All or nothing belief updating in patients with schizophrenia reduces precision and flexibility of beliefs

Schizophrenia is characterized by abnormal perceptions and beliefs, but the computational mechanisms through which these abnormalities emerge remain unclear. One prominent hypothesis asserts that such abnormalities result from overly precise representations of prior knowledge, which in turn lead beliefs to become insensitive to feedback. In contrast, another prominent hypothesis asserts that such abnormalities result from a tendency to interpret prediction errors as indicating meaningful change, leading to the assignment of aberrant salience to noisy or misleading information. Here we examine behaviour of patients and control subjects in a behavioural paradigm capable of adjudicating between these competing hypotheses and characterizing belief updates directly on individual trials. We show that patients are more prone to completely ignoring new information and perseverating on previous responses, but when they do update, tend to do so completely. This updating strategy limits the integration of information over time, reducing both the flexibility and precision of beliefs and provides a potential explanation for how patients could simultaneously show over-sensitivity and under-sensitivity to feedback in different paradigms.