Temporal preparation strategy may inflate RT deficit in patients with Parkinson's disease.

Twelve patients with Parkinson's disease (PD) and 12 age-matched controls completed a visual reaction time (RT) task to assess the effect of temporal parameters on response preparation. Simple and choice RT conditions were presented in separate blocks. In both conditions, preparatory intervals of various durations (1, 3 and 5 s) were introduced between an auditory warning signal and the visual target. Within a block of trials, intervals varied randomly. The results indicated that PD patients responded slower than controls in both task conditions. Also, there was evidence for preparation in both groups, as RT decreased with increasing intervals. A three-way interaction indicated that PD patients' RT was longer than that of controls at the shortest interval in simple RT. This suggests that PD patients show a different pattern of temporal response preparation and that this may contribute to their deficit on RT tasks.