The saccadic eye movements of nine patients with Parkinson’s disease were
compared to those of nine age-matched controls in two paradigms generating
volitional saccades. In both paradigms. subjects had to make delayed
saccades to peripheral LED targets: a peripheral target appeared 700 msec
before a buzzer sounded, the buzzer being the signal to make a saccade to
the target. In the first paradigm (“centre-off“), the fixation target was
extinguished simultaneously with buzzer onset. In the second (“centreremain”)
it was not extinguished until 1000 msec later. The results showed
that for outward saccades in both paradigms, there was no difference between
Parkinsonian patients and controls, but saccadic latencies were significantly
shorter in the “centre-remain” paradigm. The initial outward saccades were
indistinguishable from the normal, reflex saccades of the same subjects.
However, saccades returning to the centre (a type of remembered target
saccade) were hypometric and showed multistepping. Both effects were more
pronounced in patients with Parkinson’s disease. The significance of these
findings in terms of current hypotheses about the nature of the Parkinsonian
saccadic deficit is discussed.