L Fademrecht

Action recognition in the visual periphery

Recognizing whether the gestures of somebody mean a greeting or a threat is crucial for social interactions. In real life, action recognition occurs over the entire visual field. In contrast, much of the previous research on action recognition has primarily focused on central vision. Here our goal is to examine what can be perceived about an action outside of foveal vision. Specifically, we probed the valence as well as first level and second level recognition of social actions (handshake, hugging, waving, punching, slapping, and kicking) at 0° (fovea/fixation), 15°, 30°, 45°, and 60° of eccentricity with dynamic (Experiment 1) and dynamic and static (Experiment 2) actions. To assess peripheral vision under conditions of good ecological validity, these actions were carried out by a life-size human stick figure on a large screen. In both experiments, recognition performance was surprisingly high (more than 66% correct) up to 30° of eccentricity for all recognition tasks and followed a nonlinear decline with increasing eccentricities.

Action recognition is viewpoint-dependent in the visual periphery

ABSTRACT Recognizing actions of others across the whole visual field is required for social interactions. In a previous study, we have shown that recognition is very good even when life‐size avatars who were facing the observer carried out actions (e.g. waving) and were presented very far away from the fovea (Fademrecht, Bülthoff, & de la Rosa, 2016). We explored the possibility whether this remarkable performance was owed to life‐size avatars facing the observer, which – according to some social cognitive theories (e.g. Schilbach et al., 2013) – could potentially activate different social perceptual processes as profile facing avatars. Participants therefore viewed a life‐size stick figure avatar that carried out motion‐captured social actions (greeting actions: handshake, hugging, waving; attacking actions: slapping, punching and kicking) in frontal and profile view. Participants’ task was to identify the actions as ‘greeting’ or as ‘attack’ or to assess the emotional valence of the actions. While recognition accuracy for frontal and profile views did not differ, reaction times were significantly faster in general for profile views (i.e. the moving avatar was seen profile on) than for frontal views (i.e. the action was directed toward the observer). Our results suggest that the remarkable well action recognition performance in the visual periphery was not owed to a more socially engaging front facing view. Although action recognition seems to depend on viewpoint, action recognition in general remains remarkable accurate even far into the visual periphery.

Recognition of static and dynamic social actions in the visual periphery

Although actions often appear in the visual periphery, little is known about action recognition outside of the fovea. Our previous results have shown that action recognition of moving life-size human stick figures is surprisingly accurate even in far periphery and declines non-linearly with eccentricity. Here, our aim was (1) to investigate the influence of motion information on action recognition in the periphery by comparing static and dynamic stimuli recognition and (2) to assess whether the observed non-linearity in our previous study was caused by the presence of motion because a linear decline of recognition performance with increasing eccentricity was reported with static presentations of objects and animals (Jebara et al. 2009; Thorpe et al. 2001). In our study, 16 participants saw life-size stick figure avatars that carried out six different social actions (three different greetings and three different aggressive actions). The avatars were shown dynamically and statically on a large screen at different positions in the visual field. In a 2AFC paradigm, participants performed 3 tasks with all actions: (a) They assessed their emotional valence; (b) they categorized each of them as greeting or attack and (c) they identified each of the six actions. We found better recognition performance for dynamic stimuli at all eccentricities. Thus motion information helps recognition in the fovea as well as in far periphery. (2) We observed a non-linear decrease of recognition performance for both static and dynamic stimuli. Power law functions with an exponent of 3.4 and 2.9 described the non-linearity observed for dynamic and static actions respectively. These non-linear functions describe the data significantly better (p=.002) than linear functions and suggest that human actions are processed differently from objects or animals. Meeting abstract presented at VSS 2015.

Two Ways to Facial Expression Recognition? Motor and Visual Information Have Different Effects on Facial Expression Recognition:

Motor-based theories of facial expression recognition propose that the visual perception of facial expression is aided by sensorimotor processes that are also used for the production of the same expression. Accordingly, sensorimotor and visual processes should provide congruent emotional information about a facial expression. Here, we report evidence that challenges this view. Specifically, the repeated execution of facial expressions has the opposite effect on the recognition of a subsequent facial expression than the repeated viewing of facial expressions. Moreover, the findings of the motor condition, but not of the visual condition, were correlated with a nonsensory condition in which participants imagined an emotional situation. These results can be well accounted for by the idea that facial expression recognition is not always mediated by motor processes but can also be recognized on visual information alone.

Action Recognition in a Crowded Environment

So far, action recognition has been mainly examined with small point-light human stimuli presented alone within a narrow central area of the observer’s visual field. Yet, we need to recognize the actions of life-size humans viewed alone or surrounded by bystanders, whether they are seen in central or peripheral vision. Here, we examined the mechanisms in central vision and far periphery (40° eccentricity) involved in the recognition of the actions of a life-size actor (target) and their sensitivity to the presence of a crowd surrounding the target. In Experiment 1, we used an action adaptation paradigm to probe whether static or idly moving crowds might interfere with the recognition of a target’s action (hug or clap). We found that this type of crowds whose movements were dissimilar to the target action hardly affected action recognition in central and peripheral vision. In Experiment 2, we examined whether crowd actions that were more similar to the target actions affected action recognition. Indeed, the presence of that crowd diminished adaptation aftereffects in central vision as wells as in the periphery. We replicated Experiment 2 using a recognition task instead of an adaptation paradigm. With this task, we found evidence of decreased action recognition accuracy, but this was significant in peripheral vision only. Our results suggest that the presence of a crowd carrying out actions similar to that of the target affects its recognition. We outline how these results can be understood in terms of high-level crowding effects that operate on action-sensitive perceptual channels.

Visual processes dominate perception and action during social interactions

Gender differences are well established in cognition and somato-sensation, but there are almost no studies on gender differences in visual perception. One reason is that sample size is often small because effect sizes are large. Small samples are not well suited to test for gender differences. Here, we tested 887 participants from 14 to 90 years old. We tested participants in visual and vernier acuity, visual backward masking and the Wisconsin Card Sorting Test (WCST). We found no gender differences in any of the four tests for younger participants (n = 358; 14–30 years old). Even in a subgroup of schizophrenia patients (n = 260), we did not find gender differences, but large performance deficits in patients compared to controls. For middle-aged participants (n = 170; 31–59 years old), men performed significantly better than women in all perceptual tests, even when we controlled for age. We also found better performance of men compared to women in vernier duration in older participants (n = 99; 60–90 years old) and trends in the same direction for the other tests. Hence, it may be that women’s performance deteriorates with age more strongly than men’s performance. We did not find any difference in WCST, indicating no gender differences for executive functions.Although visual integration is often thought to be retinotopic, visual features can be integrated across retinotopic locations. For example, when a Vernier is followed by a sequence of flanking lines on either side, a percept of two diverging motion streams is elicited. Even though the central Vernier is invisible due to metacontrast masking, its offset is visible in the following elements. If an offset is introduced to one of the flanking lines, the two offsets combine (Otto et al., 2006). Here, by varying the number of flanking lines and the position of the flank offset, we show that this integration lasts up to 450 ms. Furthermore, this process is mandatory, i.e, observers are not able to consciously access the individual lines and change their decision. These results suggest that the contents of consciousness can be modulated by an unconscious memory-process wherein information is integrated for up to 450 ms.The ability of people with Parkinson’s (PwP) to discriminate upright and inverted facial expressions is evaluated using a temporal two-interval forced-choice paradigm. Stimuli are black and white images of neutral, happy, angry, disgusted, fearful, sad and surprised expressions. Inverted stimuli are the two expressions that participants are most and least sensitive to. A range of intensities of expressions (0–100%) are created by morphing between neutral and expressive images. The neutral image (0%) is presented in one interval and the expressive image (varies –100%) in the other. Observers indicate the interval that contained the image that was most expressive. For all upright expressions and all participants, performance increases from chance to 100% correct as intensity of expression increases. Fitted functions describing performance of happy and disgust are shifted to the left of others. This suggests that PwP are most sensitive to expressions of happiness and disgust. PwP and control participants show a small reduction in sensitivity for the expression they are most sensitive to when it is inverted (Face Inversion Effect). For PwP there is a considerable Face Inversion Effect for the expression they are least sensitive to. This suggests that configural face processing is disrupted in Parkinson’s disease.Unlike in cognition, audition and somatosensation, performance between various visual tasks does not correlate. Surprisingly, even tasks that appear similar, like visual acuity and line bisection task do not share much common variance. Similar results were found for visual illusions. For example, the Ebbinghaus and the Muller-Lyer illusions correlate very weakly. The high intra- and inter-observer variability in visual perception is possibly due to perceptual learning, i.e., individual experience shaping perception throughout one’s life time. Here, we studied the relationship between illusion strength and high-level factors such as personality traits (O-Life) and the vividness of mental imagery (VVIQ). In line with previous findings, we found only few correlations between the magnitudes of the visual illusions, despite having high test-retest reliability. More interestingly, we found a high, positive correlation between the magnitude of the Ponzo illusion and vividness of mental imagery. Moreover, the magnitude of the Ponzo illusion was negatively correlated with cognitive disorganization personality trait. These results were specific to the Ponzo-type illusions. Principal component analysis revealed one factor, with high weights mainly on the Ponzo-type illusions, cognitive disorganization and the vividness of mental imagery.Visual backward masking (VBM) is a very sensitive endophenotype of schizophrenia. Masking deficits are highly correlated with reduced EEG amplitudes. In VBM, a target stimulus is followed by a mask, which decreases performance on the target. Here, we investigated the neural correlates of VBM in relatives of schizophrenia patients. We had three conditions: target only and two VBM conditions, with long and short inter-stimulus intervals (ISI). Patients’ performance was impaired, while the relatives performed at the same level as the controls. Interestingly, EEG N1 amplitudes were higher in relatives compared to controls, while they were lower in patients relative to controls as previously reported. For relatives, N1 amplitudes were at the same level in all conditions. For controls and patients, N1 amplitudes increased with task difficult, e.g., amplitudes in the long ISI condition were lower than in short ISI condition. Our results suggest that relatives use a compensation mechanism tuning the brain to maximum performance in all conditions. Since relatives are already at the peak of their activations, increasing the task difficulty does not change brain processing.In crowding, the perception of an object deteriorates in the presence of nearby elements. Obviously, crowding is a ubiquitous phenomenon, since elements are rarely seen in isolation. Despite this ubiquity, there exists no consensus on how to model crowding. In previous experiments, it was shown that the global configuration of the entire stimulus needs to be taken into account. These findings rule out simple pooling models and favor models sensitive to global spatial aspects. In order to further investigate how to incorporate these aspects into models, we tested different types of texture segmentation models such as the Texture Tiling Model, a variation of the LAMINART neural model, a model based on Epitomes, a model based on filtering in the Fourier domain, and several classic neural network models. Across all models, simply capturing regularities in the stimulus does not suffice, as illustrated by a failure of the Fourier analysis model to explain our results. Importantly, we find that models with a grouping mechanism (such as the LAMINART model) work best. However, this grouping may be implemented in different ways, as we will show.Genetic variations of the alpha7 subunit of the nicotinergic acetylcholine receptor gene (CHRNA7) are linked to cognitive deficits in aging and schizophrenia. However, little is known about associations of the CHRNA7 gene with aged-related decline in visual perception. In the present study, we tested whether variations in the alpha7 subunit of the nicotinergic acetylcholine receptor gene (CHRNA7) interact with the perception of coherent motion in healthy aging. We assessed motion coherence for twenty-five older participants (60-73 years) and twenty-six younger participants (20–27 years) for a left/right motion direction discrimination task. A single nucleotide polymorphism (SNP) [rs2337980] of the CHRNA7 was genotyped. Overall, 25 participants were classified as T/C allele carriers (11 older), and 22 participants were classified as C/C (11 older). Only 3 participants were T/T and therefore, this group was excluded from further analysis. Overall, older adults had higher motion coherence thresholds than younger adults.We did not find any age-related associations of motion direction discrimination with the CHRNA7. However, regardless of age group, participants carrying the T/C genotype performed the task significantly better than C/C carriers. Our results therefore, indicate a strong relationship between the nicotinic system and motion perception.Reinforcement learning is a type of supervised learning, where reward is sparse and delayed. For example in chess, a series of moves is made until a sparse reward (win, loss) is issued, which makes it impossible to evaluate the value of a single move. Still, there are powerful algorithms, which can learn from delayed and sparse feedback. In order to investigate how visual reinforcement learning is determined by the structure of the RL-problem, we designed a new paradigm, in which we presented an image and asked human observers to choose an action (pushing one out of a number of buttons). The chosen action leads to the next image until observers achieve a goal image. Different learning situations are determined by the image-action matrix, which creates a so-called environment. We first tested whether humans can utilize information learned from a simple environment to solve more complex ones. Results showed no evidence supporting this hypothesis. We then tested our paradigm on several environments with different graph theoretical features, such as regular vs. irregular environments. We found that humans performed better in environments which contain less image-action pairs to the goal. We tested various RL-algorithms and found them to perform inferior to humans.The first psychotic episode is an important period for prevention of cognitive and social deterioration in schizophrenia. Cognitive deficits are of particular interest since they are evident even before a proper diagnosis can be made. Interestingly, there is a relation between cognitive deficits and social functioning. Here, we investigated the changes in cognitive and social functioning during one year and determined also the association of social functioning with cognitive impairments and psychopathological symptoms in first episode patients. 32 patients with a first psychotic episode and 32 healthy controls were investigated. Cognitive functions such as visual perception, executive functions, sustained attention, were tested with visual backward masking (VBM), the Wisconsin Card Sorting Test (WCST), and the Continuous Performance Test (CPT). Follow up tests were carried out after 6 and 12 months. Social functioning of the patients was evaluated by Health and Outcome Scale (HoNOS). Cognitive functions of patients were impaired compared to the healthy controls in all 3 tests. Performance in the cognitive tests did not change significantly during the year. Treatment compliance, however, improved social and symptom indicators.Even in the absence of neurodegenerative disease, aging strongly affects vision. Whereas optical deficits are well documented, much less is known perceptual deficits. In most perceptual studies, one paradigm is tested and it is usually found that older participants perform worse than younger participants. Implicitly, these results are taken as evidence that all visual functions of an individual decline determined by one factor, with some individuals aging more severly than others. However, this is not true. We tested 131 older participants (mean age 70 years old) and 108 younger participants (mean age 22 years old) in 14 perceptual tests (including motion perception, contrast and orientation sensitivity, biological motion perception) and in 3 cognitive tasks (WCST, verbal fluency and digit span). Young participants performed better than older participants in almost all of the tests. However, within the group of older participants, age did not predict performance, i.e., a participant could have good results in biological motion perception but poor results in orientation discrimination. It seems that there is not a single ‘‘aging’’ factor but many.39th European Conference on Visual Perception (ECVP) 2016 Barcelona LEGEND. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Monday August 29th Poster presentations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Monday August 29th Symposia presentations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71 Monday August 29th Oral presentations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76 Tuesday August 30th Poster presentations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98 Tuesday August 30th Symposia presentations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169 Tuesday August 30th Oral presentations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174 Wednesday August 31th Poster presentations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190 Wednesday August 31th Symposia presentations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 261 Wednesday August 31th Oral presentations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 264 Thursday September 1st Poster presentations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 279 Thursday September 1st Symposia presentations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 351 Thursday September 1st Oral presentations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 353 Author Index. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 370 Perception 2016, Vol. 45(S2) 1–383 ! The Author(s) 2016 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/0301006616671273 pec.sagepub.comYoung adults typically display a processing advantage for the left side of space (‘‘pseudoneglect’’), whereas older adults display no strongly lateralised bias, or indeed a preference towards the right (Benwell et al., 2014; Schmitz & Peigneux, 2011). For young adults, we have recently reported that 5 commonly-used spatial attention tasks (line bisection, landmark, greyscales, gratingscales and lateralised visual detection) all provide stable intra-task measures of bias over time, however no strong inter-task correlations were found (Learmonth et al., 2015). At present there is no systematic evidence for intra- and inter-task consistency in older adults. To investigate this, we tested 22 older adults (mean age ¼ 70.44) on these five tasks, on two different days. Preliminary results show that three of the five tasks (line bisection, landmark and grayscales) seem to provide stable measures over testing sessions, indicating that they measure a consistent property of the spatial attention network. However, as per our previous finding in young adults, there seem to be no significant between-task correlations. Moreover, in contrast to the leftward biases reported in young adults, this elderly age group showed no significant lateral biases on any of the tasks.Estimates if the visual speed of human movements such as hand gestures, facial expressions and locomotion are important during social interactions because they can be used to infer mood and intention. However it is not clear how observers use retinal signals to estimate real-world movement speed. We conducted a series of experiments to investigate adaptation-induced changes in apparent human locomotion speed, to test whether the changes show repulsion of similar speeds or global re-normalisation of all apparent speeds. Participants adapted to videos of walking or running figures at various playback speeds, and then judged the apparent movement speed of subsequently presented test clips. Their task was to report whether each test clip appeared to be faster or slower than a ‘natural’ speed. After adaptation to a slow-motion or fast-forward video, psychometric functions showed that the apparent speed of all test clips changed, becoming faster or slower respectively, consistent with global re-normalisation rather than with repulsion of test speeds close to the adapting speed. The adaptation effect depended on the retinal speed of the adapting stimulus but did not require recognizably human movements.Awareness, focused attention, and task-relevance were thought to be necessary for perceptual learning (PL): a Feature of the Stimulus (FoS) on which participants perform a task is learned, while a task-irrelevant FoS is not learned. This view has been challenged by the discovery of taskirrelevant PL, occurring for subthreshold task-irrelevant stimuli presented at an unattended, peripheral location. Here, we proof further evidence for task-irrelevant PL by showing that it can occur for subthreshold task-irrelevant FoS presented in the fovea (hence spatially attended). Our experiment was divided into 3 stages: pre-test, training, and post-test. During pre- and posttests, participants performed a 3-dot Vernier task and a 3-dot bisection task. During training, participants performed an unrelated task (luminance discrimination) on the same stimulus. The task-irrelevant FoS, manipulated during training, was the position of the middle dot: either a subthreshold left/right offset (Experimental Group) or in perfect alignment with the outer dots (Control Group). The Experimental Group showed performance improvements in the Vernier task but not in the bisection task; while the Control Group showed no effect on performance in either task. We suggest that PL can occur as an effect of mere exposure to a subthreshold taskirrelevant FoS, which is spatially attended.Feature fusion reflects temporal integration. Previous studies mostly employed foveal presentations with no attention manipulation. In this study we examined the effects of sustained spatial attention on temporal integration using feature-fusion with peripheral presentation. We used a typical feature fusion display. A vernier and anti-vernier stimuli (vernier with offset in the opposite direction than the first vernier) were presented in rapid succession in one of 2 possible locations, at 2° of eccentricity. The attended condition involved endogenous attention manipulation achieved through holding the location of the stimuli constant for the whole block (i.e., the stimuli were always presented to the right of the fixation). Thus, in this condition there was no spatial uncertainty. In the unattended condition, the stimuli could appear either to the right or left of the fixation with equal probability, generating spatial uncertainty. We found considerable feature fusion in the attended condition, suggesting that feature fusion can also occur with peripheral presentation. However, no feature fusion was found without attention (i.e., when there was uncertainty regarding the stimuli location), suggesting that spatial attention improves temporal integration. We are currently conducting similar experiments using different attentional cues to manipulate transient attention.Crowding refers to the detrimental effect of nearby elements on target perception. Recently, Harrison and Bex (Curr Biol, 2015) modeled performance in a novel orientation crowding paradigm where observers reported the orientation of a Landolt C presented alone or surrounded by a flanking C. They found that crowding decreased as flanker radius increased, and their model fit these results well. A key prediction of their model is that flankers with each radius, if presented simultaneously, will additively deteriorate performance. However, evidence from other paradigms suggests that presenting several flankers can actually improve performance, if configured to group separately from the target (e.g., Manassi et al., J Vis 2012). Here, we show a similar grouping effect in the orientation crowding paradigm. We tested observers in three conditions: no flanker, one flanker, or five aligned flankers. All of our observers experienced less crowding with five aligned flankers than one flanker, and our reproduction of Harrison and Bex’s model indeed produced the opposite result. Although Harrison and Bex’s model provides a powerful framework to explain some crowding phenomena, a truly unifying model must also account for such grouping effects, as they are likely ubiquitous in everyday environments.

Seeing actions in the fovea influences subsequent action recognition in the periphery

Adaptation to videos of human locomotion (videos recorded from the London Marathon) affects observers’ subsequent perception of human locomotion speed: normal speed test stimuli are perceived as being played in slow-motion after adaptation to fast-forward stimuli and conversely, are perceived as being played in fast-forward after adaptation to slow-motion stimuli. In this study we investigated whether the presence of recognisable human motion in the adapting stimulus is necessary for the effect. The adapting stimuli were spatially scrambled: horizontal pixel rows were randomly shuffled. The same shuffled order was used for all frames preserving horizontal motion information, but ensuring no human form could be recognised. Results showed that the after-effect persisted despite spatially scrambling the adapting stimuli; human motion is not a necessary requirement for the locomotion after-effect. The after-effect seems to be driven by adaptation in relatively low-level visual channels rather than the high-level processes that encode human motion.Perception is usually non-retinotopic. For example, a reflector on the wheel of a bicycle is perceived to rotate on a circular orbit, while its retinotopic motion is cycloidal. To investigate non-retinotopic motion perception, we used the Ternus-Pikler display. Two disks are repeatedly flashed on a computer screen. A dot moves linearly up-down in the left disk and left-right in the right disk (retinotopic percept). If a third disk is added alternatingly to the left and right, the three disks form a group moving predictably back and forth horizontally. The dot in the central disk now appears to move on a circular orbit (non-retinotopic percept), because the brain subtracts the horizontal group motion from the up-down and left-right motion. Here, we show that predictability is not necessary to compute non-retinotopic motion. In experiment 1, the three disks moved randomly in any direction. In experiment 2, we additionally varied the shape and contrast polarity of the stimuli from frame to frame. In both cases, strong non-retinotopic rotation was perceived. Hence, the visual system can flexibly solve the non-retinotopic motion correspondence problem, even when the retinotopic reference motion is unpredictable and no efference copy-like signals can be used.In Object Substitution Masking (OSM) a mask surrounding, simultaneously onsetting with, and trailing a target leads to a reduction in target perceptibility (Di Lollo et al., 2000). It has been questioned whether this process is due to target substitution or the addition of noise to the percept (Podor, 2012). Two experiments examined this issue using an adjustment task in which a test Landolt C is presented and participants rotate it to match the target Landolt C shown during the trial (typical OSM paradigms use 2-4 alternative forced choice); the dependent measure was the angle of error. In Experiment 1 the effect of a trailing OSM mask (80ms-320ms) is compared against that of adding stimulus noise of varying densities (25%-75%) to the target location. Both manipulations (OSM, stimulus noise) produced a similar change in the distribution of errors compared against a baseline (0ms trailing mask, 0%-noise). The pattern is consistent with both mask manipulations reducing the fidelity of the target percept. In Experiment 2 the OSM and stimulus noise manipulations were varied factorially. Here the two manipulations had combinatorial effects on the error distribution. Implications are discussed regarding the mechanisms of OSM and the consequences of OSM for target perceptionDistributed representations (DR) of cortical channels are pervasive in models of spatio-temporal vision. A central idea that underpins current innovations of DR stems from the extension of 1-D phase into 2-D images. Neurophysiological evidence, however, provides tenuous support for a quadrature representation in the visual cortex, since even phase visual units are associated with broader orientation tuning than odd phase visual units (J.Neurophys.,88,455–463, 2002). We demonstrate that the application of the steering theorems to a 2-D definition of phase afforded by the Riesz Transform (IEEE Trans. Sig. Proc., 49, 3136–3144), to include a Scale Transform, allows one to smoothly interpolate across 2-D phase and pass from circularly symmetric to orientation tuned visual units, and from more narrowly tuned odd symmetric units to even ones. Steering across 2-D phase and scale can be orthogonalized via a linearizing transformation. Using the tiltafter effect as an example, we argue that effects of visual adaptation can be better explained by via an orthogonal rather than channel specific representation of visual units. This is because of the ability to explicitly account for isotropic and cross-orientation adaptation effect from the orthogonal representation from which both direct and indirect tilt after-effects can be explained.claims surround the effects of colour on performance. Elliot, Maier, Moller, Friedman and Meinhardt (2007) proposed that in an achievement context (e.g. maths test) the perception of red impedes performance by inducing avoidance motivation. However, replications of the effect are scant, especially in the UK and some suffer from a lack of stimulus colour control. We report five experiments that attempt to replicate the red-effect in an achievement context across a range of settings: online; in school classrooms; and in the laboratory. In each experiment, stimuli were carefully specified and calibrated to ensure that they varied in hue but not luminance or saturation. Only one experiment replicated the red effect – participants who were primed with a red stimulus (relative to white) for 5 s scored worse on a subsequent verbal task. However, replication and extension of this experiment failed to reproduce the effect. Explanations for the findings are discussed including: the effect is not present in a UK population; the effect requires very specific methodology; the effect does not generalise to applied settings; and/or the original body of work overestimates the prevalence of these effects. PhD research funded by studentship provided by the University of Surrey Psychology Faculty.This poster was presented at 38th European Conference on Visual Perception (ECVP) 2015 Liverpool, abstract published in Perception on 21 August 2015Dynamic stimuli capture attention, even if not in the focus of endogenous attention. Such a stimulus is apparent motion, given that it benefits perception of targets in the motion path. These benefits have been attributed to motion-induced ‘entrainment’ of attention to expected locations (spatial extrapolation) and/or expected time-points (temporal entrainment). Here, we studied the automatic nature of spatial extrapolation versus temporal entrainment with apparent motion stimuli, when motion was task-irrelevant. Participants performed an endogenously cued target detection task, in which symbolic cues prompted attention shifts to lateralized target positons (75% validity). Simultaneously, apparent motion cues flickered either rhythmically or arhythmically across the screen, such that targets appeared either in or out of motion trajectory. Although the motion cue can be considered a distractor (non-informative as to target location), motion direction influenced target detection, which is in line with automatic extrapolation of spatial positions during apparent motion. An effect that was independent and additive to the endogenous cueing benefit. Importantly, temporal cueing in the motion stream also influenced target detection. However, this effect was independent of reflexive motion-cueing to spatial positions. We conclude that spatial extrapolation and temporal entrainment of attention by apparent motion are governed by partially independent reflexive mechanisms.How do interpersonal behavioural dynamics predict individual and joint decisions? Recent interactionist views on social cognition suggest that the most under-studied and important aspect of social cognition may be interaction dynamics. However, it has hitherto proven extremely difficult to devise a controlled setup in which social cues, such as eye gaze, are subject to unconstrained interaction. To address these issues, we use a dual interactive eye-tracking paradigm. Participants are presented with the face of an anthropomorphic avatar, the eye movements of which are linked in real-time to another participant’s eye-gaze. This allows for control of interaction aspects that are not related to the experience of gaze contingency. Participants have to choose which one out of two spheres on either side of the avatar face is the largest. These spheres can have a medium, small, and no difference. Specifically in the latter condition, gaze dynamics guide choices. Using cross-recurrence quantification, we analyse the time course of the gaze interactions and look at how this predicts individual and joint decisions about sphere size, which participant will follow the other, and assess collaboration in a subsequent “stag hunt” game, a variation on the prisoner’s dilemma game.We report a new after-effect of visual motion in which the apparent speed of human locomotion is affected by prior exposure to speeded-up or slowed-down motion. In each trial participants were shown short video clips of running human figures (recorded from the London Marathon) and asked to report whether the speed of movement was ‘slower than natural’ or ‘faster than natural’, by pressing one of two response buttons. The clips were displayed at different playback speeds ranging from slow-motion (0.48x natural speed) to fast-forward (1.44x natural speed). Adaptation to stimuli played at normal speed resulted in the P50 of the psychometric function falling close to normal-speed playback. However after adaptation to 1.44x playback, normal-speed playback appeared too slow, so the P50 shifted significantly towards a higher playback speed; after adaptation to 0.48xplayback, normal-speed playback appeared too fast, so the P50 shifted significantly towards a lower playback speed. The shifts in apparent speed were obtained using both same- and opposite-direction adaptation-test stimulus pairs, indicating that the effect is a speed adaptation effect rather than a directional velocity after-effect. These findings are consistent with norm-based coding of the speed of movement.Young adults typically display a processing advantage for the left side of space (‘‘pseudoneglect’’) but older adults display either no strongly lateralised bias or a preference towards the right (Benwell et al., 2014; Schmitz & Peigneux, 2011). We have previously reported an additive rightward shift in the spatial attention vector with decreasing landmark task line length and increasing age (Benwell et al., 2014). However there is very little neuroimaging evidence to show how this change is represented at a neural level. We tested 20 young (18–25) and 20 older (60–80) adults on long vs short landmark lines whilst recording activity using EEG. The peak ‘‘line length effect’’ (long vs short lines) was localised to the right parieto-occipital cortex (PO4) 137 ms post-stimulus. Importantly, older adults showed additional involvement of left frontal regions (AF3: 386 ms & F7: 387 ms) for short lines only, which may represent the neural correlate of this rightward shift. These behavioural results align with the HAROLD model of aging (Cabeza, 2002) where brain activity becomes distributed across both hemispheres in older adults to support successful performance.We studied the effect of age on visual perceptual decisions of bi-stable stimuli. We used two different stimuli: bi-stable rotating spheres and a binocular rivalry stimulus. At onset, both stimuli can evoke two different percepts: for the sphere clockwise or anti-clockwise rotation and for the binocular rivalry stimulus a percept that switches between the stimuli in the two eyes. The stimuli were presented intermittently for 1 second with a range of inter-stimulus intervals (0.1 – 2 seconds). Subjects ranged between 18 and 73 years old and were instructed to indicate which of the two percepts dominate at each onset of the bi-stable stimulus. Our results show that perceptual choices are more stable for older subjects for the binocular rivalry stimulus and not for the bi-stable rotating spheres. The results will be discussed in the context of current models for bi-stable visual perception.The visual system combines spatial signals from the two eyes to achieve single vision. But if binocular disparity is too large, this perceptual fusion gives way to diplopia. We studied and modelled the processes underlying fusion and the transition to diplopia. The likely basis for fusion is linear summation of inputs onto binocular cortical cells. Previous studies of perceived position, contrast matching and contrast discrimination imply the computation of a dynamicallyweighted sum, where the weights vary with relative contrast. For gratings, perceived contrast was almost constant across all disparities, and this can be modelled by allowing the ocular weights to increase with disparity (Zhou, Georgeson & Hess, 2014). However, when a single Gaussian-blurred edge was shown to each eye perceived blur was invariant with disparity (Georgeson & Wallis, ECVP 2012) – not consistent with linear summation (which predicts that perceived blur increases with disparity). This blur constancy is consistent with a multiplicative form of combination (the contrast-weighted geometric mean) but that is hard to reconcile with the evidence favouring linear combination. We describe a 2-stage spatial filtering model with linear binocular combination and suggest that nonlinear output transduction (eg. ‘half-squaring’) at each stage may account for the blur constancy.

A matter of perspective: action recognition depends on stimulus orientation in the periphery

Bayesian Inference on psychometric functions. The method is fast and convenient to use. Furthermore, we provide suitable defaults for all common settings. By fitting a beta-binomial model our method exhibits increased robustness against nonstationary behaviour caused, e.g., by fluctuations in attention or learning. We performed extensive simulations to validate our method and software implementation. Finally we provide generic methods to compare several psychometric functions statistically. All methods are freely available:
 https://github.com/wichmann-lab/psignifitPsychophysical methodology is used to evaluate the strength of the visual signals contained in facial expressions. Stimuli were black and white images of faces expressing a neutral, positive (happy) or negative affect (e.g. fear or anger). A range of signal strengths (0-100%) of expressions were created by morphing the neutral and expressive images. Stimuli were presented for 200ms in a temporal two-interval forced-choice paradigm. One interval contained the neutral face (0%) and the other the expressive face (varied from 0 – 100%). Observers indicated the interval that contained the image that was more expressive. This emotion detection task showed that observers were more sensitive to happy compared with fearful expressions. This indicates that the emotion signals conveyed by a happy face are more salient than those conveyed by a fearful face. Future research on emotion recognition should consider using psychophysical methodology to perceptually equate stimuli with different expressions. This will remove signal strength as a possible confound.