Clustering and switching on verbal and figural fluency functions in adults with attention deficit hyperactivity disorder.

Introduction: Neuropsychological studies of adult patients with ADHD have revealed marked disturbances of executive functions including impairments of attention, working memory, impulsivity, shifting, and divergent thinking. Phonemic fluency tasks, in particular, have been shown to be sensitive measures for the assessment of executive functions of adults with ADHD.

Methods: The present study has examined figural fluency and both phonemic and semantic verbal fluency in 34 adult patients with ADHD and 34 healthy participants. For evaluation of fluency performance the number of words or designs, the number of repetitions and the number of deviations from test rules were calculated. Furthermore, clustering strategies and switching responses were analysed. In comparison with healthy participants, patients with ADHD produced significantly fewer words or designs, but they did not differ from healthy participants in the number of repetitions or rule violations.

Results: Analysis of switching and clustering showed that patients produced significantly fewer switching responses on both verbal fluency tasks, although patients tended to generate smaller clusters. Switching on the figural fluency task was unimpaired.

Conclusions: The results of the present study suggest that adult patients with ADHD may suffer from a dysfunction that may affect retrieval processes and the categorisation of knowledge.