Hypothesis testing in patients with persecutory delusions: comparison with depressed and normal subjects.

The hypothesis-testing skills of patients with persecutory delusions were studied, and compared with those of matched depressed and normal control groups. Subjects were required to complete a series of visual discrimination problems in which they had to choose between pairs of stimuli presented on cards. Following positive or negative feedback from the examiner, subjects' ability to progressively narrow down the set of possible correct solutions was assessed. The groups did not differ in the range or total number of hypotheses generated. The deluded subjects were less inclined than the controls to stick to their hypotheses when given positive feedback and were more inclined to stick to their hypotheses following negative feedback. They also showed less evidence of 'focusing' down their hypothesis to an overall correct solution, in response to successive feedback.