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Sabine Born, Dirk Kerzel; Stimulus contrast and the remote distractor effect: differential effects for foveal and peripheral distractors. Journal of Vision 2008;8(6):119. doi: 10.1167/8.6.119.
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It is well known that a distractor stimulus presented simultaneously with the saccade target prolongs saccadic latency (remote distractor effect, RDE). We examined the influence of target and distractor contrast on the RDE. Subjects were asked to make a saccade to a target Gabor presented either to the left or right of a central fixation stimulus. Distractors were likewise Gabors and presented either foveally or peripherally (contralateral to the target) after offset of the fixation stimulus.
For foveal distractors, the influence of distractor contrast was minimal. However, the RDE increased with increasing target contrast. For low target contrasts, even negative RDE values were observed, i.e. shorter latencies in the presence of a distractor compared to the no distractor control condition. We suggest that this facilitation was due to a general increase in saccadic latency for low target contrasts. We conclude that the distractor serves two complementary functions: first it acts as a true distractor, sparking a rapid but transient perturbation of saccade initiation. Second, it acts as a warning signal for target appearance, facilitating saccade initiation. As this latter effect builds up slowly, it is only observed for targets yielding long latencies or when the distractor is presented well before the target.
For peripheral distractors, we obtained inverse results: there was no significant effect of target contrast, but the RDE increased for increasing distractor contrast. We argue that the discrepant results for foveal and peripheral distractors do not contradict the notion of a uniform saccade map in the superior colliculus in which fixation neurons in the rostral pole form an extension of the caudal build-up cells. Rather, the stronger foveal input at the rostral pole compared to peripheral input at more caudal sites might account for the discrepancies.
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