Initiation of saccades during fixation or pursuit: Evidence in humans for a
Krauzlis, R.J. and F.A. Miles.
Laboratory of Sensorimotor Research, National Eye Institute, National
Institutes of Health, Bethesda, MD.
APStracts 3:0178N, 1996.
SUMMARY AND CONCLUSIONS
1. In four human subjects, we measured the latency of saccadic eye movements
made to a second, eccentric, target after an initial, foveated, target was
extinguished. In separate, interleaved trials, the targets were either both
stationary ("fixation") or both moving with the same velocity ("pursuit"). For
both fixation and pursuit trials, we extinguished the first target at
randomized times during maintained fixation or pursuit and varied the time
interval ("gap duration") before the appearance of the second target.
2. During both fixation and pursuit, the presence of a 200-ms gap reduced the
latencies of saccades, compared to those obtained with no gap. For two
subjects, we imposed additional, intermediate, gap durations and found that
saccade latencies varied as a function of gap duration. Furthermore, the
latencies of saccades elicited during pursuit displayed the same dependence on
gap duration as those elicited during fixation. 3. Our results demonstrate
that the "gap effect" observed for saccades made during fixation also occurs
for saccades made during pursuit. To the extent that the gap effect on saccade
latency reflects a mechanism underlying the release of fixation, our results
suggest that the same mechanism is invoked for saccades made during pursuit.
From the viewpoint of initiating saccades, the existence of separate fixation
and pursuit systems may be irrelevant.
Received 17 July 1996; accepted in final form 16 August 1996.
APS Manuscript Number J562-6.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 19 September 1996