Colin J. Palmer

Movement under uncertainty: the effects of the rubber-hand illusion vary along the nonclinical autism spectrum.

Recent research has begun to investigate sensory processing in relation to nonclinical variation in traits associated with the autism spectrum disorders (ASD). We propose that existing accounts of autistic perception can be augmented by considering a role for individual differences in top-down expectations for the precision of sensory input, related to the processing of state-dependent levels of uncertainty. We therefore examined ASD-like traits in relation to the rubber-hand illusion: an experimental paradigm that typically elicits crossmodal integration of visual, tactile, and proprioceptive information in an unusual illusory context. Individuals with higher ASD-like traits showed reduced effects of the rubber-hand illusion on perceived arm position and reach-to-grasp movements, compared to individuals with lower ASD-like traits. These differences occurred despite both groups reporting the typical subjective experience of the illusion concerning visuotactile integration and ownership for the rubber hand. Together these results suggest that the integration of proprioceptive information with cues for arm position derived from the illusory context differs between individuals partly in relation to traits associated with ASD. We suggest that the observed differences in sensory integration can be best explained in terms of differing expectations regarding the precision of sensory estimates in contexts that suggest uncertainty.

Context sensitivity in action decreases along the autism spectrum: a predictive processing perspective

Recent predictive processing accounts of perception and action point towards a key challenge for the nervous system in dynamically optimizing the balance between incoming sensory information and existing expectations regarding the state of the environment. Here, we report differences in the influence of the preceding sensory context on motor function, varying with respect to both clinical and subclinical features of autism spectrum disorder (ASD). Reach-to-grasp movements were recorded subsequent to an inactive period in which illusory ownership of a prosthetic limb was induced. We analysed the sub-components of reach trajectories derived using a minimum-jerk fitting procedure. Non-clinical adults low in autistic features showed disrupted movement execution following the illusion compared to a control condition. By contrast, individuals higher in autistic features (both those with ASD and non-clinical individuals high in autistic traits) showed reduced sensitivity to the presence of the illusion in their reaching movements while still exhibiting the typical perceptual effects of the illusion. Clinical individuals were distinct from non-clinical individuals scoring high in autistic features, however, in the early stages of movement. These results suggest that the influence of high-level representations of the environment differs between individuals, contributing to clinical and subclinical differences in motor performance that manifest in a contextual manner. As high-level representations of context help to explain fluctuations in sensory input over relatively longer time scales, more circumscribed sensitivity to prior or contextual information in autistic sensory processing could contribute more generally to reduced social comprehension, sensory impairments and a stronger desire for predictability and routine.

Bayesian Approaches to Autism: Towards Volatility, Action, and Behavior

Autism spectrum disorder currently lacks an explanation that bridges cognitive, computational, and neural domains. In the past 5 years, progress has been sought in this area by drawing on Bayesian probability theory to describe both social and nonsocial aspects of autism in terms of systematic differences in the processing of sensory information in the brain. The present article begins by synthesizing the existing literature in this regard, including an introduction to the topic for unfamiliar readers. The key proposal is that autism is characterized by a greater weighting of sensory information in updating probabilistic representations of the environment. Here, we unpack further how the hierarchical setting of Bayesian inference in the brain (i.e., predictive processing) adds significant depth to this approach. In particular, autism may relate to finer mechanisms involved in the context-sensitive adjustment of sensory weightings, such as in how neural representations of environmental volatility inform perception. Crucially, in light of recent sensorimotor treatments of predictive processing (i.e., active inference), hypotheses regarding atypical sensory weighting in autism have direct implications for the regulation of action and behavior. Given that core features of autism relate to how the individual interacts with and samples the world around them (e.g., reduced social responding, repetitive behaviors, motor impairments, and atypical visual sampling), the extension of Bayesian theories of autism to action will be critical for yielding insights into this condition.

Social Cognition as Causal Inference: Implications for Common Knowledge and Autism

This chapter explores the idea that the need to establish common knowledge is one feature that makes social cognition stand apart in important ways from cognition in general. We develop this idea on the background of the claim that social cognition is nothing but a type of causal inference. We focus on autism spectrum disorder (ASD) as our test case and propose that a specific type of problem with common knowledge processing is implicated in challenges to social cognition in this condition. This problem has to do with the individual’s assessment of the reliability of messages that are passed between people as common knowledge emerges. The proposal is developed on the background of our own empirical studies and outlines different ways common knowledge might be comprised. We discuss what these issues may tell us about ASD, about the relation between social and nonsocial cognition, about social objects, and about the dynamics of social networks.

Parkinson's disease alters multisensory perception: Insights from the Rubber Hand Illusion

Background: Manipulation of multisensory integration induces illusory perceptions of body ownership. Patients with Parkinsons disease (PD), a neurodegenerative disorder characterised by striatal dopamine deficiency, are prone to illusions and hallucinations and have sensory deficits. Dopaminergic treatment also aggravates hallucinations in PD. Whether multisensory integration in body ownership is altered by PD is unexplored. Objective: To study the effect of dopamine neurotransmission on illusory perceptions of body ownership. Methods: We studied the Rubber Hand Illusion (RHI) in 21 PD patients (on‐ and off‐medication) and 21 controls. In this experimental paradigm, synchronous stroking of a rubber hand and the subjects hidden real hand results in the illusory experience of ‘feeling’ the rubber hand, and proprioceptive mislocalisation of the real hand towards the rubber hand (‘proprioceptive drift’). Asynchronous stroking typically attenuates the RHI. Results: The effect of PD on illusory experience depended on the stroking condition (b = −2.15, 95% CI [−3.06, −1.25], p < .0001): patients scored questionnaire items eliciting the RHI experience higher than controls in the illusion‐attenuating (asynchronous) condition, but not in the illusion‐promoting (synchronous) condition. PD, independent of stroking condition, predicted greater proprioceptive drift (b = 15.05, 95% CI [6.05, 24.05], p = .0022); the longer the disease duration, the greater the proprioceptive drift. However, the RHI did not affect subsequent reaching actions. On‐medication patients scored both illusion (critical) and mock (control) questionnaire items higher than when off‐medication, an effect that increased with disease severity (log (OR) =.014, 95% CI [.01, .02], p < .0001). Conclusion: PD affects illusory perceptions of body ownership in situations that do not typically induce them, implicating dopamine deficit and consequent alterations in cortico‐basal ganglia‐thalamic circuitry in multisensory integration. Dopaminergic treatment appears to increase suggestibility generally rather than having a specific effect on own‐body illusions, a novel finding with clinical and research implications. HighlightsParkinsons disease affects own‐body perception in the Rubber Hand Illusion (RHI).Patients do not reject RHI as strongly as controls after asynchronous stroking.RHI strength is similar between patients and controls after synchronous stroking.Parkinsons disease increases proprioceptive drift independent of stroking.Dopaminergic drugs increased agreement with questionnaire items non‐discriminately.

Biases in perceiving gaze vergence.

The focus of another person’s gaze is an important cue in social interactions, helping us to understand others’ intentions, predict their behavior, and allocate our own attention appropriately. The perception of gaze vergence provides information about the distance at which another person is fixating, but has yet to receive much empirical attention. Here, we report that observers display systematic biases when perceiving others’ gaze vergence and depth of fixation. Specifically, they perceive others as having convergent gaze and fixating at closer distances, especially when gaze is directed downward or observed under conditions of sensory uncertainty. These biases may reflect the predominance of convergent over divergent gaze in everyday social interactions and implicit knowledge of the physical structure of the environment, in which objects below our line of sight are typically closer. These findings demonstrate the sophistication of social vision, in which our visual perception of others is shaped by statistical regularities, and help to establish the perception of others’ gaze vergence and fixation distance as a subject of psychological investigation.

Deep Brain Stimulation for Parkinson’s disease changes perception in the Rubber Hand Illusion

Parkinson’s disease (PD) alters cortico-basal ganglia-thalamic circuitry and susceptibility to an illusion of bodily awareness, the Rubber Hand Illusion (RHI). Bodily awareness is thought to result from multisensory integration in a predominantly cortical network; the role of subcortical connections is unknown. We studied the effect of modulating cortico-subcortical circuitry on multisensory integration for bodily awareness in 24 PD patients treated with subthalamic nucleus (STN) deep brain stimulation (DBS), in comparison to 21 healthy volunteers, using the RHI experiment. Typically, synchronous visuo-tactile cues induce a false perception of touch on the rubber hand as if it were the subject’s hand, whereas asynchronous visuo-tactile cues do not. However, we found that in the asynchronous condition, patients in the off-stimulation state did not reject the RHI as strongly as healthy controls; patients’ rejection of the RHI strengthened when STN-DBS was switched on, although it remained weaker than that of controls. Patients in the off-stimulation state also misjudged the position of their hand, indicating it to be closer to the rubber hand than controls. However, STN-DBS did not affect proprioceptive judgements or subsequent arm movements altered by the perceptual effects of the illusion. Our findings support the idea that the STN and subcortical connections have a key role in multisensory integration for bodily awareness. Decision-making in multisensory bodily illusions is discussed.

Retraction Notice to: Vergence eye movements direct others’ attention in three-dimensional space

(Current Biology 28, R545–R546; May 7, 2018) In our Correspondence, we reported that the spatial focus of visual attention can be cued by another’s vergence eye movements. However, we subsequently discovered that there was a mistake in the analysis such that reaction time data were systematically mislabeled. When we reran the analysis on the correctly labeled data, the reported cueing effect no longer reached statistical significance. We are therefore retracting our paper and apologize to the scientific community for any inconvenience caused.