Investigating distortions in perceptual stability during different self-movements using virtual reality.

Using immersive virtual reality (the HTC Vive Head Mounted Display), we measured both bias and sensitivity when making judgements about the scene stability of a target object during both active (self-propelled) and passive (experimenter-propelled) observer movements. This was repeated in the same group of 16 participants for three different observer-target movement conditions in which the instability of a target was yoked to the movement of the observer. We found that in all movement conditions that the target needed to move with (in the same direction) as the participant to be perceived as scene-stable. Consistent with the presence of additional available information (efference copy) about self-movement during active conditions, biases were smaller and sensitivities to instability were higher in these relative to passive conditions. However, the presence of efference copy was clearly not sufficient to completely eliminate the bias and we suggest that the presence of additional visual information about self-movement is also critical. We found some (albeit limited) evidence for correlation between appropriate metrics across different movement conditions. These results extend previous findings, providing evidence for consistency of biases across different movement types, suggestive of common processing underpinning perceptual stability judgements.

The impact of choice discriminability and outcome valence on visual decision making under risk.

Much of human activity involves perceptual or perceptuo-motor choice between options with uncertain outcomes. Previous research suggests that decisions in these contexts can be near-optimal in some circumstances but can also be significantly biased. Here we investigate how biases might depend on: i) discriminability of available choice outcomes, adjusted by manipulating the Expected Value (EV) function curvature; ii) outcome valence, which changes the tendency for risk seeking/aversive behaviour in cognitive decision making. In three experiments, participants set the size of a catcher in order to catch a dot moving on a random walk (with varying levels of predictability) after it emerged from behind an occluder. Catching and missing the dot were associated with scoring a variable number of outcome points depending on catcher size. In experiment 1 outcomes were most discriminable (high EV curvature) and catcher size settings were near-optimal. In experiments 2 and 3 outcomes were harder to discriminate (low EV curvature) and there was a significant bias to set the catcher size too small. Unlike cognitive decision making, the valence manipulation had little effect. Subsequent analyses suggest observed biases might reflect participants moving settings towards the region with highest EV curvature, where feedback is most informative. These data suggest that: i) unlike cognitive decisions, in this task choices are largely insensitive to outcome valence; ii) EV curvature is potentially an important factor when interpreting performance in such tasks; iii) Choice may be biased towards high EV curvature regions, consistent with value being placed on exploration to increase information return.

The effect of eccentricity on the linear-radial speed bias: Testing the motion-in-depth model.

Radial motion is perceived as faster than linear motion when local spatiotemporal properties are matched. This radial speed bias (RSB) is thought to occur because radial motion is partly interpreted as motion-in-depth. Geometry dictates that a fixed amount of radial expansion at increasing eccentricities is consistent with smaller motion in depth, so it is perhaps surprising that the impact of eccentricity on RSB has not been examined. With this issue in mind, across 3 experiments we investigated the RSB as a function of eccentricity. In a 2IFC task, participants judged which of a linear (test - variable speed) or radial (reference - 2 or 4°/s) stimulus appeared to move faster. Linear and radial stimuli comprised 4 Gabor patches arranged left, right, above and below fixation at varying eccentricities (3.5°-14°). For linear stimuli, Gabors all drifted left or right, whereas for radial stimuli Gabors drifted towards or away from the centre. The RSB (difference in perceived speeds between matched linear and radial stimuli) was recovered from fitted psychometric functions. Across all 3 experiments we found that the RSB decreased with eccentricity but this tendency was less marked beyond 7° - i.e. at odds with the geometry, the effect did not continue to decrease as a function of eccentricity. This was true irrespective of whether stimuli were fixed in size (Experiment 1) or varied in size to account for changes in spatial scale across the retina (Experiment 2). It was also true when we removed conflicting stereo cues via monocular viewing (Experiment 3). To further investigate our data, we extended a previous model of speed perception, which suggests perceived motion for such stimuli reflects a balance between two opposing perceptual interpretations, one for motion in depth and the other for object deformation. We propose, in the context of this model, that our data are consistent with placing greater weight on the motion in depth interpretation with increasing eccentricity and this is why the RSB does not continue to reduce in line with purely geometric constraints.

Collinear facilitation and contour integration in autistic adults: Examining lateral and feedback connectivity.

Alongside difficulties with communication and social interaction, autism is often accompanied by unusual sensory and perceptual experiences including enhanced visual performance on tasks that involve separating local parts from global context. This superiority may be the result of atypical integrative processing, involving feedback and lateral connections between visual neurons. The current study investigated the integrity of these connections in autistic adults by examining two psychophysics tasks that rely on these processes - collinear facilitation and contour integration. The relative contribution of feedback and lateral connectivity was studied by altering the timing of the target relative to the flankers in the collinear facilitation task, in 16 autistic and 16 non-autistic adults. There were no significant differences in facilitation between the autistic and non-autistic groups, indicating that for this task and participant sample, lateral and feedback connectivity appear relatively intact in autistic individuals. Contour integration was examined in a different group of 20 autistic and 18 non-autistic individuals, for open and closed contours to assess the closure effect (improved detection of closed compared to open contours). Autistic individuals showed a reduced closure effect at both short (150 ms) and longer (500 ms) stimulus presentation durations that was driven by better performance of the autistic group for the open contours. These results suggest that reduced closure in a simple contour detection paradigm is unlikely to be due to slower global processing. Reduced closure has implications for understanding sensory overload by contributing to reduced figure-ground segregation of salient visual features.

Detection of scene-relative object movement and optic flow parsing across the adult lifespan.

Moving around safely relies critically on our ability to detect object movement. This is made difficult because retinal motion can arise from object movement or our own movement. Here we investigate ability to detect scene-relative object movement using a neural mechanism called optic flow parsing. This mechanism acts to subtract retinal motion caused by self-movement. Because older observers exhibit marked changes in visual motion processing, we consider performance across a broad age range (N = 30, range: 20-76 years). In Experiment 1 we measured thresholds for reliably discriminating the scene-relative movement direction of a probe presented among three-dimensional objects moving onscreen to simulate observer movement. Performance in this task did not correlate with age, suggesting that ability to detect scene-relative object movement from retinal information is preserved in ageing. In Experiment 2 we investigated changes in the underlying optic flow parsing mechanism that supports this ability, using a well-established task that measures the magnitude of globally subtracted optic flow. We found strong evidence for a positive correlation between age and global flow subtraction. These data suggest that the ability to identify object movement during self-movement from visual information is preserved in ageing, but that there are changes in the flow parsing mechanism that underpins this ability. We suggest that these changes reflect compensatory processing required to counteract other impairments in the ageing visual system.

The Effect of Ageing on Optimal Integration of Conflicting and Non-Conflicting Visual-Haptic Stimuli.

Multisensory integration typically follows the predictions of a statistically optimal model whereby the contribution of each sensory modality is weighted according to its reliability. Previous research has shown that multisensory integration is affected by ageing, however it is less certain whether older adults follow this statistically optimal model. Additionally, previous studies often present multisensory cues which are conflicting in size, shape or location, yet naturally occurring multisensory cues are usually non-conflicting. Therefore, the mechanisms of integration in older adults might differ depending on whether the multisensory cues are consistent or conflicting. In the current experiment, young ( n = 21) and older ( n = 30) adults were asked to make judgements regarding the height of wooden blocks using visual, haptic or combined visual-haptic information. Dual modality visual-haptic blocks could be presented as equal or conflicting in size. Young and older adults' size discrimination thresholds (i.e., precision) were not significantly different for visual, haptic or visual-haptic cues. In addition, both young and older adults' discrimination thresholds and points of subjective equality did not follow model predictions of optimal integration, for both conflicting and non-conflicting cues. Instead, there was considerable between subject variability as to how visual and haptic cues were processed when presented simultaneously. This finding has implications for the development of multisensory therapeutic aids and interventions to assist older adults with everyday activities, where these should be tailored to the needs of each individual.

Visual-tactile selective attention in autism spectrum condition: An increased influence of visual distractors.

We have previously observed that participants with autism spectrum condition (ASC) are more influenced by visual distractors during a tactile task compared with controls (Poole, Gowen, Warren, & Poliakoff, 2015). This finding suggests that changes in multisensory processing could underpin differences in sensory reactivity in ASC. Here we explore the cognitive mechanisms underlying this effect. Adults with ASC (n = 22) and matched neurotypical (NT) controls (n = 22) completed 3 tasks involving similar stimuli. In Experiment 1, we again showed that when participants with ASC were performing a tactile task they were distracted more by visual stimuli compared with NTs. In Experiment 2, however, no differences between the groups were observed on an alternative visual-tactile task (temporal order judgment) requiring attention to both the stimuli. That is, ASC performance was typical when the task did not require the visual stimuli to be suppressed. Furthermore, in Experiment 3 the effects of visual distractors were comparable between the groups when the tactile target was replaced with a visual target. When comparing performance across Experiments 1 and 3, NT participants were better able to suppress visual distractors when the target was tactile than when the target was visual (Experiment 1 vs. 3), but this crossmodal benefit was not observed in participants with ASC. The effects of visual distractors were comparable regardless of the target modality suggesting that the efficacy of visual-tactile selective attention may be reduced in ASC. (PsycINFO Database Record

The Primary Role of Flow Processing in the Identification of Scene-Relative Object Movement.

Retinal image motion could be due to the movement of the observer through space or an object relative to the scene. Optic flow, form, and change of position cues all provide information that could be used to separate out retinal motion due to object movement from retinal motion due to observer movement. In Experiment 1, we used a minimal display to examine the contribution of optic flow and form cues. Human participants indicated the direction of movement of a probe object presented against a background of radially moving pairs of dots. By independently controlling the orientation of each dot pair, we were able to put flow cues to self-movement direction (the point from which all the motion radiated) and form cues to self-movement direction (the point toward which all the dot pairs were oriented) in conflict. We found that only flow cues influenced perceived probe movement. In Experiment 2, we switched to a rich stereo display composed of 3D objects to examine the contribution of flow and position cues. We moved the scene objects to simulate a lateral translation and counter-rotation of gaze. By changing the polarity of the scene objects (from light to dark and vice versa) between frames, we placed flow cues to self-movement direction in opposition to change of position cues. We found that again flow cues dominated the perceived probe movement relative to the scene. Together, these experiments indicate the neural network that processes optic flow has a primary role in the identification of scene-relative object movement.SIGNIFICANCE STATEMENT Motion of an object in the retinal image indicates relative movement between the observer and the object, but it does not indicate its cause: movement of an object in the scene; movement of the observer; or both. To isolate retinal motion due to movement of a scene object, the brain must parse out the retinal motion due to movement of the eye ("flow parsing"). Optic flow, form, and position cues all have potential roles in this process. We pitted the cues against each other and assessed their influence. We found that flow parsing relies on optic flow alone. These results indicate the primary role of the neural network that processes optic flow in the identification of scene-relative object movement.

A re-examination of "bias" in human randomness perception.

Human randomness perception is commonly described as biased. This is because when generating random sequences humans tend to systematically under- and overrepresent certain subsequences relative to the number expected from an unbiased random process. In a purely theoretical analysis we have previously suggested that common misperceptions of randomness may actually reflect genuine aspects of the statistical environment, once cognitive constraints are taken into account which impact on how that environment is actually experienced (Hahn & Warren, Psychological Review, 2009). In the present study we undertake an empirical test of this account, comparing human-generated against unbiased process-generated binary sequences in two experiments. We suggest that comparing human and theoretically unbiased sequences using metrics reflecting the constraints imposed on human experience provides a more meaningful picture of lay people's ability to perceive randomness. Finally, we propose a simple generative model of human random sequence generation inspired by the Hahn and Warren account. Taken together our results question the notion of bias in human randomness perception. (PsycINFO Database Record

Peripheral Visual Cues Contribute to the Perception of Object Movement During Self-Movement.

Safe movement through the environment requires us to monitor our surroundings for moving objects or people. However, identification of moving objects in the scene is complicated by self-movement, which adds motion across the retina. To identify world-relative object movement, the brain thus has to 'compensate for' or 'parse out' the components of retinal motion that are due to self-movement. We have previously demonstrated that retinal cues arising from central vision contribute to solving this problem. Here, we investigate the contribution of peripheral vision, commonly thought to provide strong cues to self-movement. Stationary participants viewed a large field of view display, with radial flow patterns presented in the periphery, and judged the trajectory of a centrally presented probe. Across two experiments, we demonstrate and quantify the contribution of peripheral optic flow to flow parsing during forward and backward movement.

The Effect of Expected Value on Attraction Effect Preference Reversals.

The attraction effect shows that adding a third alternative to a choice set can alter preference between the original two options. For over 30 years, this simple demonstration of context dependence has been taken as strong evidence against a class of parsimonious value-maximising models that evaluate alternatives independently from one another. Significantly, however, in previous demonstrations of the attraction effect alternatives are approximately equally valuable, so there was little consequence to the decision maker irrespective of which alternative was selected. Here we vary the difference in expected value between alternatives and provide the first demonstration that, although extinguished with large differences, this theoretically important effect persists when choice between alternatives has a consequence. We use this result to clarify the implications of the attraction effect, arguing that although it robustly violates the assumptions of value-maximising models, it does not eliminate the possibility that human decision making is optimal.

Contrast effects on speed perception for linear and radial motion.

Speed perception is vital for safe activity in the environment. However, considerable evidence suggests that perceived speed changes as a function of stimulus contrast, with some investigators suggesting that this might have meaningful real-world consequences (e.g. driving in fog). In the present study we investigate whether the neural effects of contrast on speed perception occur at the level of local or global motion processing. To do this we examine both speed discrimination thresholds and contrast-dependent speed perception for two global motion configurations that have matched local spatio-temporal structure. Specifically we compare linear and radial configurations, the latter of which arises very commonly due to self-movement. In experiment 1 the stimuli comprised circular grating patches. In experiment 2, to match stimuli even more closely, motion was presented in multiple local Gabor patches equidistant from central fixation. Each patch contained identical linear motion but the global configuration was either consistent with linear or radial motion. In both experiments 1 and 2, discrimination thresholds and contrast-induced speed biases were similar in linear and radial conditions. These results suggest that contrast-based speed effects occur only at the level of local motion processing, irrespective of global structure. This result is interpreted in the context of previous models of speed perception and evidence suggesting differences in perceived speed of locally matched linear and radial stimuli.

Individual differences in the dynamics of collinear facilitation?

Collinear facilitation refers to the increase in sensitivity found for a target when aligned between nearby, brighter flankers. Many studies have explored the spatial and temporal aspects of this arrangement, and there is a consensus that two mechanisms could be responsible for this phenomenon; lateral excitation within V1 and extra-striate feedback to V1. There is some debate as to whether facilitation can still occur if the target is presented before the flankers, a manipulation known as backward masking, which could rely on feedback to V1. We shed light on this debate by using forward, simultaneous and backward masking with a relatively large sample of 26 participants. We used short stimulus presentation times (35ms) and a range of SOAs (stimulus onset asynchronies) (-70, -35, 0, 35 and 70ms) in order to isolate any feedback facilitation that may occur. We found that collinear facilitation occurred with forward masking (+ve SOAs) in all participants. However, facilitation with backward masking (-ve SOAs) only occurred in 54% of participants. We present a basic model of facilitation that simulates the results of our experiment and could account for differences between previous studies. The model indicates that facilitation with backward masking arises primarily from feedback excitation. Our findings suggest that both lateral connectivity and extra-striate feedback contribute to target facilitation, but in fundamentally different ways and that feedback may be significantly reduced in some participants.

Who "believes" in the Gambler's Fallacy and why?

Humans possess a remarkable ability to discriminate structure from randomness in the environment. However, this ability appears to be systematically biased. This is nowhere more evident than in the Gambler's Fallacy (GF)-the mistaken belief that observing an increasingly long sequence of "heads" from an unbiased coin makes the occurrence of "tails" on the next trial ever more likely. Although the GF appears to provide evidence of "cognitive bias," a recent theoretical account (Hahn & Warren, 2009) has suggested the GF might be understandable if constraints on actual experience of random sources (such as attention and short term memory) are taken into account. Here we test this experiential account by exposing participants to 200 outcomes from a genuinely random (p = .5) Bernoulli process. All participants saw the same overall sequence; however, we manipulated experience across groups such that the sequence was divided into chunks of length 100, 10, or 5. Both before and after the exposure, participants (a) generated random sequences and (b) judged the randomness of presented sequences. In contrast to other accounts in the literature, the experiential account suggests that this manipulation will lead to systematic differences in postexposure behavior. Our data were strongly in line with this prediction and provide support for a general account of randomness perception in which biases are actually apt reflections of environmental statistics under experiential constraints. This suggests that deeper insight into human cognition may be gained if, instead of dismissing apparent biases as failings, we assume humans are rational under constraints. (PsycINFO Database Record

Similarities in Autistic and Neurotypical Visual-Haptic Perception When Making Judgements About Conflicting Sensory Stimuli.

A number of studies have shown that multisensory performance is well predicted by a statistically optimal maximum likelihood estimation (MLE) model. Under this model unisensory estimates are combined additively and weighted according to relative reliability. Recent theories have proposed that atypical sensation and perception commonly reported in autism spectrum condition (ASC) may result from differences in the use of reliability information. Furthermore, experimental studies have indicated that multisensory processing is less effective in those with the condition in comparison to neurotypical (NT) controls. In the present study, adults with ASC (n=13) and a matched NT group (n=13) completed a visual-haptic size judgement task (cf. Gori et al., 2008) in which participants compared the height of wooden blocks using either vision or haptics, and in a dual modality condition in which visual-haptic stimuli were presented in size conflict. Participants with ASC tended to produce more reliable estimates than the NT group. However, dual modality performance was not well predicted by the MLE model for either group. Performance was subsequently compared to alternative models in which the participant either switched between modalities trial to trial (rather than integrating) and a model of non-optimal integration. Performance of both groups was statistically comparable to the cue-switching model. These findings suggest that adults with ASC adopted a similar strategy to NTs when processing conflicting visual-haptic information. Findings are discussed in relation to multisensory perception in ASC and methodological considerations associated with multisensory conflict paradigms.

Brief Report: Which Came First? Exploring Crossmodal Temporal Order Judgements and Their Relationship with Sensory Reactivity in Autism and Neurotypicals.

Previous studies have indicated that visual-auditory temporal acuity is reduced in children with autism spectrum conditions (ASC) in comparison to neurotypicals. In the present study we investigated temporal acuity for all possible bimodal pairings of visual, tactile and auditory information in adults with ASC (n = 18) and a matched control group (n = 18). No group differences in temporal acuity for crossmodal stimuli were observed, suggesting that this may be typical in adults with ASC. However, visual-tactile temporal acuity and bias towards vision when presented with visual-auditory information were both predictors of self-reported sensory reactivity. This suggests that reduced multisensory temporal acuity and/or attention towards vision may contribute to atypical sensory reactivity.

Why contextual preference reversals maximize expected value.

Contextual preference reversals occur when a preference for one option over another is reversed by the addition of further options. It has been argued that the occurrence of preference reversals in human behavior shows that people violate the axioms of rational choice and that people are not, therefore, expected value maximizers. In contrast, we demonstrate that if a person is only able to make noisy calculations of expected value and noisy observations of the ordinal relations among option features, then the expected value maximizing choice is influenced by the addition of new options and does give rise to apparent preference reversals. We explore the implications of expected value maximizing choice, conditioned on noisy observations, for a range of contextual preference reversal types-including attraction, compromise, similarity, and phantom effects. These preference reversal types have played a key role in the development of models of human choice. We conclude that experiments demonstrating contextual preference reversals are not evidence for irrationality. They are, however, a consequence of expected value maximization given noisy observations. (PsycINFO Database Record

Adapting the Crossmodal Congruency Task for Measuring the Limits of Visual-Tactile Interactions Within and Between Groups.

The crossmodal congruency task (CCT) is a commonly used paradigm for measuring visual-tactile interactions and how these may be influenced by discrepancies in space and time between the tactile target and visual distractors. The majority of studies which have used this paradigm have neither measured, nor attempted to control, individual variability in unisensory (tactile) performance. We have developed a version of the CCT in which unisensory baseline performance is constrained to enable comparisons within and between participant groups. Participants were instructed to discriminate between single and double tactile pulses presented to their dominant hand, at their own approximate threshold level. In Experiment 1, visual distractors were presented at -30 ms, 100 ms, 200 ms and 400 ms stimulus onset asynchronies. In Experiment 2, ipsilateral visual distractors were presented 0 cm, 21 cm, and 42 cm vertically from the target hand, and 42 cm in a symmetrical, contralateral position. Distractors presented -30 ms and 0 cm from the target produced a significantly larger congruency effect than at other time points and spatial locations. Thus, the typical limits of visual-tactile interactions were replicated using a version of the task in which baseline performance can be constrained. The usefulness of this approach is supported by the observation that tactile thresholds correlated with self-reported autistic traits in this non-clinical sample. We discuss the suitability of this adapted version of the CCT for measuring visual-tactile interactions in populations where unisensory tactile ability may differ within and between groups.

Investigating visual-tactile interactions over time and space in adults with autism.

It has been suggested that the sensory symptoms which affect many people with autism spectrum conditions (ASC) may be related to alterations in multisensory processing. Typically, the likelihood of interactions between the senses increases when information is temporally and spatially coincident. We explored visual-tactile interactions in adults with ASC for the first time in two experiments using low-level stimuli. Both participants with ASC and matched neurotypical controls only produced crossmodal interactions to near simultaneous stimuli, suggesting that temporal modulation is unaffected in the adult population. We also provide preliminary evidence that visual-tactile interactions may occur over greater spatial distances in participants with ASC, which merits further exploration.

Collinear facilitation and contour integration in autism: evidence for atypical visual integration.

Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized by impaired social interaction, atypical communication and a restricted repertoire of interests and activities. Altered sensory and perceptual experiences are also common, and a notable perceptual difference between individuals with ASD and controls is their superior performance in visual tasks where it may be beneficial to ignore global context. This superiority may be the result of atypical integrative processing. To explore this claim we investigated visual integration in adults with ASD (diagnosed with Asperger's Syndrome) using two psychophysical tasks thought to rely on integrative processing-collinear facilitation and contour integration. We measured collinear facilitation at different flanker orientation offsets and contour integration for both open and closed contours. Our results indicate that compared to matched controls, ASD participants show (i) reduced collinear facilitation, despite equivalent performance without flankers; and (ii) less benefit from closed contours in contour integration. These results indicate weaker visuospatial integration in adults with ASD and suggest that further studies using these types of paradigms would provide knowledge on how contextual processing is altered in ASD.