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David Richters, Ehud Ahissar, Michele Rucci; Temporal encoding of visual space by means of fixational eye movements. Journal of Vision 2010;10(7):559. doi: https://doi.org/10.1167/10.7.559.
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The processing of fine detail in moving stimuli appears to rely on information encoded in the temporal domain. During natural fixation, all stimuli continually move on the retina because of perpetual eye movements. Retinal motion caused by eye movements allows for the possibility of encoding and decoding spatial information in the temporal domain (Ahissar, 2001). In this study, we examined whether temporal modulations caused by ocular drift contribute to spatial perception. Observers viewed a standard Vernier two-line stimulus through a narrow, digital, retinally-stabilized aperture. The aperture was too narrow for both lines of the stimulus to be seen at once, and it moved synchronously with the observers' eye, allowing only a thin fixed vertical stripe of the retina to be stimulated. In each trial, the top line of the Vernier stimulus was randomly selected to be either on the left or on the right of the bottom line. Thus, as the observers' eye moved from left to right, the upper line would be seen first for one stimulus arrangement (top-left) but second for the other arrangement (top-right). The order of line exposures and the timing difference between exposures was determined solely by eye movements. Only fixational drift allowed the lines to be seen; saccades and microsaccades were identified in real time and the stimulus was not displayed during these movements. We show that observers can use the temporal modulations caused by ocular drift to make accurate spatial judgments. This research provides a direct link between fixational eye movements and visual perception and shows that temporally-encoded spatial information resulting from eye movements is useful and accessible to the visual system.
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