Motivational effects on motor timing in attention-deficit / hyperactivity disorder.

OBJECTIVE: This study was designed to clarify whether poor performance of children with attention-deficit/hyperactivity disorder (ADHD) on motor timing tasks reflects a true deficit in the temporal organization of motor output or is due to a lack of intrinsic motivation. METHOD: Eighteen children with ADHD (age 8-12) were compared with 18 age- and gender-matched normal controls with respect to timing precision, timing variability, and the frequency of extreme under- and overestimations during a 1-second interval production task. Monetary reward, response cost, and no reward were implemented to manipulate motivation. RESULTS: Children with ADHD produced significantly more inaccurate and more variable time intervals and exhibited a larger number of extreme over- and underestimations than control children. Although all children performed significantly better when monetary incentives were applied, group differences were not eliminated. CONCLUSIONS: In this study, no evidence was found for a motivational deficit as an explanation for impaired performance on a time production task in ADHD. Rather, results provide clear support for a generic motor timing deficit, probably due to a dysfunctional frontostriatocerebellar network involved in temporal aspects of motor preparation.