The performance of schizophrenic and depressed subjects on tests of fluency: Support for a compromise in dorsolateral prefrontal functioning

Fifty-seven subjects (21 schizophrenia, 13 depressed, and 23 normal) matched for NART Verbal IQ were compared on two fluency tests (the Verbal Fluency Test and the Design Fluency Test) and on the modified Wisconsin Card Sorting Test. Both the clinical groups performed significantly below the normals on measures of production on the fluency tests, but not on measures of error. This finding is consistent with the notion proposed by Crowe (1992) that both clinical groups feature compromise in the dorsolateral prefrontal cortex (DLPFC) bilaterally but not of the orbital prefrontal area. The two clinical groups performed consistently across the tests employed, with the single exception that the schizophrenic subjects tended to produce more perseverative and nonperseverative errors than did the depressed subjects. A comparison of the performance of the subjects across the time-slices of the fluency tests revealed that the performance on the verbal fluency tests decreased from each time-slice to the next, while on the design fluency test there was an initial drop in performance from the first to the second time-slice but a consistent performance from that time on. The finding supports the notion of DLPFC compromise in schizophrenic subjects, and expands these observations to performance on both verbal and nonverbal tests of fluency.