On the existence of an attention-demanding process peculiar to simple reaction time: Converging evidence from Parkinson's disease

Abstract

Patients with Parkinson's disease tend to be slower at simple reaction-time (S.R.T.) tasks than age-matched controls. Some previous studies have shown an S.R.T. impairment where no prolongation of choice reaction time (C.R.T.) could be detected. Furthermore, S.R.T. and C.R.T. have been found to be pharmacologically dissociable in Parkinson's disease, with the S.R.T. deficit resistant to dopaminergic therapy. Such a deficit implies the existence of an underlying process which normally confers a specific advantage on S.R.T. performance but which may be selectively impaired in Parkinson's disease. Using a high-compatibility tactile R.T. task, we show that control subjects are more impaired in S.R.T. by the imposition of a secondary, oral reading task than Parkinsonian subjects. Indeed, under dual-task conditions, the usual Parkinsonian disadvantage in S.R.T. is abolished. In contrast, the deleterious effect of the secondary task on C.R.T. did not differ between the two groups. These findings converge on the notion that the Parkinsonian deficit in S.R.T. is due to impairment of an attention-demanding process which facilitates R.T. performance when the required response is known in advance. We offer some speculations about the nature of this process.