Disproportionate impairment in semantic verbal fluency in schizophrenia: differential deficit in clustering.

The purpose of the current study was to investigate whether patients with schizophrenia present disproportionate impairment in semantic, relative to phonemic, fluency. Specifically, we explored whether this impairment could be explained by differential deficits in clustering or switching strategies. The Greek Verbal Fluency Test was administered to 119 patients with schizophrenia and 150 age-, education-, and gender-matched healthy controls. We calculated the total number of words generated, the number of cluster related words, and the number of switches on the semantic and phonological fluency tasks separately. Patients with schizophrenia generated fewer total words, cluster related words and switches than healthy controls on both fluency tasks. When controlling for the total number of words produced, however, the differences between the two groups in the number of cluster related words and switches disappeared. We found a disproportionate impairment in semantic, compared with phonemic, fluency in schizophrenia for total word production and the number of cluster related words, but not for the number of switches. In conclusion, patients with schizophrenia used the same strategies as healthy controls to perform on a word fluency test, but they used them less effectively. Disproportionate impairment in semantic fluency in schizophrenia resulted from a differential deficit only in clustering. Therefore, disproportionately impaired category fluency in schizophrenia may be primarily due to disorganization and not to inefficient access to and retrieval from semantic store.