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Chih-Yang Chen, Ziad M. Hafed; Spatial frequency tuning characteristics of primate superior colliculus neurons. Journal of Vision 2014;14(10):1410. doi: 10.1167/14.10.1410.
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© ARVO (1962-2015); The Authors (2016-present)
Superior colliculus (SC) receives various visual inputs including from retina, LGN, and V1. Each of these areas has different spatial frequency (SF) tuning characteristics: retinal output and LGN neurons are predominantly low-pass and tuned for low SF's, whereas V1 neurons can be band-pass. However, collicular SF tuning properties in primates are completely unknown. Here, we characterized these properties. We recorded activity from 50 neurons of one monkey fixating a white spot over a gray background. Inside a neuron's response field (RF), a high-contrast, vertical Gabor grating having one of five SF's (0.56, 1.11, 2.22, 4.44, 11.11 cpd) appeared. We measured peak neuronal activity 30-150 ms after stimulus onset and divided neurons based on their preferred retinotopic eccentricity. We characterized visual (V) and visual-motor (VM) SC neurons, and we excluded trials in which stimulus onset occurred <100 ms from microsaccades, to avoid peri-microsaccadic modulations in activity. All neurons (17 V; 33 VM) showed low-pass characteristics, but foveal neurons had slightly peaked tuning curves. Neurons with RF centers between 0.6 and 3 deg preferred SF's up to 4.44 cpd. Slightly more eccentric neurons (<8.5 deg) were most responsive for up to 1.11 cpd. The remaining neurons (<16 deg in our population) only preferred 0.56 cpd and sharply reduced their activity for all other SF's. V and VM neurons behaved similarly, but the visual response to preferred SF's was ~42% lower in VM than in V neurons. We also analyzed visual burst latency. Interestingly, this latency increased progressively with SF even for neurons that preferred higher than the lowest SF. Thus, SC shows clear SF tuning, but this tuning appears different from V1. Besides clarifying SC visual properties, this observation is interesting because it could potentially explain visual performance changes in V1-lesioned 'blindsight' patients, for whom the collicular visual pathway is presumably important.
Meeting abstract presented at VSS 2014
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