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Michele Rucci, Jonathan D. Victor, Murat Aytekin; Temporal whitening of retinal input during natural head-free fixation. Journal of Vision 2013;13(9):1231. doi: 10.1167/13.9.1231.
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During natural fixation, microscopic head and eye movements keep the retinal image continually in motion. In a recent study (Kuang et al., 2012), we have shown that, during viewing of natural scenes, fixational eye movements carry out a crucial information-processing step: they remove predictable correlations in natural scenes by equalizing the spatial power of the retinal image within the frequency range of ganglion cells’ peak sensitivity, a transformation, previously attributed to center-surround receptive field organization. In this previous study, to accurately record microscopic eye movements, subjects examined natural scenes with their head immobilized. Here we extend this work by examining the characteristics of the retinal input during natural head-free fixation. To this end, we used a database of previously recorded head and eye movements, collected by means of the Maryland Revolving Field Monitor, a high resolution eye-tracker which is little influenced by head translations (Steinman, 2003). Observers (N=4) looked sequentially at LED targets positioned randomly on a table in front of them, while their eye movements were recorded by means of coils, and their head position was measured by means of coils and a distance detection system. In agreement with previous reports, the image moved considerably on the retina, reaching speeds of 11 deg/sec (median 3 deg/sec), a continuous motion frequently interrupted by joint head/eye saccades. We selected periods in between saccades and estimated the spatiotemporal power spectrum of the retinal input. Results were highly similar to those previously obtained with the head immobilized. Fixational instability transformed spatial patterns of luminance into temporal modulations in a way that counterbalanced the spectral distribution of natural images and equalized the power of the retinal image over a wide range of spatial frequencies. These results further support the proposal that fixational behavior is an important component of the encoding of visual information.
Meeting abstract presented at VSS 2013
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