Plausibility judgement in schizophrenic patients: Evidence for a liberal acceptance bias

Previous work conducted with the probabilistic reasoning task has provided support for the claim that patients with delusional disorder and schizophrenia display a jumping to conclusions bias (early decisions on the basis of little evidence). Various explanations for this response pattern have been proposed. The goal of the present study was to provide further insight into the underlying mechanism(s) of this reasoning bias using a novel tasks for which competing accounts of the jumping to conclusions bias make opposing predictions. Twenty-nine schizophrenic patients and 28 healthy controls were administered pictures from the Thematic Apperception Task (TAT) and were asked to judge the plausibility of various interpretations for each picture. The results demonstrated that patients gave relatively high plausibility ratings for those interpretations that were judged as poor or unlikely by controls, but did not display abnormality on interpretations judged as good or excellent by controls. Contrary to a strict jumping to conclusions account, patients did not converge on one particular interpretation, but rather pursued multiple alternatives. Liberal acceptance is seen as a possible contributor to the emergence or maintenance of delusions: initial ambivalence may subsequently promote the acceptance of fallible interpretations.