During visual fixation, small eye movements keep the retinal image
continuously in motion. It is known that neurons in the visual system are
sensitive to the spatiotemporal modulations of luminance resulting from
this motion. In this study, we examined the influence of fixational eye
movements on the statistics of neural activity in the macaque's
retina during the brief intersaccadic periods of natural visual fixation.
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 spatial 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 support the hypothesis that
fixational eye movements, by shaping the statistics of retinal activity,
are an integral component of early visual representations.