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* To whom correspondence should be addressed. E-mail: Brian.J.White{at}psychol.uni-giessen.de.
It has been suggested that the remote distractor effect is the result of non-target stimulation of a central region representing a collicular fixation zone near the time of target onset. The distributed network of the cells responsible for this effect is believed to extend over a large area, responding to distractors up to 10 deg in the periphery. Several studies also implicate the superior colliculus as the substrate behind an inhibited saccadic response due to a display change. We investigated this further by using a patch of pink noise of various sizes as a non-target stimulus. We show that the onset of a small patch (2.3 x 2.3 deg) of centrally displayed pink noise can produce a significant increase in saccadic latency to a simultaneously presented peripheral gabor-target. In contrast, a large patch (36 x 36 deg) of pink noise did not increase latency despite the fact that it also stimulated the region representing the fixation zone. Furthermore, only the large patch of noise facilitated latency when presented prior to target onset. We also examined the effect of patch sizes between these two extremes and found a steady decrease in latency as patch size increased. This confirms that non-target stimulation of the region representing the fixation zone near the time of target onset is not in itself sufficient to produce the increase in latency typically found with remote distractors. The results are consistent with the idea that only a spatially confined object leads to a discharge of collicular fixation neurons.
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