Oculomotor synchronization of visual responses in modeled populations of retinal ganglion cells.

We have recently shown that fixational eye movements improve discrimination of the orientation of a high spatial frequency grating masked by low-frequency noise, but do not help with a low-frequency grating masked by high-frequency noise (M. Rucci, R. Iovin, M. Poletti, & F. Santini, 2007). In this study, we explored the neural mechanisms responsible for this phenomenon. Models of parvocellular ganglion cells were stimulated by the same visual input experienced by subjects in our psychophysical experiments, i.e., the spatiotemporal signals resulting from viewing stimuli during eye movements. We show that the spatial organization of correlated activity in the model predicts the subjects' performance in the experiments. During viewing of high-frequency gratings, fixational eye movements modulated the responses of modeled neurons in a way that depended on the relative alignment of cell receptive fields. Responses covaried strongly only when receptive fields were aligned parallel to the grating's orientation. Such a dependence on the axis of receptive-field alignment did not occur during viewing of low-frequency gratings. In this case, the responses of cells on the parallel and orthogonal axes were similarly affected by eye movements. These results support a role for oculomotor synchronization of neural activity in the representation of visual information in the retina.