The Foveal Visual Representation of the Primate Superior Colliculus

We show that the superior colliculus, classically associated with extra-foveal spatial representations needed for gaze shifts, is highly sensitive to visual input impinging on the fovea

Chih-Yang Chen; Klaus-Peter Hoffmann; Claudia Distler; Ziad M. Hafed

2019

Scholarcy highlights

  • A tiny portion of our retina, the fovea, contains the highest photoreceptor density while, at the same time, commanding large neural tissue magnification as signals traverse from retina to lateral geniculate nucleus and primary visual cortex
  • Despite the importance of foveal visual processing, and despite the suitability of primates for investigating it, studies of foveal visual mechanisms have become increasingly rare in the past 3 or 4 decades. This is primarily due to challenges associated with studying foveal vision: foveal retinal ganglion cells often have response fields that are the size of single photoreceptors ; even tiny fixational eye movements can displace images away from RFs, and this can affect downstream areas that spatially pool retinal ganglion cell information
  • We carefully controlled for image shifts caused by fixational eye movements
  • We found a the following equations, based on, relating tissue space to remarkable difference: what the original model predicts as the visual coordinates: 5-degree eccentricity line in neural tissue is in reality only the pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi ! X = Bxloge R2 + 2ARcosðqÞ + A2
  • For neurons no. 2 and no. 4 from Figure 1, plot- An additional functional consequence of large foveal magnificating their RF images in neural tissue space revealed that the area tion is that small eye movements can, by virtue of moving retinal occupied in anatomical space was greater than five-fold the area images, cause substantial variations in superior colliculus neural activity
  • The primate superior colliculus contains a high-fidelity visual representation, with large foveal magnification, perfectly suited for active visuomotor control and perception

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