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Claudia Cherici, Murat Aytekin, Michele Rucci; Representing space in time during ocular drift. Journal of Vision 2014;14(10):198. doi: https://doi.org/10.1167/14.10.198.
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How is space represented in the visual system? In an immobile eye, a stationary stimulus is necessarily encoded by the pattern of active receptors in the retina. But the eyes are always in motion, even during fixation, and eye movements make spatial information available in the temporal domain. Our recent work has provided strong evidence that the visual system also uses the temporal modulations resulting from fixational eye movements to encode fine spatial detail (Rucci et al., 2007; Kuang et al., 2012). Here we investigated the mechanisms of this encoding process. Subjects viewed a standard Vernier stimulus in complete darkness through a narrow vertical aperture, which allowed exposure of only one line at a time. They reported whether the top line was to the left/right of the bottom one. The aperture was stabilized on the retina, so that no spatial cues existed on the retina and the exposure of the two lines was solely determined by ocular drift (trials with saccades/microsaccades were discarded). To successfully perform this task, knowledge of eye movement was necessary, as the temporal pattern on the retina was, by itself, ambiguous. We conducted three separate experiments. In the first experiment, stimuli were presented on a fast CRT monitor. In the second experiment, to rule out possible contributions from the CRT phosphor persistence, stimuli were delivered by an array of ultra-fast LEDs. In the third experiment, we used a different technique for retinal stabilization in which stimuli were viewed through deflecting mirrors. Results were similar in all experiments: performance was significantly above chance with offsets of a few arcminutes. These results reveal that spatial information exclusively contained in the temporal structure of fixational modulations suffices to discriminate fine patterns, even in the absence of spatial displacements.
Meeting abstract presented at VSS 2014
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