0. ABSTRACT Previous studies have suggested that the cerebellum and basal ganglia may play a critical role in interval timing. In the first part of the chapter, we review this literature, focusing on production and perception tasks involving intervals in the hundreds of millisecond range. Overall, the neuropsychological and neuroimaging evidence consistently points to the involvement of the cerebellum in such tasks; the evidence is less consistent with respect to the basal ganglia. In the

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... half of the chapter, we present an experiment in which patients with either cerebellar or basal ganglia pathology were tested on a repetitive tapping task. Unlike previous studies, a pacing signal was provided, allowing an evaluation of variability associated with internal timing, motor implementation, and error correction. The results suggest a dissociation between the two groups: the patients with cerebellar lesions exhibited noisy internal timing while the gain in error correction was reduced in Parkinson patients. In combination with previous work, these results indicate how the cerebellum and basal ganglia may make differential contributions to tasks that require consistent timing.