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A. Ma-Wyatt, M. Morrone, J. Ross; Saccadic Compression of Visual Space Is Significantly Influenced by Retinal Illumination . Invest. Ophthalmol. Vis. Sci. 2003;44(13):4105.
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Purpose: If a bar is flashed just before a subject starts to make a saccade, subjects mislocalise its position in space when making a verbal report but not if they point with hand unseen (Burr, Ross and Morrone, 2001). We have demonstrated that compression can occur for both verbal report and pointing if a blinding flash – providing light but no visual references – occurs shortly after the initiation of a saccade We investigated whether this distinction between responses for perception and action is contingent upon the duration of a delay before responding, or whether it was due to light level. Methods: Subjects made a 15° horizontal saccade. A bar was flashed just before the subject started to make the saccade, and after the target to saccade to was presented. Subjects viewed a touchscreen through a liquid crystal shutter. The shutter closed at a variable duration after the initiation of a saccade. Subjects were tested either in the dark, or with a blinding flash yoked to the closing of the shutter. Subjects made either a verbal report of the perceived position of the bar, or pointed with hand unseen. Results: Compression for verbal report was found both in the dark and with a flash, consistent with earlier findings. Compression for pointing was present if a flash occurred, or at very long shutter durations but not in the dark. Conclusions: A dissociation between compression for verbal report and pointing may be dependent on retinal illumination at the time of response.
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