Taking others into account: combining directly experienced and indirect information in schizophrenia

An abnormality in inference, resulting in distorted internal models of the world, has been argued to be the common key to heterogeneous psychopathology in schizophrenia. However, findings have been mixed as to wherein the abnormality lies and have typically failed to find convincing relations to symptoms. The limited and inconsistent findings may have been due to methodological limitations of the experimental design, such as conflating other factors (e.g. comprehension) with the inferential process of interest, and a failure to adequately assess and model the key aspects of the inferential process. Here, we investigated probabilistic inference based on multiple sources of information using a new digital version of the beads task, framed in a social context. Thirty-five patients with schizophrenia or schizo-affective disorder with a wide range of symptoms and 40 matched healthy controls performed the task, where they guessed the color of the next marble drawn from an urn based on a sample from the urn as well the choices and expressed confidence of four people, each with their own independent sample (which was hidden from participant view). We relied on theoretically motivated computational models to assess which model best captured the inferential process and investigated whether it could serve as a mechanistic model for both psychotic and negative symptoms. We found that ‘circular inference’ best described the inference process, where patients over-weighed and over-counted direct experience and under-weighed information from others. Crucially, over-counting of direct experience was uniquely associated with most psychotic and negative symptoms. In addition, patients with worse social cognitive function had more difficulties using others’ confidence to inform their choices. This difficulty was related to worse real-world functioning. The findings could not be ascribed to differences of working memory, executive function, intelligence or antipsychotic medication. These results suggest hallucinations, delusions and negative symptoms could stem from the a common underlying abnormality in inference, where directly experienced information is assigned an unreasonable weight and taken into account multiple times. By this, even unreliable first hand experiences may gain disproportionate significance. The effect can lead to false perceptions (hallucinations), false beliefs (delusions) and deviant social behavior (e.g. loss of interest in others, bizarre and inappropriate behavior). This may be particularly problematic for patients with social cognitive deficits, as they may fail to make use of corrective information from others, ultimately leading to worse social functioning.