Atypical perception: cognitive, behavioural, and neural correlates

Our phenomenological experience of our shared physical world can vary drastically across individuals. Subjective sensory sensitivity constitutes one test-case of this type of variability, as the same simple sensory stimulation can lead to responses ranging from fascination to neutrality to outright aversion in different people. These differences can be found in the general population yet are markedly more prominent in association with neurological and developmental conditions and disorders, including migraine, ADHD, synaesthesia and autism spectrum disorders (ASD). The existing research on subjective sensory sensitivity has been conducted primarily within the field of developmental disorders, and particularly of ASD, where it has furthermore informed wide-ranging theories of its aetiology. The overarching aim of this thesis was to investigate potential underlying mechanisms of individual differences in atypical sensory experiences, focusing on subjective sensory sensitivity in the general population. While taking an individual differences approach, it is grounded primarily in the autism literature, aiming to dissociate the specific dimension of subjective sensory sensitivity from the broader autistic(-like) phenotype. Chapter 2 focused on the internal noise theory of ASD, according to which there are increased fluctuations in neural responses in ASD, leading to more variable percepts and behavioural responses. It aimed to replicate a previously reported correlation between autistic-like traits and response consistency using a psychophysical double-pass paradigm in the general population and investigate the role of subjective sensory sensitivity in this association. While we found that individual differences in response consistency are reliable across time, we did not detect any correlation between these and autistic-like traits. Chapter 3 investigated variability in macroscale cortical organization associated with autistic-like traits including subjective sensory sensitivity in the general population. Applying a dimensionality reduction technique to a resting-state fMRI dataset, components termed cortical gradients were derived. The principal component spanning from visual to default mode networks, is reliably conserved and is thought to reflect the transition from perception to abstract cognition. Individuals with higher subjective sensory sensitivity, yet not other autistic-like traits, show greater distance between the two poles of this principal gradient, indicating reduced functional integration. Chapters 4 and 5 investigated individual differences in perceptual inference supporting associative learning correlated with synaesthesia and autistic-like traits. The paradigm is designed to induce perceptual false alarms by repeatedly pairing a cue with a conditioned stimulus. The rate of these false alarms together with the results of a computational model of the underlying inference processes have previously shown imbalances in sensory evidence and prior knowledge in individuals prone to hallucinations in their daily lives. Synaesthetes show increased and fixed expectancies of the cue-stimulus association, while individuals with high levels of autistic-like traits show an increased learning rate in updating their belief in the cue-stimulus association. Findings of reduced reliance on prior knowledge in ASD, putatively leading to atypical sensory processing, may stem from a failure to learn and exploit the statistical regularities in the environment. Chapter 6 investigated individual differences and underlying mechanisms of choice history biases and their adaptation to sequential regularities. This showed evidence of reduced adaptation in choice history biases in people with particularly high levels of autistic-like traits. The underlying mechanisms were investigated by capitalizing on noise-driven fluctuations in the orientation statistics of the stimuli in a reverse-correlation analysis. This shows primarily increased stimulus-independent bias to respond in line with the predicted orientation though also changes in stimulus-dependent sensitivity to favour information consistent with the prediction. History bias adaptation measures derived from this analysis reveal a different pattern of results associated with high subjective sensory sensitivity compared to high levels of autistic-like traits. Together, these findings further characterize individual differences in perceptual decision-making and integration in individuals with atypical sensory experiences. More generally, they indicate that different types and aspects of atypical sensory experience constitute distinct and dissociable traits, underpinned by partially independent substrates beyond those associated with a broader cognitive profile.