Rucci M, Casile A, 2005, "Possible influences of fixational eye movements on the neural encoding of natural stimuli" Perception 34 ECVP Abstract Supplement
Possible influences of fixational eye movements on the neural encoding of natural stimuli
M Rucci, A Casile
It is a long-standing proposal that an important function of the early stages of the visual system is to discard part of the redundancy of natural scenes to establish compact visual representations. In particular, it has been observed that the response characteristics of neurons in the retina and LGN may attenuate the broad correlations that characterise natural scenes by processing input spatial frequencies in a way that counterbalances the power-law spectrum of natural images. Here, we extend this hypothesis by proposing that the movement performed by the observer during the acquisition of visual information also contributes to this goal. During natural viewing, the projection of the stimulus on the retina is in constant motion, as small movements of the eye, head, and body prevent the maintenance of a steady direction of gaze. To investigate the possible influence of a constantly moving retinal image on the neural coding of visual information, we have analysed the statistics of retinal input when images of natural scenes were scanned in a way that replicated the physiological instability of visual fixation. We show that during visual fixation the second-order statistics of input signals consist of two components: a first element that depends on the spatial correlation of the stimulus, and a second component produced by fixational instability, which, in the presence of natural images, is spatially uncorrelated. By interacting with the dynamics of cell responses, this second component strongly influences neural activity in a model of the LGN. In the presence of fixational instability, the responses of simulated cells become decorrelated even if their contrast sensitivity functions are not tuned to counterbalance the power-law spectrum of natural images. The results of this study suggest that fixational instability contributes to the establishment of efficient representations of natural stimuli.
[Supported by NIH grant EY15732-01 and NSF grant BIC-0432104.]
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