Bryan Paton

The Rubber Hand Illusion Reveals Proprioceptive and Sensorimotor Differences in Autism Spectrum Disorders.

Autism spectrum disorder (ASD) is characterised by differences in unimodal and multimodal sensory and proprioceptive processing, with complex biases towards local over global processing. Many of these elements are implicated in versions of the rubber hand illusion (RHI), which were therefore studied in high-functioning individuals with ASD and a typically developing control group. Both groups experienced the illusion. A number of differences were found, related to proprioception and sensorimotor processes. The ASD group showed reduced sensitivity to visuotactile-proprioceptive discrepancy but more accurate proprioception. This group also differed on acceleration in subsequent reach trials. Results are discussed in terms of weak top-down integration and precision-accuracy trade-offs. The RHI appears to be a useful tool for investigating multisensory processing in ASD.

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.

Dichoptic Viewing Methods for Binocular Rivalry Research: Prospects for Large-Scale Clinical and Genetic Studies

Binocular rivalry (BR) is an intriguing phenomenon that occurs when two different images are presented, one to each eye, resulting in alternation or rivalry between the percepts. The phenomenon has been studied for nearly 200 years, with renewed and intensive investigation over recent decades. The rate of perceptual switching has long been known to vary widely between individuals but to be relatively stable within individuals. A recent twin study demonstrated that individual variation in BR rate is under substantial genetic control, a finding that also represented the first report, using a large study, of genetic contribution for any post-retinal visual processing phenomenon. The twin study had been prompted by earlier work showing BR rate was slow in the heritable psychiatric condition, bipolar disorder (BD). Together, these studies suggested that slow BR may represent an endophenotype for BD, and heralded the advent of modern clinical and genetic studies of rivalry. This new focus has coincided with rapid advances in 3D display technology, but despite such progress, specific development of technology for rivalry research has been lacking. This review therefore compares different display methods for BR research across several factors, including viewing parameters, image quality, equipment cost, compatibility with other investigative methods, subject group, and sample size, with a focus on requirements specific to large-scale clinical and genetic studies. It is intended to be a resource for investigators new to BR research, such as clinicians and geneticists, and to stimulate the development of 3D display technology for advancing interdisciplinary studies of rivalry.

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.

Attenuated self-tickle sensation even under trajectory perturbation

The efference copy account of the tickle effect (i.e., our inability to tickle ourselves) predicts no tickle effect (i.e., an ability to tickle ourselves) when the trajectory of a tactile stimulus is perturbed relative to the associated movement, and there is evidence in support of this. The active inference account, however, predicts the tickle effect should survive trajectory perturbation. We test these accounts of the tickle effect under the hypothesis that previous findings are due to attentional modulation, and that the tickle effect will be found in a paradigm with no conscious attention directed to the trajectory perturbation. We thus expected to find support for active inference. Our first experiment confirms this hypothesis, while our second seeks to explain previous findings in terms of the modulation of the tickle sensation when there is awareness of, and different degrees of attention to, the spatial tactile and kinesthetic trajectories.

No Relationship Between Binocular Rivalry Rate and Eye-Movement Profiles in Healthy Individuals: A Bayes Factor Analysis

Binocular rivalry (BR) is an intriguing phenomenon in which conflicting images are presented, one to each eye, resulting in perceptual alternations between each image. The rate of BR has been proposed as a potential endophenotype for bipolar disorder because (a) it is well established that this highly heritable psychiatric condition is associated with slower BR rate than in controls, and (b) an individual’s BR rate is approximately 50% genetically determined. However, eye movements (EMs) could potentially account for the slow BR trait given EM anomalies are observed in psychiatric populations, and there has been report of an association between saccadic rate and BR rate in healthy individuals. Here, we sought to assess the relationship between BR rate and EMs in healthy individuals (N = 40, mean age = 34.4) using separate BR and EM tasks, with the latter measuring saccades during anticipatory, antisaccade, prosaccade, self-paced, free-viewing, and smooth-pursuit tasks. No correlation was found between BR rate and any EM measure for any BR task (p > .01) with substantial evidence favoring this lack of association (BF01 > 3). This finding is in contrast to previous data and has important implications for using BR rate as an endophenotype. If replicated in clinical psychiatric populations, EM interpretations of the slow BR trait can be excluded.

Skull-bound perception and precision optimization through culture

Clark acknowledges but resists the indirect mind-world relation inherent in prediction error minimization (PEM). But directness should also be resisted. This creates a puzzle, which calls for reconceptualization of the relation. We suggest that a causal conception captures both aspects. With this conception, aspects of situated cognition, social interaction and culture can be understood as emerging through precision optimization.

Time as context: The influence of hierarchical patterning on sensory inference

Time, or more specifically temporal structure, is a critical variable in understanding how the auditory system uses acoustic patterns to predict input, and to filter events based on their relevance. A key index of this filtering process is the auditory evoked potential component known as mismatch negativity or MMN. In this paper we review findings of smaller MMN in schizophrenia through the lens of time as an influential contextual variable. More specifically, we review studies that show how MMN to a locally rare pattern-deviation is modulated by the longer-term context in which it occurs. Empirical data is presented from a non-clinical sample confirming that the absence of a stable higher-order structure to sound sequences alters the way MMN amplitude changes over time. This result is discussed in relation to how hierarchical pattern learning might enrich our understanding of how and why MMN amplitude modulation is disrupted in schizophrenia.

Transdiagnostic variations in impulsivity and compulsivity in obsessive-compulsive disorder and gambling disorder correlate with effective connectivity in cortical-striatal-thalamic-cortical circuits.

Background Individual differences in impulsivity and compulsivity is thought to underlie vulnerability to a broad range of disorders and are closely tied to cortical-striatal-thalamic-cortical (CSTC) function. However, whether impulsivity and compulsivity in clinical disorders is continuous with the healthy population and explains CSTC dysfunction across different disorders remains unclear. Methods We characterized the relationship between CSTC effective connectivity, estimated using dynamic causal modelling of functional magnetic resonance imaging data, and dimensional phenotypes of impulsivity and compulsivity in two symptomatically distinct but phenotypically related disorders, obsessive-compulsive disorder (OCD) and gambling disorder (GD). 487 online participants provided data for modelling of dimensional phenotypes. These data were combined with 34 OCD patients, 22 GD patients, and 39 healthy controls, who underwent functional magnetic resonance imaging. Results Three core dimensions were identified: disinhibition, impulsivity, and compulsivity. Patients’ scores on these dimensions were continuously distributed with the healthy participants, supporting a continuum model of psychopathology. Across all participants, higher disinhibition correlated with lower bottom-up connectivity in the dorsal circuit and increased bottom-up connectivity in the ventral circuit, and higher compulsivity correlated with reduced bottom-up connectivity in the dorsal circuit. Similar changes in effective connectivity were observed with increasing clinical severity that were not accounted for by phenotypic variation, demonstrating convergence towards behaviourally and clinically relevant changes in brain dynamics. Effective connectivity did not differ as a function of traditional diagnostic labels. Conclusions CSTC dysfunction across OCD and GD is better characterized by dimensional phenotypes than diagnostic comparisons, supporting investigation of quantitative liability phenotypes.