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Abstract:
Primates can generate saccades to a stimulus which serves as
the target of the movement (congruent), and saccades where the
stimulus serves as a landmark for an instructed movement
(incongruent). We investigated the properties of congruent and
incongruent saccades by training monkeys on a task with pro- and
anti-saccade trials. Depending upon the color of the initial
fixation point, they generated a pro-saccade towards a visual
stimulus or an anti-saccade away from the stimulus to its mirror
position. In each block of trials, the stimulus appeared
pseudorandomly at one of two diametrically opposite locations. On
half of the trials, the fixation point disappeared 200 msec before
stimulus presentation (gap condition) and on the remaining trials,
the fixation point remained visible (overlap condition). Stimuli
were presented in blocks of eight directions at five amplitudes
ranging from 2 - 16o. The main findings were: 1) Anti-saccades had
longer latencies than pro-saccades; 2) anti-saccades had lower
velocities than pro-saccades; 3) anti-saccades were more hypometric
than pro-saccades; 4) pro- and anti-saccades had faster reaction
times in the gap than in the overlap condition; 5) direction errors
on anti-saccade trials were more frequent in the gap condition than
in the overlap condition. In summary, many characteristics of
monkey anti-saccades were similar to those described in previous
human studies.
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