On each of a sequence of trials subjects had to guess whether a cross would appear on the left or the right side of a computer screen. The sequence of cross positions was random. Normal controls, manic-depressive patients and patients with senile dementia produced relatively random sequences of responses, as did acute schizophrenic patients with positive symptoms. Acute schizophrenic patients with negative symptoms and chronic patients produced more stereotyped sequences with many response alternations (LRLR). Chronic schizophrenic patients with negative symptoms and intellectual deterioration (defect state) produced very stereotyped sequences with many preservations (LLLL). This severe restriction of response sequences is similar to that shown by animals after treatment with amphetamine. It is suggested that it is due to an impairment of a higher order control process which normally inhibits the repetition of sequences of behaviour when these have proved inappropriate.
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