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We compared the performance of 44 patients with Parkinson's disease (PD), tested 12-24 h after withdrawal of dopaminergic medication, with 20 age-matched controls, on a verbal test for time estimation and in several time reproduction tasks. Patients with PD underestimated the duration of a time interval in the verbal time estimation task and showed overproduction of time intervals when required to reproduce a short time sample. Absolute errors were greater in the reproduction of longer time intervals in both control and PD patients, but especially in the latter. The presentation of time markers at faster rates had a detrimental effect on the performance of the patients but not of the controls. Patients with more severe PD performed worse on the time estimation and reproduction tasks compared with those with milder disease. Administration of levodopa-carbidopa (205/25 mg, p.o.) significantly reduced absolute errors in time estimation and reproduction in conditions where time markers were presented at the two faster rates of 5 Hz and 3.3 Hz. Performance in these two latter tests best discriminated patients and controls and had a positive significant association with simple reaction time and movement time. These results lead us to suggest that time estimation, i.e. the 'internal clock', is abnormally slow in PD.
Pastor et al. (Wed,) studied this question.