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Michele Rucci, Gaelle Desbordes, Antonino Casile; Fixational eye movements and retinal activity across multiple visual fixations. Journal of Vision 2008;8(6):348. doi: 10.1167/8.6.348.
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© ARVO (1962-2015); The Authors (2016-present)
During natural viewing, saccades alternate with brief periods of fixational eye movements. It has long been questioned whether the modulations of luminance resulting from eye movements might encode spatial information in the temporal domain. Correlated cell responses might signal the presence of important features in the visual scene such as an edge or an object. In the presence of natural visual stimulation, however, the visual system needs to distinguish the input correlations caused by relevant visual features from the “uninteresting” correlations generally present in natural scenes. Here, we examine the impact of fixational modulations of luminance on retinal activity across multiple fixation periods. The responses of parvocellular (P) and magnocellular (M) ganglion cells in different regions of the visual field were modeled while their receptive fields scanned natural images following recorded traces of eye movements. Immediately after the onset of fixation, wide ensembles of coactive ganglion cells extended over several degrees of visual angle, both in the central and peripheral regions of the visual field. Following this initial pattern of activity, the covariance between the responses of pairs of P and M cells and the correlation between the responses of pairs of M cells dropped drastically during the course of fixation. Cell responses were completely uncorrelated by the end of a typical 300-ms fixation. This dynamic decorrelation of retinal activity is a robust phenomenon independent of the specifics of the model. We show that it originates from the interaction of three factors: the statistics of natural scenes, the small amplitudes of fixational eye movements, and the temporal sensitivities of ganglion cells. These results suggest that the correlations in retinal activity present during visual fixation represent salient features in the scene which cannot be predicted from the second-order statistics of natural images.
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