The pervasive 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 investigated the individual differences in linguistic and domain-general skills that support verbal fluency and lead to this variability. In particular, we focused on the role of linguistic knowledge, which was calculated through six tests capturing vocabulary, amount of reading, and knowledge of grammar rules. We compared this to the role of three key domain-general skills: working memory (WM), processing speed, and nonverbal reasoning (IQ). 571 young native Dutch speakers completed semantic (category) and phonemic (letter) VF tasks, along with an individual differences test battery. We assessed the VF trials for the total number of correct words as well as two temporal variables, the time to first response and the time by which half of the responses have been produced. Linear mixed effects models revealed that linguistic knowledge was the strongest predictor of performance across all scores, and it had a larger effect than the domain-general skills. We discuss the role of linguistic knowledge and how it shapes the mental lexicon, concluding that better language skills lead to more efficient and detailed associative links between words that share semantic or phonological/orthographic features. We also provide updated norms for VF performance in Dutch and practical suggestions for using the task.