The Effects of Remote Distractors on Saccade Programming

Abstract

The time taken to initiate a saccade (latency) is increased under conditions in which a distractor is presented in the opposite visual field to the saccade target. We have termed this latency increase the ‘remote distractor effect’ (RDE). Conditions which produce the RDE are different from those used to demonstrate the ‘global effect’ amplitude modulation. In the global effect paradigm, distractors are presented in the same hemifield as the target and there is no effect on saccade latency. We report the results from a series of studies in which distractors were presented at various 2-D locations in both visual fields. Saccade latency was increased when distractors were presented in both visual fields, with the greatest increase for distractors at central fixation. Saccade latency was not affected by distractors presented on the horizontal axis in the same hemifield as the target, in which case the global effect was observed. For locations other than the horizontal axis, the critical location for modulating amplitude appeared to be within ±15 deg of the target location. Distractors presented outside this region increased latency but had no effect on amplitude. Furthermore, the latency increase observed was found to depend in a systematic way on the relationship between target and distractor eccentricities. Our data demonstrate that inhibitory processes similar to those thought to operate in the rostral pole of the superior colliculus may operate in other regions of the visual map.