Ideational fluency as a domain of human cognition.

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 on overlapping cortical circuits. Despite differences in the tasks used to assess it, we hypothesized that ideational fluency represents a dissociable dimension of human cognition.Altogether, 317 healthy adults and 280 adults with medical or psychiatric illnesses completed a cognitive test battery that included three measures of ideational fluency. Principal component analyses assessed the factor loadings of these fluency measures along with 10 other cognitive test scores. A series of hierarchical multiple regressions determined the relative contribution of the other fluency measures to the fluency variable of interest after accounting for demographic factors and other cognitive abilities.In both participant groups all three measures of word and design fluency loaded on a single factor. An ideational fluency composite score was also normally distributed among healthy adults. After accounting for demographic characteristics, intelligence, processing speed, memory, and executive functioning, adding terms for letter- and category-cued word fluency improved multiple regression models predicting design fluency and vice versa.Despite differences among them, the three fluency measures emerged as clearly distinct from other cognitive abilities. Alternate fluency measures also accounted for significant incremental variability in both word and design fluency, even after accounting for other cognitive abilities. Thus, word and design fluency appear to involve a distinct and dissociable, material-independent dimension of cognitive processing, namely ideational fluency.