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Martina Poletti, Michele Rucci; Fixational eye movements and retinal activity during a single visual fixation. Journal of Vision 2008;8(6):280. doi: https://doi.org/10.1167/8.6.280.
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© ARVO (1962-2015); The Authors (2016-present)
In the intervals between saccades, small saccades and drifts modulate the spatiotemporal stimulus on the retina. It has long been questioned whether the modulations of luminance resulting from fixational eye movements might encode spatial information in the temporal domain. Here, we examine the impact of fixational modulations of luminance on retinal activity during a single fixation interval. We have recently shown that fixational eye movements improve the discrimination of high spatial frequency gratings masked by low-frequency noise, but do not help in the discrimination of low-frequency gratings masked by high-frequency noise. In this study, we model retinal activity in the presence of the same visual input experienced by subjects in our experiments, i.e. the spatiotemporal signals resulting from viewing stimuli during eye movements. Spatiotemporal filters designed on the basis of neurophysiological data modeled the responses of parvocellular ganglion cells in the macaque's retina. We show that synchronous modulations in cell responses resulting from fixational instability are consistent with psychophysical results. During presentation of high-frequency gratings, oculomotor activity influenced the correlation between pairs of cells in a way that depended on the relative alignment of cell receptive fields. Cell responses were strongly correlated only when their receptive fields were aligned parallel to the grating's orientation. Such a dependence on receptive-field alignment was instead absent during viewing of low-frequency gratings. That is, in keeping with the subjects' reports, fixational eye movements synchronously modulated arrays of RGCs parallel to the grating's orientation during viewing of high-frequency gratings masked by low-frequency noise, but not during presentation of low-frequency gratings masked by high-frequency noise. Changes in the structure of correlated activity occurred without affecting average firing rates. Synchronous modulations resulting from fixational eye movements appear to be an important component of the way visual information is encoded in the early visual system.
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