A CODE model bridging crowding in sparse and dense displays.

Visual crowding is arguably the strongest limitation imposed on extrafoveal vision, and is a relatively well-understood 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.

Visual crowding: Double dissociation between orientation and brightness judgments.

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.

Changes (but not differences) in motion direction fail to capture attention.

In this study we investigated under what conditions motion direction changes pop out in continuously moving target/distractor environments. Participants were presented with vertically oriented Gabor patches whose carrier components drifted at a constant speed from left to right and then reversed direction. On any given trial, one of these elements was nominated as the target and the remaining elements were distractors. Distractor elements all changed direction simultaneously. The distractors either moved in a homogeneous manner (i.e. all moved in the same direction), or in a heterogeneous manner (i.e. direction was randomized). The target moved with a similar spatio-temporal trajectory as the distractors from left to right (or vice versa), but changed direction asynchronously with respect to the distracting elements. The participants' task was to locate this deviant (target) Gabor patch. We show that a motion direction change pops out (as indicated by the absence of a set size effect) when the surrounding distractors move in a homogeneous direction. When the distractors moved in heterogenous directions, a similar pop out effect was observed when the set size was small (≤5 elements), but not when it was large. This suggests that motion direction changes capture attention only when the change results in a unique direction of motion. Consistent with this finding we also show that a moving target (without direction change) captures attention in cases in which all distractors recently changed direction. This corroborates the idea that, in addition to direction cues, the temporal uniqueness of a change in an object's direction (or absence, thereof) relative to surrounding objects is a cue capable of capturing attention.

The relationship between psychophysical body categorization performance and male body dissatisfaction.

The present study compared the predictive relationship between various psychophysical indices of body categorization performance (Point of Subjective Equivalence (PSE), Just Noticeable Difference (JND) and Reaction Time (RT)) and male body dissatisfaction (Male Body Attitudes Scale (MBAS)) and eating disorder symptoms (Eating disorders examination questionnaire (EDE-Q)), with performance on a validated figure rating scale (Visual Body Scale for Men (VBSM)). Body Mass Index, body fat percentage, and fat free mass index were also measured. PSE was not as sensitive in predicting body dissatisfaction and eating disorder symptoms as the VBSM. JND and average RT were found to be sensitive predictors of body dissatisfaction and eating disorder symptoms across the 82 male participants. JND proved to be a better indicator of weight concern than the VBSM-M. Whilst the body categorization task offers new insights into the way body images may be processed by males with different levels of body dissatisfaction, the VBSM and the conventional self-report measures are likely to be clinically more efficacious at measuring body dissatisfaction.

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

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 dot-probe, 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 with-overweight 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.

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

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.

Visual Body Scale for Men (VBSM): Validation of a new figural rating scale to measure perceived-desired body discrepancy in men.

OBJECTIVES: This study examined the psychometric properties of the Visual Body Scale for Men (VBSM), a new figural rating scale designed as a measure of male perceived-ideal body discrepancy. METHODS: In Study 1, participants were 133 males who selected their perceived and desired bodies from the VBSM. Body composition, body dissatisfaction, eating disorder and depressive symptomatology were obtained. In Study 2, participants were 33 males who completed the VBSM and the Bodybuilder Image Grid (BIG). Study 2 aimed to compare the validity evidence of the VBSM to the BIG. RESULTS: Both VBSM-Body Fat (VBSM-BF) and VBSM-Muscularity (VBSM-M) demonstrated sound test-retest reliability, convergent, concurrent, and discriminant validity evidence. Additionally, the VBSM demonstrated better sensitivity for detecting body fat-related body image and dissatisfaction when compared to the BIG. CONCLUSION: The VBSM improves upon existing male figural rating scales in terms of image quality, includes both dimensions of a male body image, and demonstrates good psychometric properties.

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

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.

Stereoscopic Segmentation Cues Improve Visual Timing Performance in Spatiotemporally Cluttered Environments.

Recently, Cass and Van der Burg demonstrated that temporal order judgment (TOJ) precision could be profoundly impaired by the mere presence of dynamic visual clutter elsewhere in the visual field. This study examines whether presenting target and distractor objects in different depth planes might ameliorate this remote temporal camouflage (RTC) effect. TOJ thresholds were measured under static and dynamic (flickering) distractor conditions. In Experiment 1, targets were presented at zero, crossed, or uncrossed disparity, with distractors fixed at zero disparity. Thresholds were significantly elevated under dynamic compared with static contextual conditions, replicating the RTC effect. Crossed but not uncrossed disparity targets improved performance in dynamic distractor contexts, which otherwise produce substantial RTC. In Experiment 2, the assignment of disparity was reversed: targets fixed at zero disparity; distractors crossed, uncrossed, or zero. Under these conditions, thresholds improved significantly in the nonzero distractor disparity conditions. These results indicate that presenting target and distractor objects in different planes can significantly improve TOJ performance in dynamic conditions. In Experiment 3, targets were each presented with a different sign of disparity (e.g., one crossed and the other uncrossed), with no resulting performance benefits. Results suggest that disparity can be used to alleviate the performance-diminishing effects of RTC, but only if both targets constitute a single and unique disparity-defined surface.

Adaptation-Induced Blindness Is Orientation-Tuned and Monocular.

We examined the recently discovered phenomenon of Adaptation-Induced Blindness (AIB), in which highly visible gratings with gradual onset profiles become invisible after exposure to a rapidly flickering grating, even at very high contrasts. Using very similar stimuli to those in the original AIB experiment, we replicated the original effect across multiple contrast levels, with observers at chance in detecting the gradual onset stimuli at all contrasts. Then, using full-contrast target stimuli with either abrupt or gradual onsets, we tested both the orientation tuning and interocular transfer of AIB. If, as the original authors suggested, AIB were a high-level (perhaps parietally mediated) effect resulting from the 'gating' of awareness, we would not expect the effects of AIB to be tuned to the adapting orientation, and the effect should transfer interocularly. Instead, we find that AIB (which was present only for the gradual onset target stimuli) is both tightly orientation-tuned and shows absolutely no interocular transfer, consistent with a very early cortical locus.

Evolving the keys to visual crowding.

Peripheral vision can be severely impaired by nearby clutter. Decades of research using sparse displays have established that this phenomenon, known as visual crowding, follows Bouma's rule: Interference occurs for target-distractor separations up to half the target's eccentricity. Although considered a fundamental constraint on human vision, it is unclear whether Bouma's rule holds in dense heterogeneous visual environments. Using a genetic algorithm we investigated crowding in densely cluttered displays. Participants were instructed to identify the orientation of a target line (6° eccentricity) among 284 distractor lines. Displays supporting highest accuracy were selected ("survival of the fittest") and combined to create new displays. Performance improved over generations, predominantly driven by the emergence of horizontal flankers within 1° of the near-vertical target, but with no evidence of interference beyond this radius. We conclude that Bouma's rule does not necessarily hold in densely cluttered displays. Instead, a nearest-neighbor segmentation rule provides a better account. (PsycINFO Database Record

Audiovisual temporal recalibration occurs independently at two different time scales.

Combining signals across the senses improves precision and speed of perception, although this multisensory benefit declines for asynchronous signals. Multisensory events may produce synchronized stimuli at source but asynchronies inevitably arise due to distance, intensity, attention and neural latencies. Temporal recalibration is an adaptive phenomenon that serves to perceptually realign physically asynchronous signals. Recently, it was discovered that temporal recalibration occurs far more rapidly than previously thought and does not require minutes of adaptation. Using a classical audiovisual simultaneity task and a series of brief flashes and tones varying in onset asynchrony, perceived simultaneity on a given trial was found to shift in the direction of the preceding trial's asynchrony. Here we examine whether this inter-trial recalibration reflects the same process as prolonged adaptation by combining both paradigms: participants adapted to a fixed temporal lag for several minutes followed by a rapid series of test trials requiring a synchrony judgment. Interestingly, we find evidence of recalibration from prolonged adaptation and inter-trial recalibration within a single experiment. We show a dissociation in which sustained adaptation produces a large but decaying recalibration effect whilst inter-trial recalibration produces large transient effects whose sign matches that of the previous trial.

Stretching time: Relativistic lag-induced shifts in perceived audiovisual synchrony using cluttered displays.

When presented with temporally displaced audiovisual events, observers shift their point of subjective simultaneity (PSS) in the direction of this prior lag. This effect, known as temporal recalibration (TR), has been inferred previously using single audiovisual events. Here we investigate TR using an audiovisual synchrony search paradigm employing spatiotemporally cluttered visual displays. By manipulating the relative modulation frequency of the adaptor (0.72 Hz) and test (0.36, 0.72 Hz) we find that following lag-adaptation, PSS shifts preserve the relative phase-not the latency-of the adapted lag. Applying this cross-frequency design to a classic simultaneity discrimination task, we find TR is unaffected by the relative frequency of adaptor and test in terms of latency rather than phase. This dissociation implies that under conditions of low spatial certainty TR obeys a relativistic (phase-conserving) temporal scaling law, whereas high spatial certainty affords PSS shifts, which operate in absolute (latency-conserving) temporal coordinates.

Evolving the stimulus to fit the brain: a genetic algorithm reveals the brain's feature priorities in visual search.

How does the brain find objects in cluttered visual environments? For decades researchers have employed the classic visual search paradigm to answer this question using factorial designs. Although such approaches have yielded important information, they represent only a tiny fraction of the possible parametric space. Here we use a novel approach, by using a genetic algorithm (GA) to discover the way the brain solves visual search in complex environments, free from experimenter bias. Participants searched a series of complex displays, and those supporting fastest search were selected to reproduce (survival of the fittest). Their display properties (genes) were crossed and combined to create a new generation of "evolved" displays. Displays evolved quickly over generations towards a stable, efficiently searched array. Color properties evolved first, followed by orientation. The evolved displays also contained spatial patterns suggesting a coarse-to-fine search strategy. We argue that this behavioral performance-driven GA reveals the way the brain selects information during visual search in complex environments. We anticipate that our approach can be adapted to a variety of sensory and cognitive questions that have proven too intractable for factorial designs.

Remote temporal camouflage: contextual flicker disrupts perceived visual temporal order.

Correctly perceiving the temporal order of events is essential to many tasks. Despite this, the factors constraining our ability to make timing judgments remain largely unspecified. Here we present a new phenomenon demonstrating that perceived timing of visual events may be profoundly impaired by the mere presence of irrelevant events elsewhere in the visual field. Human observers saw two abrupt luminance events presented across a range of onset asynchronies. Temporal order judgment (TOJ) just noticeable differences (JNDs) provided a behavioural index of temporal precision. When target events were presented in isolation or in static distractor environments temporal resolution was very precise (JNDs ∼20ms). However, when surrounded by dynamic distractor events, performance deteriorated more than a factor of four. This contextual effect we refer to as Remote Temporal Camouflage (RTC) operates across large spatial and temporal distances and possesses a unique spatial distribution conforming to neither the predictions of attentional capture by transient events, nor by stimulus dependencies associated with other contextual phenomena such as surround suppression, crowding, object-substitution masking or motion-induced blindness. We propose that RTC is a consequence of motion-related masking whereby irrelevant motion signals evoked by dynamic distractors interfere with TOJ-relevant target-related apparent motion. Consistent with this we also show that dynamic visual distractors do not interfere with audio-visual TOJs. Not only is RTC the most spatially extensive contextual effect ever reported, it offers vision science a new technique with which to investigate temporal order performance, free of motion-related sensory contributions.

Window of audio-visual simultaneity is unaffected by spatio-temporal visual clutter.

In the present study we investigate the rules governing the perception of audiovisual synchrony within spatio-temporally cluttered visual environments. Participants viewed a ring of 19 discs modulating in luminance while hearing an amplitude modulating tone. Each disc modulated with a unique temporal phase (40 ms intervals), with only one synchronized to the tone. Participants searched for the synchronised disc whose spatial location varied randomly across trials. Square-wave modulation facilitated search: the synchronized disc was frequently chosen, with tight response distributions centred near zero-phase lag. In the sinusoidal condition responses were equally distributed over the 19 discs regardless of phase. To investigate whether subjective synchrony in the square-wave condition was limited by spatial or temporal factors we repeated the experiment with either reduced spatial density (9 discs) or temporal density (80 ms phase intervals). Reduced temporal density greatly facilitated synchrony perception but left the synchrony bandwidth unchanged, while no influence of spatial density was found. We conclude that audio-visual synchrony is not strongly constrained by the spatial or temporal density of the visual display, but by a temporal window within which audio-visual events are perceived as synchronous, with a full bandwidth of ~185 ms.

A dissociation of performance and awareness during binocular rivalry.

When conflicting stimuli are presented to equivalent locations in each eye, people experience binocular rivalry, a phenomenon characterized by alternations in conscious awareness of each eye's image. Attempts at objective measurement using monocular probe-detection methods show that sensitivity to probe stimuli is reduced during periods when those stimuli are reportedly suppressed. But are observers really able to detect stimuli that are perceptually invisible, or does the probe presentation itself reverse rivalry dominance between the two eyes? Here, we measured both judgment accuracy and confidence in those judgments across multiple probe contrast levels, and we found evidence for high accuracy with reduced awareness during suppression that was not due to probe-induced switches in rivalry dominance. This dissociation points to the existence of blindsight-like behavior in normal observers.

Rapid recalibration to audiovisual asynchrony.

To combine information from different sensory modalities, the brain must deal with considerable temporal uncertainty. In natural environments, an external event may produce simultaneous auditory and visual signals yet they will invariably activate the brain asynchronously due to different propagation speeds for light and sound, and different neural response latencies once the signals reach the receptors. One strategy the brain uses to deal with audiovisual timing variation is to adapt to a prevailing asynchrony to help realign the signals. Here, using psychophysical methods in human subjects, we investigate audiovisual recalibration and show that it takes place extremely rapidly without explicit periods of adaptation. Our results demonstrate that exposure to a single, brief asynchrony is sufficient to produce strong recalibration effects. Recalibration occurs regardless of whether the preceding trial was perceived as synchronous, and regardless of whether a response was required. We propose that this rapid recalibration is a fast-acting sensory effect, rather than a higher-level cognitive process. An account in terms of response bias is unlikely due to a strong asymmetry whereby stimuli with vision leading produce bigger recalibrations than audition leading. A fast-acting recalibration mechanism provides a means for overcoming inevitable audiovisual timing variation and serves to rapidly realign signals at onset to maximize the perceptual benefits of audiovisual integration.

Orientation-specificity of adaptation: isotropic adaptation is purely monocular.

Numerous studies have found that prolonged exposure to grating stimuli reduces sensitivity to subsequently presented gratings, most evidently when the orientations of the adapting and test patterns are similar. The rate of sensitivity loss varies with angular difference indicating both the presence and bandwidths of psychophysical 'orientation channels'. Here we study the orientation dependency of contrast adaptation measured both monoptically and dichoptically. Earlier psychophysical reports show that orientation bandwidths are broader at lower spatial frequencies, and we confirm this with a simple von Mises model using 0.25 vs. 2 c.p.d. gratings. When a single isotropic (orientation invariant) parameter is added to this model, however, we find no evidence for any difference in bandwidth with spatial frequency. Consistent with cross-orientation masking effects, we find isotropic adaptation to be strongly low spatial frequency-biased. Surprisingly, unlike masking, we find that the effects of interocular adaptation are purely orientation-tuned, with no evidence of isotropic threshold elevation. This dissociation points to isotropic (or 'cross-orientation') adaptation being an earlier and more magnocellular-like process than that which supports orientation-tuned adaptation and suggests that isotropic masking and adaptation are likely mediated by separate mechanisms.

Disparity-based stereomotion detectors are poorly suited to track 2D motion.

A study was conducted to examine the time required to process lateral motion and motion-in-depth for luminance- and disparity-defined stimuli. In a 2 × 2 design, visual stimuli oscillated sinusoidally in either 2D (moving left to right at a constant disparity of 9 arcmin) or 3D (looming and receding in depth between 6 and 12 arcmin) and were defined either purely by disparity (change of disparity over time [CDOT]) or by a combination of disparity and luminance (providing CDOT and interocular velocity differences [IOVD]). Visual stimuli were accompanied by an amplitude-modulated auditory tone that oscillated at the same rate and whose phase was varied to find the latency producing synchronous perception of the auditory and visual oscillations. In separate sessions, oscillations of 0.7 and 1.4 Hz were compared. For the combined CDOT + IOVD stimuli (disparity and luminance [DL] conditions), audiovisual synchrony required a 50 ms auditory lag, regardless of whether the motion was 2D or 3D. For the CDOT-only stimuli (disparity-only [DO] conditions), we found that a similar lag (~60 ms) was needed to produce synchrony for the 3D motion condition. However, when the CDOT-only stimuli oscillated along a 2D path, the auditory lags required for audiovisual synchrony were much longer: 170 ms for the 0.7 Hz condition, and 90 ms for the 1.4 Hz condition. These results suggest that stereomotion detectors based on CDOT are well suited to tracking 3D motion, but are poorly suited to tracking 2D motion.