A comparison of verbal fluency tasks in schizophrenic patients and normal controls

Previous studies have reported significant impairment on verbal fluency tas ks (semantic and letter) among schizophrenic subjects. However, the possibi lity of specific categorical deficits has not been adequately investigated. Nor have the effects of task duration, the stability between testing sessi ons, and the relationship between intelligence and performance on fluency b een thoroughly studied. We performed a series of 3 min fluency tasks (seman tic/syntactic and letter) to determine whether duration specific or categor y-specific differences exist between schizophrenic subjects and normal cont rols. Each subject was tested at three different times as a means of estima ting word pool and assessing the stability of fluency output. Subjects were asked to generate exemplars from each of four semantic/syntactic categorie s (animals, tools, common nouns and verbs) and three letters (G, E and T). Data from 13 schizophrenic subjects and 15 sex-, age- and pre-morbid-IQ-mat ched control subjects revealed that patients' overall performance on both t he semantic and letter fluency tasks was impaired. While differential impai rment on specific semantic categories was noted between groups, no differen tial effects relating to task duration or testing session were present. Fur ther, by comparing the number of novel words produced in the three testing sessions, we found the groups to be equivalent, a finding we take to sugges t that schizophrenic patients' lexicon is intact. Covarying current IQ elim inated the group difference robustly for letter fluency, while only margina lly for semantic fluency. Our data revealed the presence of impairment in s emantic and letter fluency tasks in schizophrenic patients consistent with previous reports, and also that patients were differentially impaired on se mantic categories. (C) 2001 Elsevier Science B.V. All rights reserved.