ABNORMALITIES OF PREDICTIVE SACCADES IN PARKINSONS-DISEASE

SACCADES of patients with mild Parkinson's disease (PD) are said to be abnormal in the absence of a concurrently visible target or when they are part of a rapid sequence of eye movements. We tested this hypothe sis using a predictive saccade paradigm in which target visibility is withdrawn for a period. Three rates of target alternation were used (0 .25 Hz, 0.5 Hz and 1.0 Hz). Withdrawal of target visibility brought ou t the extremes of primary saccade gain for both the controls and the p atients with PD, most undershoot being displayed at the lowest frequen cy, whereas the gain was greatest at the highest frequency, actually o vershooting the target location. These results demonstrate that the sp atial error of parkinsonian saccades does not invariably take the form of hypometria when part of a rapid sequence of eye movements.