A meta-analytic review of verbal fluency deficits in schizophrenia relative to other neurocognitive deficits

INTRODUCTION: A prominent view in the neuropsychological literature is that schizophrenia is particularly associated with executive dysfunction, yet in a meta-analytic review it was concluded that, relative to their general level of intellectual functioning, schizophrenics are not disproportionately impaired on a measure of this construct, the Wisconsin Card Sorting Test (WCST). However, verbal fluency tests may be more valid measures of executive functioning as they are more sensitive to the presence of focal frontal lobe injuries. METHOD: A meta-analysis was conducted on 84 studies comparing the performance of schizophrenics and healthy controls on tests of phonemic and semantic fluency, as well as other cognitive measures presumed to impose only minimal demands on executive functioning. RESULTS: Neither phonemic or semantic fluency deficits qualified as differential deficits relative to general intelligence or psychomotor speed. Patients with schizophrenia were significantly more impaired on semantic relative to phonemic fluency. CONCLUSIONS: As for the WCST, deficits on tests of verbal fluency reflect a more generalised intellectual impairment and not particular difficulties with executive control processes. The larger deficit for semantic relative to phonemic fluency suggests that, in addition to general retrieval difficulties, schizophrenia is associated with compromises to the semantic store.