Altered Semantic Prediction Error Processing with Increasing Schizotypal and Autistic Traits

Predictive processing has been proposed as an explanatory framework for symptom development in both autism (ASD) and schizophrenia (SSD) spectrum disorders, with ASD being associated with an overweighting of (low-level) sensory evidence whereas SSD is characterized by an overweighting of (high-level) prior beliefs. The goal of the present study was to investigate these hypotheses in subclinical expressions of ASD and SSD in the domain of language processing. To test this, we used an auditory comprehension task designed to directly manipulate the precision of high-level semantic prior beliefs and low-level sensory evidence. We applied hierarchical Bayesian belief updating modeling to quantify this effect and used EEG to examine whether an imbalance in the weighting of prior beliefs and sensory evidence would be characterized by altered processing of semantic precision-weighted prediction errors as indexed by alterations in mean N400 amplitudes. Computational modeling revealed that increasing schizotypal traits were associated with a significant overweighting of prior beliefs, while autistic traits did not show a significant shift. Linear mixed models on the mean N400 amplitudes further indicated that this schizotypy-related overweighting of semantic prior beliefs was reflected in a reduced semantic prediction error signal, indexed by smaller N400 differences between low entropy sentences and both high and low-mismatch sentences. A similar pattern emerged for increasing autistic traits, though the effect was weaker and less distinct, pointing to a subtle overweighting of semantic prior beliefs, only. Overall, our findings provide converging computational and electrophysiological support for an overweighting of semantic prior beliefs with increasing subclinical schizotypy, consistent with predictive processing accounts of SSD, whereas we did not find evidence for an overweighting of sensory evidence with increasing autistic traits, with electrophysiological results instead pointing toward subtle alterations in the weighting of semantic prior beliefs.