The role of linguistic knowledge in verbal fluency tests: How individual differences in language skills shape the mental lexicon.

“List as many words as you can that start with M.” The verbal fluency (VF) task is simple, yet even a typical university student only manages to produce about 15 words within one minute, and there is substantial variability around this mean. We examined which individual difference factors best predict this variability, focusing on the contributions of linguistic knowledge and domain-general skills. 571 young native Dutch speakers completed semantic (category) and phonemic (letter) VF tasks, along with an individual differences test battery. Linguistic knowledge was assessed through a composite of six tests measuring vocabulary, reading experience, and grammar knowledge, and compared to short-term/working memory, processing speed, and nonverbal reasoning. We assessed the VF trials for the total number of correct words as well as two temporal variables, the time to first response and a proxy for the time by which half of the responses had been produced. Mixed effects modeling showed that linguistic knowledge predicted the total number of correct responses in both semantic and phonemic VF. Short-term/working memory and processing speed were also significant predictors, but with smaller estimated effect sizes. The temporal variables showed little effect of linguistic skills. We discuss how linguistic knowledge shapes the structure of the mental lexicon such that it affects both meaning-driven and form-driven access to lexical items. Finally, we provide updated norms for VF performance in Dutch and practical suggestions for using the task.