Both processing speed and semantic memory organization predict verbal fluency in schizophrenia

Abstract

We systematically examined the relationship of both lexical retrieval and semantic memory organization to categorical verbal fluency performance in 40 outpatient schizophrenic subjects and 16 healthy controls. Mean choice reaction time (RT) on a lexical decision task was used as a measure of lexical retrieval efficiency. The complexity of semantic memory organization was measured using a Pathfinder semantic network analysis (calculated as the number of inter-node links obtained from a similarity rating task). In the schizophrenia group only, RT and semantic network links were each significantly negatively correlated with fluency and, together, accounted for 23% of the variance in fluency. RT and links were not significantly correlated with one another. Findings were unrelated to age, sex, education, or medication dose. Controlling for IQ reduced but did not abolish the relationship between fluency and network links. We conclude that the restricted verbal output of schizophrenic subjects is related both to impaired lexical retrieval and to variation in semantic memory organization, which partly reflects general intelligence. The statistical independence of the retrieval speed and organizational factors suggests that individuals with schizophrenia differ in the underlying processes that contribute to their reduced verbal fluency.