In order to determine the influence of perceptual\ninput upon oculomotor responses, we examined rapid\nsaccadic eye movements made by healthy human observers\nto a virtual target defined by the extrapolated intersection\nof a pointer with a distant landing line. While corresponding\nperceptual judgments showed no evidence of systematic\nbias, eye movements showed a strong bias, in the direction\nof assimilation of the saccade trajectory to the shortest\npath between the end of the pointer and the landing line.\nAdding an abutting vertical inducing line to make an angle\nof 45 deg with the pointer led to a larger bias in the same\ndirection as the classical Poggendorff illusion. This additional\nPoggendorff effect was similar in direction and magnitude\nfor the eye movements and the perceptual responses.\nLatency and dynamics of the eye movements were closely\nsimilar to those recorded for a control task in which observers\nmade a saccade from the start fixation to an explicit target\non the landing line. Further experiments with inducing\nlines presented briefly at various times during the saccade\nlatency period showed that the magnitude of the saccade\nbias was affected by inducer presentation during the saccade\nplanning process, but not during the saccade itself.\nWe conclude that the neural mechanisms for extrapolation\ncan feed into the control of eye movements without obvious\npenalties in timing and accuracy and that this information\ncan instantaneously modify motor response throughout\nthe planning phase, suggesting close association between perceptual and motor mechanisms in the process of visuospatial\nextrapolation.
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