The psychological refractory period in Parkinson's disease

The Psychological Refractory Period paradigm was used to investigate whether patients with Parkinson's disease showed disproportional deficits in regulating responses totwo sequential presented stimuli. The first task required a speeded key-press response to an auditory stimulus, and the second task required a speeded key-press response to a visual stimulus. The stimulus onset asynchrony (SOA) between Task 1 and Task 2 was 50 msec., 150 msec., and 650 msec. According to the bottleneck model, the SOA manipulation should not affect performance on Task 1, but reaction time for Task 2 should increase as the SOA between the two tasks decreased. The increase in reaction time for Task 2 was referred to as the Psychological Refractory Period. In this study, both patients with Parkinson's disease and normal controls showed classical effects. More importantly, although the 22 patients with Parkinson's disease took longer to respond to both Tasks 1 and 2 than the 20 normal controls, the effects of the Psychological Refractory Period for the two groups were of the same magnitude. The results suggest that Parkinson's disease affects only the response-execution stages rather than the response-selection stages, based on the central bottleneck model.