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Alby Richard, Jan Churan, Daniel Guitton, Christopher Pack; Perceptual compression during head-free gaze shifts: visual and extraretinal contributions. Journal of Vision 2008;8(6):217. doi: 10.1167/8.6.217.
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© ARVO (1962-2015); The Authors (2016-present)
Saccadic eye movements are accompanied by a transient distortion of perceptual space, traditionally attributed to errors in extraretinal mechanisms that preserve spatial constancy across eye movements. This perisaccadic mislocalization of visual space, so far studied in head-fixed subjects, comprises a compression of visual space towards the saccade target, along with a shift in the direction of the saccade (Ross et al., 1997) and a saccade-velocity dependence (Ostendorf et al., 2007). Here we asked whether these mechanisms occur when head motion contributes to a gaze shift. We used a head-unrestrained paradigm, in which both amplitude and velocity could be varied, and found a powerful compression of visual space that depended on both the gaze velocity and the time at which the localization target was presented relative to the onset of the gaze shift. Compression of visual space always occurred towards the intended gaze target, which was not necessarily the endpoint of the eye saccade component of a gaze movement. Furthermore, the magnitude and the latency of the peak perceptual compression increased as the amplitude of a gaze shift increased from 10 to 40 degrees. Across all conditions, there was also a strong correlation between the time of peak compression and the time of maximum gaze velocity. We also observed greater compression when the localization target was lower in contrast, and this effect became more pronounced for larger gaze shifts. The effect of reducing contrast was similar to that of increasing gaze shift velocity, suggesting that retinal events which reduce stimulus visibility increase perisaccadic compression. However, even when velocity and contrast were constant, perceptual compression increased with the amplitude of the gaze shift, indicating that extraretinal mechanisms contribute significantly to the perisaccadic perception of visual space.
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