Abnormal processing of irrelevant information in chronic schizophrenia: selective enhancement of Stroop facilitation.

Thirteen medication-free chronic schizophrenic patients and 11 normal control subjects were administered a trial by trial version of the Stroop Color Naming Task which evaluated separately the processes of interference and facilitation. There was no difference between the groups in the amount of interference to naming the colors of color-incongruent words. However, patients with schizophrenia showed significantly greater speed in naming the colors of color-congruent words when compared with control subjects. Thus, facilitation on the Stroop Task appears to be selectively enhanced in schizophrenia. Similar findings have been recently observed in patients with Parkinson's disease. This result may indicate a selective disruption of an automatic inhibitory process in this patient group and is consistent with the hypothesis that a deficit in mesocortical dopamine projections to the frontal cortex underlies some of the cognitive deficits of chronic schizophrenia.