A Neural Correlate for the Gap Effect on Saccadic Reaction Times in
Monkey.
Dorris, Michael C., and Douglas P. Munoz.
MRC Group in Sensory-Motor Physiology, Department of Physiology, Queen's
University, Kingston, Ontario Canada K7L 3N6.
APStracts 2:0071N, 1995.
SUMMARY AND CONCLUSIONS
1. The reduction in saccadic reaction time associated with the introduction of
a period of darkness between the disappearance of an initial fixation point
and the appearance of a new peripheral saccade target is known as the gap
effect. Fixation cells in the rostral pole of the monkey superior colliculus
have been implicated in the control of active visual fixation and suppressing
saccadic eye movements. To determine whether specific variations of fixation
cell discharge was correlated to the gap effect, we recorded the activity of
fixation cells while a monkey generated visually-guided saccades with various
temporal gaps between the disappearance of the initial fixation point and the
appearance of a peripheral saccade target. 2. The saccadic reaction times of
the monkey were shortest with gap durations of 200-300 ms and increased with
shorter or longer gap durations. The activity of fixation cells followed a
similar time course, having a minimum discharge rate 200-300 ms into the gap,
and increased activity at the time of target appearance with smaller or larger
gap durations. 3. We propose that the activity of fixation cells in the monkey
superior colliculus provide a neural correlate of the gap effect. The decrease
in activity of fixation cells 200-300 ms into the gap weakens the powerful
state of inhibition which they normally exert upon the saccade generating
system, allowing targets to be acquired at shorter reaction times.
Received 19 December 1994; accepted in final form 6 March 1995.
APS Manuscript Number J787-4.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 3 April 1995.