a striking advantage for twist over hinge configurations.We also examined contrast slant measured on the frontal-plane surface in the hinge and twist configurations. Under conditions where test and inducer surfaces have centres at the same depth for twist and hinge, we found that twist configurations produced strong negative slant contrast, while hinge configurations produced significant positive contrast or slant assimilation.We conclude that stereo slant and contrast effects for neighbouring surfaces can only be understood from the patterns and gradients of step disparities present. It is not adequate to consider the second surface merely as a reference slant for the first or as having its effect via a spatial change in the disparity gradient.
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Area MT in extrastriate visual cortex is widely believed to be responsible for the perception of object speed. Recent physiological data show that many cells in macaque visual area MT change their speed preferences with a change in... more
Area MT in extrastriate visual cortex is widely believed to be responsible for the perception of object speed. Recent physiological data show that many cells in macaque visual area MT change their speed preferences with a change in stimulus spatial frequency (N. J. Priebe, C. R. Cassanello, & S. G. Lisberger, 2003) and that this effect can accurately predict the dependence of perceived speed on spatial frequency demonstrated in a related psychophysical study (N. J. Priebe & S. G. Lisberger, 2004). For more complex compound gratings and high contrast stimuli, MT cell speed preferences show sharper tuning and less dependence on spatial frequency (Priebe et al., 2003), allowing us to predict that such stimuli should produce speed percepts that are less vulnerable to spatial frequency variations. We investigated the perceived speed of simple sine wave gratings and more complex compound gratings (formed from 2 sine wave components) in response to changes in contrast and spatial frequency. In all cases, high contrast stimuli appeared to translate more rapidly. In addition, high spatial frequencies appeared fasterVthe opposite effect to that predicted by changes in MT cell spatial frequency preferences. Complex grating stimuli were somewhat “protected” from the effect of spatial frequency (compared to simple gratings), as predicted. However, contrary to predictions, the effect of spatial frequency was larger in high (compared to low) contrast gratings. Our data demonstrate that the previously established links between changes in MT cells’ speed preferences and human speed perception are more complex than first thought.
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Previous studies of face recognition and of face matching have shown a general improvement for the processing of internal features as a face becomes more familiar to the participant. In this study, we used a psychophysical two-alternative... more
Previous studies of face recognition and of face matching have shown a general improvement for the processing of internal features as a face becomes more familiar to the participant. In this study, we used a psychophysical two-alternative forced choice paradigm to investigate thresholds for the detection of a displacement of the eyes, nose, mouth, or ears for familiar and unfamiliar faces. No clear division between internal and external features was observed. Rather, for familiar (compared to unfamiliar) faces participants were more sensitive to displacements of internal features such as the eyes or the nose; yet, for our third internal feature--the mouth--no such difference was observed. Despite large displacements, many subjects were unable to perform above chance when stimuli involved shifts in the position of the ears. These results are consistent with the proposal that familiarity effects may be mediated by the construction of a robust representation of a face, although the involvement of attention in the encoding of face stimuli cannot be ruled out. Furthermore, these effects are mediated by information from a spatial configuration of features, rather than by purely feature-based information.
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Abstract The role of two binocular cues to motion in depth—changing disparity (CD) and interocular velocity difference (IOVD)—was investigated by measuring stereomotion speed discrimination and static disparity discrimination performance... more
Abstract The role of two binocular cues to motion in depth—changing disparity (CD) and interocular velocity difference (IOVD)—was investigated by measuring stereomotion speed discrimination and static disparity discrimination performance (stereoacuity). Speed discrimination thresholds were assessed both for random dot stereograms (RDS), and for their temporally uncorrelated equivalents, dynamic random dot stereograms (DRDS), at relative disparity pedestals of− 19, 0, and+ 19 arcmin.
Motion perception involves the processing of velocity signals through several hierarchical stages of the visual cortex. To better understand this process, a number of studies have sought to localize the neural substrates of two... more
Motion perception involves the processing of velocity signals through several hierarchical stages of the visual cortex. To better understand this process, a number of studies have sought to localize the neural substrates of two misperceptions of motion direction, the direction illusion (DI) and the direction aftereffect (DAE). These studies have produced contradictory evidence as to the hierarchical order of the processing stages from which the respective phenomena arise. We have used a simple stimulus configuration to further investigate the sequential order of processes giving rise to the DI and DAE. To this end, we measured the two phenomena invoked in combination, and also manually parsed this combined effect into its two constituents by measuring the two phenomena individually in both possible sequential orders. Comparing the outcomes from each order to the outcome from the combined effect allowed us to test the tenability of two models: the DAE-first model and the DI-first model. Our results indicate that DAE-invoking activity does not occur earlier in the motion processing hierarchy than DI-invoking activity. Although the DI-first model is not inconsistent with our data, the possible involvement of non-sequential processing may be better able to reconcile these results with those of previous studies.
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It has been established that the motion in depth of stimuli visible to both eyes may be signalled binocularly either by a change of disparity over time or by the difference in the velocity of the images projected on each retina, known as... more
It has been established that the motion in depth of stimuli visible to both eyes may be signalled binocularly either by a change of disparity over time or by the difference in the velocity of the images projected on each retina, known as an interocular velocity difference. A two-interval forced-choice stereomotion speed discrimination experiment was performed on four participants to ascertain the relative speed of a persistent random dot stereogram (RDS) and a dynamic RDS undergoing directly approaching or receding motion in depth. While the persistent RDS pattern involved identical dot patterns translating in opposite directions in each eye, and hence included both changing disparity and interocular velocity difference cues, the dynamic RDS pattern (which contains no coherent monocular motion signals) specified motion in depth through changing disparity, but no motion through interocular velocity difference. Despite an interocular velocity difference speed signal of zero motion in depth, the dynamic RDS stimulus appeared to move more rapidly. These observations are consistent with a scheme in which cues that rely on coherent monocular motion signals (such as looming and the interocular velocity difference cue) are less influential in dynamic stimuli due to their lack of reliability (i.e., increased noise). While dynamic RDS stimuli may be relatively unaffected by the contributions of such cues when they signal that the stimulus did not move in depth, the persistent RDS stimulus may retain a significant and conflicting contribution from the looming cue, resulting in a lower perceived speed.
The perceived speed of motion in depth (MID) for a monocularly visible target was measured in central and peripheral vision using a 2AFC speed discrimination task. Only binocular cues to MID were available: changing disparity and... more
The perceived speed of motion in depth (MID) for a monocularly visible target was measured in central and peripheral vision using a 2AFC speed discrimination task. Only binocular cues to MID were available: changing disparity and interocular velocity difference (IOVD). Perceived speed for monocular lateral motion and perceived depth for static disparity were also assessed, again in both central and peripheral vision. The purpose of the experiment was to assess the relative contributions of changing disparity and IOVD cues to the perceived speed of stereomotion. Although peripheral stimuli appeared to lie at approximately the same depth as their central counterparts, their apparent speed was reduced. Monocular/lateral and binocular/MID speeds were reduced to a similar extent. It seems that reduced apparent monocular speed leads to reduced perceived MID speed, despite the fact that the disparity system appears to be unaffected. These results suggest that the IOVD cue makes a significant contribution to MID speed perception.
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Perceived stereomotion trajectory was measured before and after adaptation to lateral motion in the dominant or nondominant eye to assess the relative contributions of 2 cues: changing disparity and interocular velocity difference.... more
Perceived stereomotion trajectory was measured before and after adaptation to lateral motion in the dominant or nondominant eye to assess the relative contributions of 2 cues: changing disparity and interocular velocity difference. Perceived speed for monocular lateral motion and perceived binocular visual direction (BVD) was also assessed. Unlike stereomotion trajectory perception, the BVD of static targets showed an ocular dominance bias, even without adaptation. Adaptation caused equivalent biases in perceived trajectory and monocular motion speed, without significantly affecting perceived BVD. Predictions from monocular motion data closely match trajectory perception data, unlike those from BVD sources. The results suggest that the interocular velocity differences make a significant contribution to stereomotion trajectory perception.
Research Interests:
It has long been known that ocular pursuit of a moving target has a major influence on its perceived speed (Aubert, 1886; Fleischl, 1882). However, little is known about the effect of smooth pursuit on the perception of target direction.... more
It has long been known that ocular pursuit of a moving target has a major influence on its perceived speed (Aubert, 1886; Fleischl, 1882). However, little is known about the effect of smooth pursuit on the perception of target direction. Here we compare the precision of human visual-direction judgments under two oculomotor conditions (pursuit vs. fixation). We also examine the impact of stimulus duration (200 ms vs. ~800 ms) and absolute direction (cardinal vs. oblique). Our main finding is that direction discrimination thresholds in the fixation and pursuit conditions are indistinguishable. Furthermore, the two oculomotor conditions showed oblique effects of similar magnitudes. These data suggest that the neural direction signals supporting perception are the same with or without pursuit, despite remarkably different retinal stimulation. During fixation, the stimulus information is restricted to large, purely peripheral retinal motion, while during steady-state pursuit, the stimulus information consists of small, unreliable foveal retinal motion and a large efference-copy signal. A parsimonious explanation of our findings is that the signal limiting the precision of direction judgments is a neural estimate of target motion in head-centered (or world-centered) coordinates (i.e., a combined retinal and eye motion signal) as found in the medial superior temporal area (MST), and not simply an estimate of retinal motion as found in the middle temporal area (MT).
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Howard and Duke [Howard, I.P., & Duke, P.A. (2003). Monocular transparency generates quantitative depth. Vision Research, 43, 2615–2621] recently proposed a new source of binocular information they claim is used to recover depth in... more
Howard and Duke [Howard, I.P., & Duke, P.A. (2003). Monocular transparency generates quantitative depth. Vision Research, 43, 2615–2621] recently proposed a new source of binocular information they claim is used to recover depth in stereoscopic displays. They argued that these displays lack conventional disparity and that the metrical depth experienced results from transparency rather than occlusion relations. Using a variety of modified versions of their stimuli, we show here that the conditions for transparency are not required to elicit the depth experienced in their stereograms. We demonstrated that quantitative and precise depth depended not on the presence of transparency but on the presence of horizontal contours of the same contrast polarity. Depth was attenuated, particularly at larger target offsets, when horizontal contours had opposite contrast polarity for at least a portion of their length. We also show that a demonstration Howard and Duke used to control for the role of horizontal contours can be understood as an example of Gillam et al.’s Gillam, B.J., Blackburn, S., & Nakayama, K. (1999). Stereopsis based on monocular gaps: metrical coding of depth and slant without matching contours. Vision Research, 39, 493–502 monocular gap stereopsis; a form of binocular occlusion. In summary the findings reported by Howard and Duke can be understood by known processes for the computation of binocular disparity and binocular occlusion.
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We present a novel binocular stimulus without conventional disparity cues whose presence and depth are revealed by sequential monocular stimulation (delay P 80 ms). Vertical white lines were occluded as they passed behind an otherwise... more
We present a novel binocular stimulus without conventional disparity cues whose presence and depth are revealed by sequential monocular stimulation (delay P 80 ms). Vertical white lines were occluded as they passed behind an otherwise camouflaged black rectangular target. The location (and instant) of the occlusion event, decamouflaging the targets edges, differed in the two eyes. Probe settings to match the depth of the black rectangular target showed a monotonic increase with simulated depth. Control tests discounted the possibility of subjects integrating retinal disparities over an extended temporal window or using temporal disparity. Sequential monocular decamouflage was found to be as precise and accurate as conventional simultaneous stereopsis with equivalent depths and exposure durations.
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Until recently, it was considered necessary for features in the two eyes to be matched before the evaluation of differences in their locations (binocular disparities) could reveal depth information. Motion in depth can also be perceived... more
Until recently, it was considered necessary for features in the two eyes to be matched before the evaluation of differences in their locations (binocular disparities) could reveal depth information. Motion in depth can also be perceived binocularly from related changes in the locations of matched binocular features. However, unmatched features can arise when a binocular object occludes more distant features in one eye but not the other. The presence and extent of such features can provide quantitative depth information, although perceived depth relative to geometrical predictions may vary from one such arrangement to another. The ability of humans to perceive motion in depth from unmatched stimuli has not previously been explored. Here, we use B. Gillam, S. Blackburn, and K. Nakayama’s (1999) ‘‘monocular gap’’ stimuli to investigate perception of motion in depth simulated by a change in the extent of a monocularly occluded feature in a binocular display. Settings of a motion in depth probe revealed that the magnitude of perceived motion in depth is generally as large as that for a stimulus containing matchable binocular features. We show that our stimuli provide disambiguating information not present in similar static stimuli. We conclude that in the computation of motion in depth, a binocular match is not required. A new cue--dynamic half-occlusion--can be used to reach an accurate percept.
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To examine the spatial scale of the mechanisms supporting the perception of motion in depth defined by binocular cues, we measured stereomotion speed discrimination thresholds as a function of stimulus size using a two-interval speed... more
To examine the spatial scale of the mechanisms supporting the perception of motion in depth defined by binocular cues, we measured stereomotion speed discrimination thresholds as a function of stimulus size using a two-interval speed comparison task. Stimuli were either random dot stereogram (RDS) bars featuring both the changing disparity (CD) and the interocular velocity difference (IOVD) cues to motion in depth or dynamic random dot stereogram (DRDS) bars featuring the CD cue alone. Monocular speed discrimination performance was also assessed, using half-images of the RDS stimulus. In addition, subjects’ stereoacuity for stationary versions of the binocular stimuli was measured. Stimuli ranged in vertical extent from 1.25 to 40 min. Sensitivity to speed differences was strongly related to stimulus height for DRDS stimuli. Performance decreased rapidly as stimulus size was reduced, becoming nearly random for heights below 5 min. However, for RDS stimuli, speed discrimination performance declined with reductions in stimulus size at a far slower rate, providing superior performance at every stimulus size used. Monocular performance was superior still for the majority of subjects, yet showed a similar rate of decline to binocular RDS stimuli. We conclude that the spatial resolution of the CD mechanism and its static disparity inputs is, on average, nearly nine times more coarse than the IOVD system and its monocular motion inputs. Static stereoacuity controls show that this finding cannot be explained by differences in the disparity signals available in our RDS and DRDS stimuli.
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Under usual circumstances, motion in depth is associated with conventional stereomotion cues: a change in disparity and differences between object velocities in each monocular image. However, occasionally these cues are unavailable due to... more
Under usual circumstances, motion in depth is associated with conventional stereomotion cues: a change in disparity and differences between object velocities in each monocular image. However, occasionally these cues are unavailable due to the fact that in one eye the object may be occluded by, or camouflaged against appropriately positioned binocular objects. We report two experiments concerned with stereomotion perception under conditions of monocular camouflage. In Experiment 1, the visible half-image of a monocularly camouflaged object translated laterally. In this binocular context, percepts of lateral motion and motion in depth were equally consistent with the stimulus. Subjects perceived an oblique trajectory of 3D motion, compared to the more direct 3D trajectory experienced for binocularly matched stimuli. In Experiment 2, the perceived velocity of stereomotion was assessed. Again, for the stimulus used in Experiment 1, perceived stereomotion speed was lower than that for matched stimuli. However, when additional background objects were present, tightening the ecological constraints, perceived stereomotion velocity was often equivalent to that for matched stimuli. These results demonstrate for the first time that the motion of a monocularly camouflaged object can result in the perception of stereomotion, and that the perceived trajectory and speed are influenced by the ecological constraints of binocular geometry.
Research Interests:
Previous studies have shown that people's ability to detect, from memory, alterations in highly familiar faces is excellent. Indeed, just noticeable differences for the detection of small alterations in a recognition-memory task were not... more
Previous studies have shown that people's ability to detect, from memory, alterations in highly familiar faces is excellent. Indeed, just noticeable differences for the detection of small alterations in a recognition-memory task were not significantly different from the corresponding measures in a perceptual-discrimination task (Bre¨dart and Devue, 2006 Perception 35 101-106; Ge et al, 2003 Perception 32 601-614). The object of the present study was to evaluate whether people's perceptual memory for body shapes of very familiar persons reaches the high level of precision that was reported for face memory. For one group of participants, the task was to detect body shape alterations (an increase or a decrease of 2% to 10% of the waist-to-hip ratio) on photographs depicting either themselves or a friend. For another group of participants who did not know the target persons, the task was to discriminate whether two photographs presented side by side were the same or not. Results showed that the detection of alterations was significantly
better in the perceptual-discrimination task than in the recognition-memory tasks (for the participant's own body as well as for the friend's body). In conclusion, the high fidelity of perceptual memory for very familiar faces does not extend to familiar body shapes.
better in the perceptual-discrimination task than in the recognition-memory tasks (for the participant's own body as well as for the friend's body). In conclusion, the high fidelity of perceptual memory for very familiar faces does not extend to familiar body shapes.
Research Interests:
Familiarity plays an important role in face processing. The importance of familiarity is increased when facial form cues are degraded, so that a person must rely primarily on movement (dynamic) information to identify someone. It is,... more
Familiarity plays an important role in face processing. The importance of familiarity is increased when facial form cues are degraded, so that a person must rely primarily on movement (dynamic) information to identify someone. It is, however, unclear which dynamic cues are used for face recognition of both familiar and unfamiliar faces. Furthermore, little work has been done on dynamic self-face recognition, and none has focused on the type of movement that facilitates this process. The current study used motion capture cameras to record and isolate facial movements in order to test recognition of self, familiar and unfamiliar faces. Participants completed a 2AFC same/different face-matching task involving point-light displays of natural motion (i.e. both rigid and non-rigid motion), rigid motion only (e.g. nodding/shaking), non-rigid motion only (e.g. mouth/eyebrow motion) and still images to determine whether differences in familiarity resulted in the use of different movement cues. The manner (style) in which someone is speaking may also impact on whether they can be easily identified from dynamic cues. Consequently, speech style was either matched or mismatched between video clips. We found that matching performance was more accurate overall when speech style was matched than mismatched. Familiar face matching appears to use rigid, non-rigid and natural movement cues equally, but unfamiliar and self-face matching are more accurate for rigid than natural motion when speech style differs between clips. These results are discussed in relation to previous research on dynamic face recognition, and possible
implications for current face processing models.
implications for current face processing models.
Research Interests:
The aim of the current experiment was to explore the possibility that people’s perceptions of race could be altered using lightness contrast effects. To test this, faces ranging from typically Caucasian (white) to typically African... more
The aim of the current experiment was to explore the possibility that people’s perceptions of race could be altered using lightness contrast effects. To test this, faces ranging from typically Caucasian (white) to typically African (black) were surrounded with either black or white faces. Participants were asked to rate how stereotypically white or black they perceived the central face image to be. A 2x5 repeated measures ANOVA revealed that participants rated faces as looking the same whether presented in white or black surrounds. A second experiment consisting of two parts was conducted in an attempt to explain this lack of an effect. In experiment 2a, the effect of skin tone luminance variations without differences in facial morphology were investigated, while experiment 2b studied the effects of morphology without differences in skin tone. While skin tone alone yielded an effect of perceived lightness, the perceived race of faces was not affected by the morphologically different surrounds. This suggests that although perceptions of skin tone can be altered using lightness contrast effects, this is not sufficient to alter overall racial appearance, questioning the role of skin tone in the perception of race.
Research Interests:
Enhanced visual search is widely reported in autism. Here we note a similar advantage for university students self-reporting higher levels of autism-like traits. Contrary to prevailing theories of autism, performance was not associated... more
Enhanced visual search is widely reported in autism. Here we note a similar advantage for university students self-reporting higher levels of autism-like traits. Contrary to prevailing theories of autism, performance was not associated with perceptual-discrimination thresholds for the same stimuli, but was associated with inspection-time threshold--a measure of speed of perceptual processing. Enhanced visual search in autism may, therefore, at least partially be explained by faster speed of processing.
Research Interests:
The precision and accuracy of speed discrimination performance for stereomotion stimuli were assessed for several receding 3D trajectories confined to the horizontal meridian. It has previously been demonstrated in a variety of tasks that... more
The precision and accuracy of speed discrimination performance for stereomotion stimuli were assessed for several receding 3D trajectories confined to the horizontal meridian. It has previously been demonstrated in a variety of tasks that detection thresholds are substantially higher when subjects observe a stereomotion stimulus than when simply viewing one of its component monocular half-imagesVa phenomenon known as stereomotion suppression (C. W. Tyler, 1971). Using monocularly visible motion in depth targets, we found mean speed discrimination thresholds to be higher for stereomotion,
compared with monocular lateral speed discrimination thresholds for equivalent stimuli, demonstrating a disadvantage for binocular viewing in the case of speed discrimination as well. Furthermore, speed discrimination thresholds for motion in depth were not systematically affected by trajectory angle; hence, the disadvantage of binocular viewing persists even when there are concurrent changes in binocular visual direction. Lastly, there was a tendency for oblique trajectories of stereomotion to be perceived as faster than equally rapid motion receding directly away from the subject along the midline. Our data, in addition to earlier stereomotion suppression observations, are consistent with a stereomotion system that takes a noisy, weighted difference of the stimulus velocities in the two eyes to compute motion in depth.
compared with monocular lateral speed discrimination thresholds for equivalent stimuli, demonstrating a disadvantage for binocular viewing in the case of speed discrimination as well. Furthermore, speed discrimination thresholds for motion in depth were not systematically affected by trajectory angle; hence, the disadvantage of binocular viewing persists even when there are concurrent changes in binocular visual direction. Lastly, there was a tendency for oblique trajectories of stereomotion to be perceived as faster than equally rapid motion receding directly away from the subject along the midline. Our data, in addition to earlier stereomotion suppression observations, are consistent with a stereomotion system that takes a noisy, weighted difference of the stimulus velocities in the two eyes to compute motion in depth.
Research Interests: Psychophysics, Perception, Psychophysics of vision, Visual perception, Binocular vision, and 11 moreMotion perception, Stereopsis, Stereo Vision (Computer Vision), Self-Motion Perception, Visual perception (Psychology), Human Factors in Visual Perception, Perception of Self-Motion, 3D display & stereopsis, Psychology of Visual Perception, Motion in depth, and Stereomotion
The effect of contrast on the perception of stimulus speed for stereomotion and monocular lateral motion was investigated for successive matches in random-dot stimuli. The familiar `Thompson effect' - that a reduction in contrast leads to... more
The effect of contrast on the perception of stimulus speed for stereomotion and monocular lateral motion was investigated for successive matches in random-dot stimuli. The familiar `Thompson effect' - that a reduction in contrast leads to a reduction in perceived speed - was found in similar proportions for both binocular images moving in depth, and for monocular images translating laterally. This result is consistent with the idea that the monocular motion system has a significant input to the stereomotion system, and dominates the speed percept for approaching motion.
Research Interests: Psychophysics, Perception, Psychophysics of vision, Visual perception, Binocular vision, and 11 moreMotion perception, Stereopsis, Stereo Vision (Computer Vision), Self-Motion Perception, Visual perception (Psychology), Human Factors in Visual Perception, Perception of Self-Motion, 3D display & stereopsis, Psychology of Visual Perception, Motion in depth, and Stereomotion
Two experiments are presented assessing the contributions of the rate of change of disparity (CD) and interocular velocity difference (IOVD) cues to stereomotion speed perception. Using a two-interval forced-choice paradigm, the perceived... more
Two experiments are presented assessing the contributions of the rate of change of disparity (CD) and interocular velocity difference (IOVD) cues to stereomotion speed perception. Using a two-interval forced-choice paradigm, the perceived speed of directly approaching and receding stereomotion and of monocular lateral motion in random dot stereogram (RDS) targets was measured. Prior adaptation using dysjunctively moving random dot stimuli induced a velocity aftereffect (VAE). The degree of interocular correlation in the adapting images was manipulated to assess the effectiveness of each cue. While correlated adaptation involved a conventional RDS stimulus, containing both IOVD and CD cues, uncorrelated adaptation featured an independent dot array in each monocular half-image, and hence lacked a coherent disparity signal. Adaptation produced a larger VAE for stereomotion than for monocular lateral motion, implying effects at neural sites beyond that of binocular combination. For motion passing through the horopter, correlated and uncorrelated adaptation stimuli produced equivalent stereomotion VAEs. The possibility that these results were due to the adaptation of a CD mechanism through random matches in the uncorrelated stimulus was discounted in a control experiment. Here both simultaneous and sequential adaptation of left and right eyes produced similar stereomotion VAEs. Motion at uncrossed disparities was also affected by both correlated and uncorrelated adaptation stimuli, but showed a significantly greater VAE in response to the former. These results show that (1) there are two separate, specialised mechanisms for encoding stereomotion: one through IOVD, the other through CD; (2) the IOVD cue dominates the perception of stereomotion speed for stimuli passing through the horopter; and (3) at a disparity pedestal both the IOVD and the CD cues have a significant influence.
Research Interests: Psychophysics, Perception, Psychophysics of vision, Visual perception, Binocular vision, and 12 moreMotion perception, Stereopsis, Stereo Vision (Computer Vision), Self-Motion Perception, Visual perception (Psychology), Human Factors in Visual Perception, Perception of Self-Motion, 3D display & stereopsis, Psychology of Visual Perception, Motion in depth, Stereomotion, and Motion Aftereffect
It is well-known that reducing the contrast of a slow moving stimulus reduces its apparent speed. [Thompson, P. (1982). Perceived rate of movement depends on contrast. Vision Research, 22, 377–380.] report of this finding also suggested... more
It is well-known that reducing the contrast of a slow moving stimulus reduces its apparent speed. [Thompson, P. (1982). Perceived rate of movement depends on contrast. Vision Research, 22, 377–380.] report of this finding also suggested that at speeds above 8 cycles/s reducing contrast increased perceived speed. However in a later report, Stone and Thompson (1992), using a more rigorous, forced-choice procedure, failed to collect reliable data at these higher speeds. Here, we confirm that faster moving stimuli can appear to move faster than their true speed at low contrasts and we propose a physiologically plausible ratio model that unlike recent Bayesian models (e.g. Weiss, Y., Simoncelli, E. P., & Adelson, E. H. (2002). Motion illusions as optimal percepts. Nature Neuroscience, 5, 598–604) can account well for the results.