Jumping to delusions in early psychosis.

Introduction: Patients with delusions typically seek less information when making decisions than controls ("jumping-to-conclusions", JTC) and paradoxically over-adjust to counter-evidence on probabilistic reasoning tasks. Previous studies have examined JTC bias across the delusion-prone continuum, but have not considered the co-occurrence of both biases at early stages of psychosis. This was our aim.

Method: Twenty-three early psychosis patients and 19 healthy controls completed two versions of the probabilistic reasoning task: a "draws-to-decision" version (to assess JTC) and a "graded-estimates" version (to assess over-adjustment). Both versions have been used previously with clinically delusional people with schizophrenia. IQ, memory and executive function were also examined.

Results: Patients took fewer trials to reach a decision in the draws-to-decision version and showed greater over-adjustment to counter-evidence in the graded-estimates version than controls. Across groups, those who jumped to conclusions showed greater over-adjustment. Poor executive function predicted more extreme biases in controls but not in patients. Task performances were unrelated to memory. Similar results were evident in patient and control subgroups matched on IQ, and years of formal education.

Conclusions: A jumping-to-conclusions bias and an over-adjustment bias co-occurred in the early psychosis patients. Implications are discussed concerning the role of such biases in delusion-proneness.