Ideational fluency as a domain of human cognition

Objective: Many disorders are characterized by impoverished ideational fluency. Tests of letter word,category word, and design fluency likely invoke different cognitive processes, but they might depend onoverlapping cortical circuits. Despite differences in the tasks used to assess it, we hypothesized thatideational fluency represents a dissociable dimension of human cognition. Methods: Altogether, 317healthy adults and 280 adults with medical or psychiatric illnesses completed a cognitive test battery thatincluded three measures of ideational fluency. Principal component analyses assessed the factor loadingsof these fluency measures along with 10 other cognitive test scores. A series of hierarchical multipleregressions determined the relative contribution of the other fluency measures to the fluency variable ofinterest after accounting for demographic factors and other cognitive abilities. Results: In both participantgroups all three measures of word and design fluency loaded on a single factor. An ideationalfluency composite score was also normally distributed among healthy adults. After accounting fordemographic characteristics, intelligence, processing speed, memory, and executive functioning, addingterms for letter- and category-cued word fluency improved multiple regression models predicting designfluency and vice versa. Conclusions: Despite differences among them, the three fluency measuresemerged as clearly distinct from other cognitive abilities. Alternate fluency measures also accounted forsignificant incremental variability in both word and design fluency, even after accounting for othercognitive abilities. Thus, word and design fluency appear to involve a distinct and dissociable, materialindependentdimension of cognitive processing, namely ideational fluency.