Continuous performance test and schizophrenia: A test of stimulus-responsecompatibility, working memory, response readiness, or none of the above?

Objective: Abnormalities of attention are considered the fundamental defici ts in cognitive function manifested by patients with schizophrenia. The aut hors administered variations of two types of cognitive tasks to patients wi th schizophrenia (N=20) and normal comparison subjects (N=30) to test four possible cognitive mechanisms that might account for such abnormalities. Method: Variations of the Continuous Performance Test were used to test the four mechanisms. Stimulus-response mapping was explored by comparing resul ts on a task in which subjects were to make a response if the word "nine" w as preceded by the word "one" with results on a task in which the required response was made explicit by the stimulus (the word "ready" followed by th e word "press"). The building up of a prepotent response tendency was teste d by manipulating the probability with which the cue and imperative stimulu s appeared (17% or 50%). The amount of working memory required to maintain contextual information was tested by using different delay intervals (1000 msec and 3000 msec). The extent to which problems in vigilance might be att ributable to problems in the "motoric" component of response readiness was operationalized by having subjects perform a secondary motor task concurren t with the attentional task. Results: Patients with schizophrenia performed significantly worse than the normal comparison subjects on all tasks. However, none of the four manipul ations of the Continuous Performance Test tasks had a differential impact o n the patients' performance speed or accuracy. In contrast, there was a sig nificant interaction of group, delay interval, and target probability in wh ich patients made disproportionately more omission errors at short delay in tervals and at low target probabilities. Conclusions: The findings may call into question the explanatory power of c ertain well-known contemporary mechanistic accounts of performance on the C ontinuous Performance Test in patients with schizophrenia. The findings sug gest that a difficulty in rapidly encoding information (i.e., constructing a representation) in certain "unengaging" situations may be at the core of deficits on tasks associated with this attentional test.