IRRELEVANT PERIPHERAL VISUAL-STIMULI IMPAIR MANUAL REACTION-TIMES IN PARKINSONS-DISEASE

In three experiments, the effects of irrelevant visual information on the time to initiate and to complete a simple movement of the hand in response to a visual signal were studied in patients with a diagnosis of Parkinson's disease, and in age-matched normal controls. Subjects g azed at the centre of a TV monitor and were instructed to move their p referred hand from one metal plate to another as soon as a a blue disc appeared in the centre of the screen. This control condition was comp ared with other conditions in which the surrounding area of the screen was simultaneously filled with fields of irrelevant discs, which in E xperiment 1 were either stationary, or streamed out from or in towards the centre of the screen, Reaction times, but not movement times, wer e significantly slowed in the patients (but not the controls) by the i rrelevant disc fields. When the irrelevant dots were continuously pres ent (between as well as within trials-experiment 2), they had no effec t on RT, When they were present between trials, but turned off as the movement signal was turned on, RT was again slowed in patients, The re sults are discussed in relation to the akinesia (''freezing'') experie nced by some patients in confined spaces (such as doorways), and to po ssible abnormalities of visual cortical and striato-nigro-collicular a ctivity. (C) 1997 Published by Elsevier Science Ltd.