John Cass

Western Sydney University, Psychology, Faculty Member

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Senior Lecturer in Psychophysics and Sensory Neuroscience

Undergraduate Honours degree:
University of Wollongong.

PhD:
University of New South Wales.

Post-docs:
School of Physiology, University of Sydney (David Alais)
School of Psychology, University of New South Wales (Branka Spehar & Bart Anderson)
Institute of Ophthalmology, University College London (Steven Dakin & Peter Bex)

Australian Post-Doctoral Research Fellow:
School of Psychology, University of Sydney

Appointed to Research Lecturer in School of Psychology, University of Western Sydney - beginning 2010.

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Papers by John Cass

Effects of stress on perceptual learning in a virtual reality environment

by John Cass and G. Weidemann

Frontiers in Virtual Reality, 2025

Introduction: This study investigates two key questions in perceptual learning using a ten-day vi... more Introduction: This study investigates two key questions in perceptual learning using a ten-day visual training protocol embedded in a first-person shooter (FPS) task within virtual reality (VR): (1) whether training improves the visual system's ability to integrate orientation information across the visual field, and (2) whether aversive electrodermal stimulation and associated stress levels influence perceptual performance and/or learning. Method: 17 participants successfully completed an orientation-averaging task involving Gabor arrays of varying set-sizes (1, 2, 4, or 8 elements) under three shock conditions: no shock, performance-contingent shock, and random shock. Results: Training led to improvements in both accuracy and response times, while increasing set-size monotonically impaired performance. The interaction between training and set-size was weak, suggesting that training benefits likely emerge at a post-integration or decisional stage. Stress responses, indexed by the State-Trait Anxiety Inventory (STAI), confirmed elevated anxiety in both shock conditions compared to control. However, this increase in state anxiety did not reliably affect task performance or learning outcomes, nor did it modulate setsize effects. Notably, participants' accuracy degraded when an on-screen health bar depicted lower "health" levels, regardless of actual shock delivery or contingency. Discussion: These findings indicate that visual feedback cues can shape engagement or motivation independently of experienced stress. More broadly, the results underscore the role of motivational and attentional mechanisms in immersive training environments and provide a framework for evaluating stress effects using subjective anxiety and objective psychophysical measures.

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Reciprocal roles of crowding and serial dependence on visual perception

bioRxiv, 2025

Visual perception arises from the interplay between current and prior sensory inputs. Two percept... more Visual perception arises from the interplay between current and prior sensory inputs. Two perceptual phenomena; serial dependence and visual crowding; result from the mandatory integration of retinal information across time and space, respectively. This study investigated, for the first time, their functional relationship for orientation and brightness discrimination tasks. Participants performed orientation and brightness discrimination tasks (blocked) on peripheral targets surrounded by distractors of varying color, orientation, and proximity. Both serial dependence (the influence of prior stimuli on current judgments) and visual crowding (impaired peripheral recognition caused by nearby distractors) were observed. Similar double dissociations in task and stimulus specificity emerged for both phenomena, suggesting functional links mediated by distinct processing mechanisms for brightness and orientation judgments. Additionally, the two effects interacted: crowding reduced serial dependence on subsequent trials, indicating that spatial information is prioritized over temporal information when spatial redundancy is high. Conversely, serial dependence increased crowding for orientation judgments, while for brightness judgments, serial dependence operated additively without affecting crowding. These interactions were spatially specific, occurring only when targets appeared in the same location across consecutive trials. Notably, a positive correlation between crowding and serial dependence was found exclusively for orientation judgments and only when targets appeared at the same location across trials. The reciprocal interaction and positive correlation between serial dependence and crowding observed for orientation judgments indicate that that these processes are intrinsically linked, possibly via a common neural mechanism. In contrast, for brightness judgments, the unilateral effect of crowding on serial dependence, along with the absence of correlation, indicates distinct neural mechanisms. Here, brightness crowding likely precedes serial dependence, reflecting a prioritization of spatial redundancy minimization over temporal stabilization. These findings suggest that the brain strategically integrates spatial and temporal information through distinct yet overlapping mechanisms, balancing spatial precision with temporal stability based on task demands and stimulus characteristics.

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Development and validation of the New Somatomorphic Matrix–Male: A figural rating scale for measuring male actual–ideal body discrepancy

Psychology of Men & Masculinities, 2018

This study aimed to develop and examine the validity evidence of the New Somatomorphic Matrix–Mal... more This study aimed to develop and examine the validity evidence of the New Somatomorphic Matrix–Male (NSM-M) as a measure of actual–ideal body discrepancy. The NSM-M is a visual matrix of 34 male bodies that vary along two dimensions: body fat percentage (range = 4–40%) and muscularity (fat-free mass index; range = 16.5–30 kg/m2; 36.4–66.1 lbs/m2). In Study 1, participants were 2,733 sexual minority males recruited via a geosocial networking smartphone application. Participants selected their “actual” and “ideal” bodies on the NSM-M and additionally completed questionnaires measuring body dissatisfaction, eating disorder symptoms, quality of life, and anabolic steroid use. In Study 2, participants were 33 males from a community sample. They completed the NSM-M across two sessions, 7–14 days apart. NSM-M scores demonstrated concurrent and convergent validity as a measure of male body dissatisfaction. In addition, NSM-M scores discriminated between steroid users and nonusers, and between body mass index categories. The NSM-M also demonstrated sound test–retest reliability across a 7- to 14-day period. In sum, the NSM-M is validated figural measure of male actual–ideal body discrepancy with notable strengths, including fast administration time and enhanced ecological validity. (PsycINFO Database Record (c) 2018 APA, all rights reserved

A CODE model bridging crowding in sparse and dense displays

Vision Research, Jan 31, 2024

Visual crowding is arguably the strongest limitation imposed on extrafoveal vision, and is a rela... more Visual crowding is arguably the strongest limitation imposed on extrafoveal vision, and is a relatively wellunderstood phenomenon. However, most investigations and theories are based on sparse displays consisting of a target and at most a handful of flanker objects. Recent findings suggest that the laws thought to govern crowding may not hold for densely cluttered displays, and that grouping and nearest neighbour effects may be more important. Here we present a computational model that accounts for crowding effects in both sparse and dense displays. The model is an adaptation and extension of an earlier model that has previously successfully accounted for spatial clustering, numerosity and object-based attention phenomena. Our model combines grouping by proximity and similarity with a nearest neighbour rule, and defines crowding as the extent to which target and flankers fail to segment. We show that when the model is optimized for explaining crowding phenomena in classic, sparse displays, it also does a good job in capturing novel crowding patterns in dense displays, in both existing and new data sets. The model thus ties together different principles governing crowding, specifically Bouma&#39;s law, grouping, and nearest neighbour similarity effects.

Low or high frequency flicker captures attention

Rapid recalibration to audiovisual asynchrony follows the physical—not the perceived—temporal order

Attention, perception & psychophysics, Jul 2, 2018

In natural scenes, audiovisual events deriving from the same source are synchronized at their ori... more In natural scenes, audiovisual events deriving from the same source are synchronized at their origin. However, from the perspective of the observer, there are likely to be significant multisensory delays due to physical and neural latencies. Fortunately, our brain appears to compensate for the resulting latency differences by rapidly adapting to asynchronous audiovisual events by shifting the point of subjective synchrony (PSS) in the direction of the leading modality of the most recent event. Here we examined whether it is the perceived modality order of this prior lag or its physical order that determines the direction of the subsequent rapid recalibration. On each experimental trial, a brief tone pip and flash were presented across a range of stimulus onset asynchronies (SOAs). The participants' task alternated over trials: On adaptor trials, audition either led or lagged vision with fixed SOAs, and participants judged the order of the audiovisual event; on test trials, the SOA as well as the modality order varied randomly, and participants judged whether or not the event was synchronized. For test trials, we showed that the PSS shifted in the direction of the physical rather than the perceived (reported) modality order of the preceding adaptor trial. These results suggest that rapid temporal recalibration is determined by the physical timing of the preceding events, not by one's prior perceptual decisions.

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A CODE model bridging crowding in sparse and dense displays

Vision Research, 2024

Visual crowding is arguably the strongest limitation imposed on extrafoveal vision, and is a rela... more Visual crowding is arguably the strongest limitation imposed on extrafoveal vision, and is a relatively wellunderstood phenomenon. However, most investigations and theories are based on sparse displays consisting of a target and at most a handful of flanker objects. Recent findings suggest that the laws thought to govern crowding may not hold for densely cluttered displays, and that grouping and nearest neighbour effects may be more important. Here we present a computational model that accounts for crowding effects in both sparse and dense displays. The model is an adaptation and extension of an earlier model that has previously successfully accounted for spatial clustering, numerosity and object-based attention phenomena. Our model combines grouping by proximity and similarity with a nearest neighbour rule, and defines crowding as the extent to which target and flankers fail to segment. We show that when the model is optimized for explaining crowding phenomena in classic, sparse displays, it also does a good job in capturing novel crowding patterns in dense displays, in both existing and new data sets. The model thus ties together different principles governing crowding, specifically Bouma's law, grouping, and nearest neighbour similarity effects.

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Efficient Visual Search from Synchronized Auditory Signals Requires Transient Audiovisual Events

PLOS ONE, May 14, 2010

Background: A prevailing view is that audiovisual integration requires temporally coincident sign... more Background: A prevailing view is that audiovisual integration requires temporally coincident signals. However, a recent study failed to find any evidence for audiovisual integration in visual search even when using synchronized audiovisual events. An important question is what information is critical to observe audiovisual integration. Methodology/Principal Findings: Here we demonstrate that temporal coincidence (i.e., synchrony) of auditory and visual components can trigger audiovisual interaction in cluttered displays and consequently produce very fast and efficient target identification. In visual search experiments, subjects found a modulating visual target vastly more efficiently when it was paired with a synchronous auditory signal. By manipulating the kind of temporal modulation (sine wave vs. square wave vs. difference wave; harmonic sine-wave synthesis; gradient of onset/offset ramps) we show that abrupt visual events are required for this search efficiency to occur, and that sinusoidal audiovisual modulations do not support efficient search. Conclusions/Significance: Thus, audiovisual temporal alignment will only lead to benefits in visual search if the changes in the component signals are both synchronized and transient. We propose that transient signals are necessary in synchronydriven binding to avoid spurious interactions with unrelated signals when these occur close together in time.

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Visual crowding: Double dissociation between orientation and brightness judgments

Journal of Vision, 2023

Peripherally presented objects are often more difficult to identify when located in cluttered vis... more Peripherally presented objects are often more difficult to identify when located in cluttered visual environments than when presented in isolation, a phenomenon known as visual crowding. Crowding tends to be stronger when target and nearby flanking elements are composed of similar sets of features. This study investigates the extent to which target-flanker orientation and/or color similarity determines luminance and orientation performance across different tasks under identical stimulus conditions. Targets were near-vertical Gabor patches defined by modulating only the green component of the RGB display. Subjects performed both target luminance and orientation discrimination tasks in separate blocks while both flanker hue (green or red flankers) and orientation (vertical or horizontal flankers) were manipulated as a function of target-flanker separation. We find strong evidence for a double dissociation between task and the specific set of features by which target-flanker similarity is defined. Whereas luminance judgments were highly contingent upon target-flanker hue similarity, orientation judgments showed the inverse pattern, largely contingent upon flanker orientation. The magnitude of this double dissociation decreased with target-flanker separation, at a rate predicted by Bouma's law. This specific pattern of performance provides strong support for the idea that crowding operates independently for the most part within orientation and color domains. That luminance judgments are constrained by target-flanker flanker hue similarity and, to a far lesser extent, by target-flanker orientation similarity suggests that the neural mechanisms responsible for mediating perceived luminance are principally linked to those mediating stimulus hue independent of those mediating stimulus orientation.

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Dichoptic suppression of flanking stimuli breaks crowding

Perception, 2011

Visual crowding refers to the profound impairment in target identification when a peripheral targ... more Visual crowding refers to the profound impairment in target identification when a peripheral target is presented in the context of nearby flanking elements. It is particularly strong at low spatial frequencies. We sought to determine whether the deleterious effects of crowding may be reduced by dichoptically suppressing flanking stimuli from awareness. Target and flanking stimuli were narrowband-filtered Sloan letters whose spatial frequency (SF) content was independently manipulated, peaking at 1.8 or 7.4 cpd. Using LCD shutter glasses, the ...

Dynamic distractor environments reveal classic visual field anisotropies for judgments of temporal order

Attention, Perception, & Psychophysics, 2018

Numerous studies have shown that visual performance critically depends on the stimulus' projected... more Numerous studies have shown that visual performance critically depends on the stimulus' projected retinal location. For example, performance tends to be better along the horizontal relative to the vertical meridian (lateral anisotropy). Another case is the so-called upper-lower anisotropy, whereby performance is better in the upper relative to the lower hemifield. This study investigates whether temporal order judgments (TOJs) are subject to these visual field constraints. In Experiments 1 and 2, subjects reported the temporal order of two disks located along the horizontal or vertical meridians. Each target disk was surrounded by 10 black and white distractor disks, whose polarity remained unchanged (static condition) or reversed throughout the trial (dynamic condition). Results indicate that the mere presence of dynamic distractors elevated thresholds by more than a factor of four and that this elevation was particularly pronounced along the vertical meridian, evidencing the lateral anisotropy. In Experiment 3, thresholds were compared in upper, lower, left, and right visual hemifields. Results show that the threshold elevation caused by dynamic distractors was greatest in the upper visual field, demonstrating an upper-lower anisotropy. Critically, these anisotropies were evident exclusively in dynamic distractor conditions suggesting that distinct processes govern TOJ performance under these different contextual conditions. We propose that whereas standard TOJs are processed by fast low-order motion mechanisms, the presence of dynamic distractors mask these low-order motion signals, forcing observers to rely more heavily on more sluggish higher order motion processes.

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Orientation-tuned masking and adaptation caused by motion streaks

The oriented trail of blur left by fast-moving objects ('motion streaks') could be used... more The oriented trail of blur left by fast-moving objects ('motion streaks') could be used by the visual system, in combination with motion information, to help judge direction of motion (Geisler, 1999). If fast motion were'deblurred'very early in the motion perception process, however, streaks would be unavailable at the cortical level to combine with motion signals. Here we show that fast-moving arrays of Gaussian blobs cause monoptic contrast masking of static gratings. This is tuned for both orientation and spatial frequency, with similar ...

Temporal order judgments are modality specific: A perceptual learning study

We investigated whether time perception is central and supramodal or peripheral and modality spec... more We investigated whether time perception is central and supramodal or peripheral and modality specific. Subjects trained on temporal order judgments (TOJs) over 10 sessions (sufficient for asymptotic learning). Three groups were trained: visual, auditory, and bimodal. All groups began with pretests to measure TOJ thresholds on various stimuli: visual gratings (0 and 90 orientations), visual position, auditory tones (1 and 4 kHz frequencies), and bimodal (tone/grating) stimuli. Onset and offset TOJs were measured. After training on a ...

Temporal whitening is driven by transient noise

Naturally occurring luminance distributions are approximately 1/f in their spatial and temporal s... more Naturally occurring luminance distributions are approximately 1/f in their spatial and temporal spectra. By systematically varying the spectral profile of spatially and temporally broadband noise stimuli, we demonstrate that humans invariably overestimate the proportion of high spatial and temporal frequency input energy, effectively equalising (whitening) its response to stimuli with naturally occurring low frequency-biased spectra. Additional masking and adaptation experiments support an asymmetric noise account of ...

Spatiotemporal dynamics of coaxial and parallel contrast facilitation suggest distinct mechanisms

Human observers are more sensitive to a foveal Gabor target when it is presented in the context o... more Human observers are more sensitive to a foveal Gabor target when it is presented in the context of collinear and coaxially displaced Gabor flankers than when presented alone (Polat and Sagi, 1993 Vision Research 33 993-999). We examined the dynamics of this surround facilitation by measuring modulation of the target contrast detection threshold at multiple exposure durations and target-flanker separations. The minimum exposure required to induce facilitation (facilitative delay) was found to monotonically increase with target- ...

Critical differences in flicker rate capture attention

Does visual flicker capture attention, and if so, are faster flicker rates more effective? This s... more Does visual flicker capture attention, and if so, are faster flicker rates more effective? This study used a speeded visual search task involving horizontal and vertical target singletons amongst oblique distractors, all equidistantly located around fixation. Oriented elements were surrounded by a luminance modulating annulus. In Experiment 1 distractor annuli all flickered at 1.3 or 12.1 Hz while the target temporal rate varied between 1.3 and 12.1 Hz. Set size was either 4, 7, or 10 items. Search improved monotonically with increasing temporal ...

The time-course of motion streak integration at photopic and scotopic light levels

Perception, 2010

Temporal integration in the visual system causes fast-moving objects to leave oriented 'stre... more Temporal integration in the visual system causes fast-moving objects to leave oriented 'streaks' in their wake which could be used to facilitate motion direction perception (Geisler, 1999 Nature). Temporal integration is thought to occur over 100 ms, although this has never been tested for motion streaks. Here we use fast 'streaky'motion to mask briefly-flashed gratings either parallel or orthogonal to the motion. Gratings were presented at various asynchronies relative to motion onset to reveal the time-course of the accruing streaks. ...

Orientation-dependence of adaptation and masking: Isotropic adaptation fails to transfer between the eyes

Perception, 2010

Female Body Dissatisfaction and Attentional Bias to Body Images Evaluated Using Visual Search

Frontiers in Psychology, 2020

One factor, believed to predict body dissatisfaction is an individual's propensity to attend to c... more One factor, believed to predict body dissatisfaction is an individual's propensity to attend to certain classes of human body image stimuli relative to other classes. These attentional biases have been evaluated using a range of paradigms, including dotprobe, eye-tracking and free view visual search, which have yielded a range of-often contradictory-findings. This study is the first to employ a classic compound visual search task to investigate the relationship between body dissatisfaction and attentional biases to images of underweight and with-overweight female bodies. Seventy-one undergraduate females, varying their degree of body dissatisfaction and Body Mass Index (BMI), searched for a horizontal or vertical target line among tilted lines. A separate female body image was presented within close proximity to each line. On average, faster search times were obtained when the target line was paired with a uniquely underweight or with-overweight body relative to neutral (average weight only) trials indicating that body weight-related images can effectively guide search. This congruent search effect was stronger for individuals with high eating restraint (a behavioral manifestation of body image disturbance) when search involved a uniquely underweight body. By contrast, individuals with high BMIs searched for lines more rapidly when paired with withoverweight rather than underweight bodies, than did individuals with lower BMIs. For incongruent trials-in which a unique body was paired with a distractor rather than the target-search times were indistinguishable from neutral trials, indicating that the deviant bodies neither compulsorily "captured" attention nor reduced participants' ability to disengage their attention from either underweight or with-overweight bodies. These results imply the existence of attentional strategies which reflect one's current body and goal-directed eating behaviors.

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Male Figural Rating Scales: A Critical Review of the Literature

Behaviour Change, 2020

Figural rating scales are tools used to measure male body dissatisfaction. The present review aim... more Figural rating scales are tools used to measure male body dissatisfaction. The present review aimed to examine the design and psychometric properties of male figural rating scales and make recommendations based on findings. Relevant databases were systematically searched for studies that had developed and validated male figural rating scales. Twenty studies were included in this review. Figural rating scales differed in terms of the number of images represented and type of stimuli used (hand-drawn silhouettes, hand-drawn figures, computer-rendered figures, and photograph figures). Reliability and validity evidence varied greatly in strength across all scales. Four of the 20 scales included a correlational analysis between figural rating scale scores and eating disorder symptoms. Results showed the moderate to high positive correlations between eating disorder symptoms and figural rating scale perceived and index scores, suggesting that figural rating scales are sensitive to detectin...

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