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Zhi-Lei Zhang, Clifton Schor; Temporal properties of monocular perisaccadic spatial distortion. Journal of Vision 2007;7(9):584. doi: 10.1167/7.9.584.
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It has been shown that eye movement can distort space percept before and during saccade. We have demonstrated in previous study that stereopsis can be evoked by head-centric disparity due to the eye movement even though there was no retinal disparity. In this study we tested how the perceived visual direction changed with time immediately before the saccade that causes the visual direction of a stationary target to appear to be displaced in the direction of the saccade (Ross et al., 1997). Two flashes with an inter-stimulus interval of 50ms were presented briefly (3ms) to the same eye before saccade onset. We compared the perceived positional displacement of the two briefly flashed zero-horizontal offset targets as a function of the TSO. The TSO (Time to Saccade Onset) is defined as the time difference between the onset of the saccade and the onset of the second flash. The bigger the TSO, the earlier the flash was presented before the saccade onset. We found that even though the retinal horizontal position is the same for the two flashes they appear to be displaced with TSO up to 20ms, in which, the first flash displaced more than the second toward the saccade target. We didn't find the reverse of the temporal order (Morrone et al 2005) of the two flashes with TSO range from 0 to 60ms. This result demonstrated that the perceived visual direction varies before the saccade onset due to the dynamic of the eye position signal component. The result supported the theory of the head-centric disparity.
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