"Mental set" in controls, postalcoholics, chronic schizophrenics, and "organics"

Subjects consisted of (normal) controls, postalcoholics, chronic schizophrenics, and "organics" (a miscellaneous group of patients with acquired organic brain disorders including posttraumatic encephalopathy, Alzheimer's disease, Behçet's disease, Huntington's chorea and poststroke encephalopathy). "Mental set" was measured by comparisons of simple auditory-manual reaction times (RTs) at preparatory intervals (PIs) of 2, 5, and 10 sec following "warning" light flashes. First, the PIs were varied randomly over 48 trials (irregular procedure); then, each of the three PIs was held constant for 16 successive trials (regular procedure). Overall RTs increased significantly and progressively from controls to postalcoholics to chronic schizophrenics to organics. Mean differences between irregular and regular RTs at each PI were either significantly less for postalcoholics, chronic schizophrenics, as well as chronic schizophrenics and organics show distinct impairment of "mental set," which may be a sign of organic brain dysfunction, if other factors such as severe cultural deprivation can be excluded.