Perceptual timing in cerebellar degeneration.

This study examined time perception in 12 patients with cerebellar degeneration (CD) and in 13 normal controls (NC). We used a time bisection procedure with four interval conditions (100-900 msec; 8-32 sec; 100-600 msec; 100-325 msec). Each subject's bisection point, discrimination ability (the Weber ratio) and precision (the inverse of the proportion of unexplained variance) was calculated for each condition. CD patients' performance on the 100-900 msec time bisection condition suggested a possible time discrimination deficit, which was confirmed with intervals in the range of 100-600 msec. Time discrimination was normal on the 100-325 msec condition and impaired on the 8-32 sec bisection task. However, when discriminating long intervals, CD patients also showed a precision deficit, which points to impaired sustained attention and/or decision processes. Our findings corroborate the view that cerebellar timing processes are not limited to the motor system but are also used in perceptual computations.