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Chih-Yang Chen, Claudia Distler, Klaus-Peter Hoffmann, Ziad Hafed; Functional and structural organization of the foveal visual representation of the primate superior colliculus. Journal of Vision 2017;17(10):739. doi: https://doi.org/10.1167/17.10.739.
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A primary reason for using non-human primates in visual neuroscience is their foveated retina. However, neurophysiological investigations of foveal representations are not common because of difficulties with eye movements and small response fields (RF's). This creates a pressing need to study foveal representations, especially given that foveal processing is the mode of operation that we rely on most heavily in our daily life. Here we recorded from the foveal visual representation of the superior colliculus (SC) in 2 awake and 3 anesthetized monkeys. In the awake animals, we recorded from 70 neurons with preferred eccentricities < 1 deg and compared their visual RF characteristics to those of >100 more eccentric neurons. We corrected for eye position during fixation to obtain better estimates of RF shapes and sizes. In the anesthetized animals, we densely mapped preferred RF locations and related them to SC anatomy. We systematically moved our electrodes by 100, 250, or 500 micrometer steps in both rostral-caudal and medial-lateral axes. We found that foveal SC neurons' RF's were strongly skewed and lateralized, having sharp cutoffs at the "foveal edge" of the visual representation. RF skew decreased progressively with eccentricity, along with an exponential increase in RF size. Our dense mappings also revealed very orderly foveal representation topography, which is continuous with the well-known peripheral SC topography. We used our mappings to develop a 3-D model of the topographic foveal SC representation. Our results demonstrate strong laterality of visual representations in the foveal SC, and fairly large magnification of foveal space in SC tissue, even larger than that used in current models of SC topography. The magnification and continuity of foveal topography at this level of detail have implications on the potential impacts of small eye movements on visual coding, and might also explain certain characteristics of microsaccade amplitude distributions.
Meeting abstract presented at VSS 2017
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