Objective: Abnormalities of attention are considered the fundamental deficits in cognitive function manifested by patients with schizophrenia. The authors administered variations of two types of cognitive tasks to patients with 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 results on a task in which subjects were to make a response if the word "nine" was 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 the word "press"). The building up of a prepotent response tendency was tested by manipulating the probability with which the cue and imperative stimulus 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 attributable to problems in the "motoric" component of response readiness was operationalized by having subjects perform a secondary motor task concurrent with the attentional task.
Results: Patients with schizophrenia performed significantly worse than the normal comparison subjects on all tasks. However, none of the four manipulations of the Continuous Performance Test tasks had a differential impact on the patients' performance speed or accuracy. In contrast, there was a significant interaction of group, delay interval, and target probability in which patients made disproportionately more omission errors at short delay intervals and at low target probabilities.
Conclusions: The findings may call into question the explanatory power of certain well-known contemporary mechanistic accounts of performance on the Continuous Performance Test in patients with schizophrenia. The findings suggest 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.