Perceptual Bayesian inference in autism and schizophrenia

Recent theories in the field of computational psychiatry regard schizophrenia (SCZ) and autistic spectrum disorders (ASD) as impairments in Bayesian inference performed by the brain. In Bayesian terms, perception is a result of optimal real-time integration of sensory information (’likelihood’), which is intrinsically noisy and ambiguous, and prior expectations about the states of the world (‘prior’), which serve to disambiguate the meaning of the sensory information. Priors capture statistical regularities in the environment and are constantly updated to keep up with any changes in these regularities. The extent to which prior or likelihood dominate perception depends on the uncertainty with which they are represented, with less uncertainty resulting in more influence. Individuals with ASD and SCZ might show impairments in how they update their priors and/or how much uncertainty there is ascribed to prior and likelihood representations, leading to differences in inference. While this Bayesian account can be argued to be consistent with many previous experimental findings and symptoms of SCZ and ASD, recent experimental work inspired by these ideas has produced mixed results. In this work, we investigated possible Bayesian impairments in SCZ and ASD experimentally by addressing some of the methodological limitations of the previous work. Most notably, we used an experimental design that allows to disentangle and quantify separate influences of priors and likelihoods, and we tested both SCZ and ASD patient groups as well as autistic and schizotypy traits in the general population. We administered a visual motion perception task that rapidly induces prior expectations about the stimulus motion direction, leading to biases and occasional hallucinations that can be well described by a Bayesian model. In this task, autistic traits were found to be associated with reduced biases, which was underlied by more precise sensory representations, while the acquired priors were not affected by autistic traits. Patients with ASD, however, showed no evidence of increased sensory precision, while there also were no impairments in the acquisition of priors. We also found no effects in the acquisition of priors or sensory representations along schizotypy traits and in patients with SCZ. However, under conditions of high ambiguity SCZ patients were less likely to hallucinate the stimulus than controls. The second part of the thesis is focused on further exploratory analyses conducted using these same datasets. First, we investigated post-perceptual repulsion effects in our task and whether they were related to trait or group differences. We found clear evidence of repulsion from the cardinal directions. In addition to that, we found evidence for a repulsion from the central reference angle, which was randomly selected for each participant and which could only be inferred from the stimulus statistics. Furthermore, we found the repulsion from the central reference angle to be reduced along schizotypy traits. Interestingly, in both SCZ and ASD groups this repulsion was also found to be negligible. While these results are exploratory, they might point to a trans-diagnostic features of ASD and SCZ. Second, we investigated within-trial dynamics of evidence accumulation by constructing a Continuous Choice Drift Diffusion Model (CDM) – an extension of the classical binary choice drift diffusion model. The results of this model showed that increased sensory precision along AQ found in a Bayesian model was underlied by faster drift rates, while slower responses and reduced hallucinations in SCZ were explained by a larger decision threshold. In addition, this model provided a more complete characterization of the performance in this task (by including reaction times) and it serves to emphasize the importance of accounting for exposure to stimulus duration and judgement time in future studies investigating Bayesian inference. Together, this work provides novel experimental evidence that speaks to the hypothesis of impaired Bayesian inference in ASD and SCZ. Furthermore, the analysis of reference repulsion effects and within-trial dynamics provide additional insight related to SCZ and ASD differences that extend beyond the Bayesian framework

Visual statistical learning and integration of perceptual priors are intact in attention deficit hyperactivity disorder

BackgroundDeficits in visual statistical learning and predictive processing could in principle explain the key characteristics of inattention and distractibility in attention deficit hyperactivity disorder (ADHD). Specifically, from a Bayesian perspective, ADHD may be associated with flatter likelihoods (increased sensory processing noise), and/or difficulties in generating or using predictions. To our knowledge, such hypotheses have never been directly tested.MethodsWe here test these hypotheses by evaluating whether adults diagnosed with ADHD (n = 17) differed from a control group (n = 30) in implicitly learning and using low-level perceptual priors to guide sensory processing. We used a visual statistical learning task in which participants had to estimate the direction of a cloud of coherently moving dots. Unbeknown to the participants, two of the directions were more frequently presented than the others, creating an implicit bias (prior) towards those directions. This task had previously revealed differences in other neurodevelopmental disorders, such as autistic spectrum disorder and schizophrenia.ResultsWe found that both groups acquired the prior expectation for the most frequent directions and that these expectations substantially influenced task performance. Overall, there were no group differences in how much the priors influenced performance. However, subtle group differences were found in the influence of the prior over time.ConclusionOur findings suggest that the symptoms of inattention and hyperactivity in ADHD do not stem from broad difficulties in developing and/or using low-level perceptual priors

Acquisition of visual priors and induced hallucinations in chronic schizophrenia

Prominent theories suggest that symptoms of schizophrenia stem from learning deficiencies resulting in distorted internal models of the world. To test these theories further, we used a visual statistical learning task known to induce rapid implicit learning of the stimulus statistics. In this task, participants are presented with a field of coherently moving dots and are asked to report the presented direction of the dots (estimation task), and whether they saw any dots or not (detection task). Two of the directions were more frequently presented than the others. In controls, the implicit acquisition of the stimuli statistics influences their perception in two ways: (i) motion directions are perceived as being more similar to the most frequently presented directions than they really are (estimation biases); and (ii) in the absence of stimuli, participants sometimes report perceiving the most frequently presented directions (a form of hallucinations). Such behaviour is consistent with probabilistic inference, i.e. combining learnt perceptual priors with sensory evidence. We investigated whether patients with chronic, stable, treated schizophrenia (n = 20) differ from controls (n = 23) in the acquisition of the perceptual priors and/or their influence on perception. We found that although patients were slower than controls, they showed comparable acquisition of perceptual priors, approximating the stimulus statistics. This suggests that patients have no statistical learning deficits in our task. This may reflect our patients’ relative wellbeing on antipsychotic medication. Intriguingly, however, patients experienced significantly fewer (P = 0.016) hallucinations of the most frequently presented directions than controls when the stimulus was absent or when it was very weak (prior-based lapse estimations). This suggests that prior expectations had less influence on patients’ perception than on controls when stimuli were absent or below perceptual threshold

The Influence of Feedback on Task-Switching Performance:A Drift Diffusion Modeling Account

Task-switching is an important cognitive skill that facilitates our ability to choose appropriate behavior in a varied and changing environment. Task-switching training studies have sought to improve this ability by practicing switching between multiple tasks. However, an efficacious training paradigm has been difficult to develop in part due to findings that small differences in task parameters influence switching behavior in a non-trivial manner. Here, for the first time we employ the Drift Diffusion Model (DDM) to understand the influence of feedback on task-switching and investigate how drift diffusion parameters change over the course of task switch training. We trained 316 participants on a simple task where they alternated sorting stimuli by color or by shape. Feedback differed in six different ways between subjects groups, ranging from No Feedback (NFB) to a variety of manipulations addressing trial-wise vs. Block Feedback (BFB), rewards vs. punishments, payment bonuses and different payouts depending upon the trial type (switch/non-switch). While overall performance was found to be affected by feedback, no effect of feedback was found on task-switching learning. Drift Diffusion Modeling revealed that the reductions in reaction time (RT) switch cost over the course of training were driven by a continually decreasing decision boundary. Furthermore, feedback effects on RT switch cost were also driven by differences in decision boundary, but not in drift rate. These results reveal that participants systematically modified their task-switching performance without yielding an overall gain in performance

Individual Differences in Computational Psychiatry: A Review of Current Challenges

Bringing precision to the understanding and treatment of mental disorders requires instruments for studying clinically relevant individual differences. One promising approach is the development of computational assays: integrating computational models with cognitive tasks to infer latent patient-specific disease processes in brain computations. While recent years have seen many methodological advancements in computational modelling and many cross-sectional patient studies, much less attention has been paid to basic psychometric properties (reliability and construct validity) of the computational measures provided by the assays. In this review, we assess the extent of this issue by examining emerging empirical evidence. To contextualize this, we also provide a more general perspective on key developments that are needed for translating computational assays to clinical practice. Emerging evidence suggests that most computational measures show poor-to-moderate reliability and often provide little improvement over simple behavioral measures. Furthermore, behavioral and computational measures used to test computational accounts of mental disorders show a lack of convergent validity, which compromises their interpretability. Taken together, these issues pose a risk of invalidating previous findings and undermining ongoing research efforts using computational assays to study individual (and even group) differences. We suggest that cross-sectional single-task designs, which currently dominate the research landscape, are partly to blame for these problems and therefore are not suitable for solving them. Instead, reliability and construct validity need to be studied more systematically using longitudinal designs with batteries of tasks. Finally, to enable clinical applications, it will be necessary to establish predictive and longitudinal validity, and to make the assays more efficient and less burdensome

Autistic traits, but not schizotypy, predict increased weighting of sensory information in Bayesian visual integration.

Recent theories propose that schizophrenia/schizotypy and autistic spectrum disorder are related to impairments in Bayesian inference that is, how the brain integrates sensory information (likelihoods) with prior knowledge. However existing accounts fail to clarify: (i) how proposed theories differ in accounts of ASD vs. schizophrenia and (ii) whether the impairments result from weaker priors or enhanced likelihoods. Here, we directly address these issues by characterizing how 91 healthy participants, scored for autistic and schizotypal traits, implicitly learned and combined priors with sensory information. This was accomplished through a visual statistical learning paradigm designed to quantitatively assess variations in individuals' likelihoods and priors. The acquisition of the priors was found to be intact along both traits spectra. However, autistic traits were associated with more veridical perception and weaker influence of expectations. Bayesian modeling revealed that this was due, not to weaker prior expectations, but to more precise sensory representations

The Influence of Feedback on Task-Switching Performance: A Drift Diffusion Modeling Account.

Task-switching is an important cognitive skill that facilitates our ability to choose appropriate behavior in a varied and changing environment. Task-switching training studies have sought to improve this ability by practicing switching between multiple tasks. However, an efficacious training paradigm has been difficult to develop in part due to findings that small differences in task parameters influence switching behavior in a non-trivial manner. Here, for the first time we employ the Drift Diffusion Model (DDM) to understand the influence of feedback on task-switching and investigate how drift diffusion parameters change over the course of task switch training. We trained 316 participants on a simple task where they alternated sorting stimuli by color or by shape. Feedback differed in six different ways between subjects groups, ranging from No Feedback (NFB) to a variety of manipulations addressing trial-wise vs. Block Feedback (BFB), rewards vs. punishments, payment bonuses and different payouts depending upon the trial type (switch/non-switch). While overall performance was found to be affected by feedback, no effect of feedback was found on task-switching learning. Drift Diffusion Modeling revealed that the reductions in reaction time (RT) switch cost over the course of training were driven by a continually decreasing decision boundary. Furthermore, feedback effects on RT switch cost were also driven by differences in decision boundary, but not in drift rate. These results reveal that participants systematically modified their task-switching performance without yielding an overall gain in performance

Test-retest reliability of behavioral and computational measures of advice taking under volatility

The development of computational models for studying mental disorders is on the rise. However, their psychometric properties remain understudied, posing a risk to undermine their use in empirical research and clinical translation. Here we investigated test-retest reliability (with a 2-week interval) of a computational assay probing advice-taking under volatility with a Hierarchical Gaussian Filter (HGF) model. In a sample of 39 healthy participants, we found the computational measures to have largely poor reliability (intra-class correlation coefficient or ICC < 0.5), on par with the behavioral measures of task performance. Further analysis revealed that reliability was substantially impacted by intrinsic measurement noise (indicated by parameter recovery analysis) and to a smaller extent by practice effects. However, a large portion of within-subject variance remained unexplained and may be attributable to state-like fluctuations. Despite the poor test-retest reliability, we found the assay to have face validity at the group level. Overall, our work highlights that the different sources of variance affecting test-retest reliability need to be studied in greater detail. A better understanding of these sources would facilitate the design of more psychometrically sound assays, which would improve the quality of future research and increase the probability of clinical translation

Altered Perception of Environmental Volatility During Social Learning in Emerging Psychosis

Paranoid delusions or unfounded beliefs that others intend to deliberately cause harm are a frequent and burdensome symptom in early psychosis, but their emergence and consolidation still remains opaque. Recent theories suggest that overly precise prediction errors lead to an unstable model of the world providing a breeding ground for delusions. Here, we employ a Bayesian approach to test for such an unstable model of the world and investigate the computational mechanisms underlying emerging paranoia. We modelled behaviour of 18 first-episode psychosis patients (FEP), 19 individuals at clinical high risk for psychosis (CHR-P), and 19 healthy controls (HC) during an advice-taking task designed to probe learning about others’ changing intentions. We formulated competing hypotheses comparing the standard Hierarchical Gaussian Filter (HGF), a Bayesian belief updating scheme, with a mean-reverting HGF to model an altered perception of volatility. There was a significant group-by-volatility interaction on advice-taking suggesting that CHR-P and FEP displayed reduced adaptability to environmental volatility. Model comparison favored the standard HGF in HC, but the mean-reverting HGF in CHR-P and FEP in line with perceiving increased volatility, although model attributions in CHR-P were heterogeneous. We observed correlations between perceiving increased volatility and positive symptoms generally as well as with frequency of paranoid delusions specifically. Our results suggest that FEP are characterised by a different computational mechanism – perceiving the environment as increasingly volatile – in line with Bayesian accounts of psychosis. This approach may prove useful to investigate heterogeneity in CHR-P and identify vulnerability for transition to psychosis