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Jacob Yates, Shanna Coop, Gabriel Sarch, Ruei-Jr Wu, Daniel Butts, Michele Rucci, Jude Mitchell; Beyond fixation: foveal receptive field estimation in freely viewing primates. Journal of Vision 2020;20(11):1470. doi: https://doi.org/10.1167/jov.20.11.1470.
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During natural vision, primates move their eyes constantly to position objects of interest onto the high-resolution region of the retina, the fovea. Eye movements also continue to occur even after objects are foveated, raising the question of how eye movements affect foveal processing of vision. Remarkably, despite the disproportionate importance of this region, we know very little about the response characteristics of neurons responsible for foveal vision. This is primarily the consequence of technical difficulty in mapping receptive fields in the fovea, which tend to be small and move with the eyes, even during the fixational periods in between saccades. Here, we combine high-resolution eye tracking, large-scale neurophysiology, and advanced statistical models to study foveal processing during natural visual behavior in neurons in primary visual cortex (V1) of marmoset monkeys. Using a digital Dual-Purkinje eye tracker (dDPI) that was recently developed in the Rucci lab, we can measure the eye position of marmosets with unprecedented precision. We record from multiple laminar electrode arrays that are semi-chronically implanted in the foveal representation in V1 while marmosets freely view large visual stimuli or search for small Gabor targets positioned randomly in the visual field. After correcting for the eye position offline, we reconstruct the retinal input for the neurons under study, which then forms the input for likelihood-based neural models. Using this approach, we can recover receptive-field subunits of foveal V1 neurons that are 1/10 of one degree of visual angle. Our statistical modeling approach additionally allows us to account for shared extra-retinal modulations of the neural population while simultaneously characterizing the response to the visual input. This approach opens the ability to study visual responses in the fovea in natural viewing contexts beyond standard fixation paradigms.
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