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Delphine Massendari, Matteo Lisi, Patrick Cavanagh, Thérèse Collins; Is the efference copy of a saccade influenced by a perceptual illusion?. Journal of Vision 2017;17(10):879. doi: 10.1167/17.10.879.
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The double-drift stimulus leads to a large discrepancy between the physical path of a moving Gabor and its perceived direction. Surprisingly, saccades to the double-drift stimulus do not show any effect of the illusion (Lisi & Cavanagh, 2015). Here, we asked whether the efference copy of the saccade was influenced by the illusion. This question was addressed by using saccadic suppression of displacement. We presented a single Gabor moving along a linear trajectory with internal motion (double-drift condition) or without (control condition). In the double-drift condition, the perceived orientation of the path could deviate by 45° or more from its physical path while in the control condition the physical and the perceived paths were the same. During stimulus presentation, participants keep their eyes focused on a fixation dot while the drifting Gabor appeared and moved in the periphery. After 1800 ms of stimulus presentation, the fixation dot was removed, serving as the go-signal to make a saccade toward the moving Gabor. As soon as a saccade was detected, a blank of 250 ms occurred after which the Gabor reappeared and remained stationary at a new location to the left or the right of its original location. Participants were asked to report the direction of the jump. We hypothesized that if the expected post-saccadic target location is influenced by the illusion, we should observe a shift in the psychometric function of displacement judgment for the double-drift, compared to the control condition. Indeed, the psychometric function of the double-drift condition was shifted by about 0.5° compared to that of the control condition. Thus, displacement judgments were affected by the illusion, suggesting that the perceived location plays a role in the predicted location of the target after a saccade even though it has little effect on the saccade itself.
Meeting abstract presented at VSS 2017
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