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Alexandra E. Boehm, Brian P. Schmidt, Dennis M. Levi, Austin Roorda; The spatial extent of desensitization to repeated light stimulation on the retina. Journal of Vision 2019;19(8):25. doi: https://doi.org/10.1167/19.8.25.
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When a stimulus is stabilized on the retina, it fades completely from perception. Interestingly, stimuli that are stabilized in retinal space but modulated in intensity over time, i.e. flickered stimuli, also fade. Repeated stimulation of the retina with brief flashes of light has been shown to cause a localized reduction in visual sensitivity that cannot be explained by light adaptation at the receptor level (Frome et al. 1981). We hypothesized that the spatial extent of desensitization might reflect the spatial characteristics of the receptive fields of the post-receptoral mechanism. To investigate this, we used a scanning laser ophthalmoscope to simultaneously image, track, and deliver stabilized stimuli to the retina. With precise spatial control of our stimuli, we measured the spatial extent of desensitization on the retina. We found that the areas of desensitization extended beyond the local area where the stimulus was delivered. Though larger than the stimulus area, the areas of desensitization were small and sensitivity increased sharply at their borders. Additionally, they were asymmetric with respect to the targeted stimulus location, and desensitization varied among the cones surrounding the adapting stimulus. These characteristics were roughly consistent with the receptive fields of midget retinal ganglion cells at the eccentricities tested (6–10 degrees). Taken together, these observations are consistent with a high level suppression of signals from a low level post-receptoral mechanism with tiled receptive fields, possibly in the retina or lateral geniculate nucleus.
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