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Antony Morland, Barbar Molz, Rebecca Lowndes, Andre Gouws, Heidi Baseler; Population receptive fields in V1 enlarge as luminance is reduced from photopic to scotopic levels. Journal of Vision 2018;18(10):577. doi: 10.1167/18.10.577.
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© ARVO (1962-2015); The Authors (2016-present)
Under photopic conditions visual information is processed at the retinal level by cone photoreceptors while under scotopic light conditions visual signals are solely conveyed by rod photoreceptors. There is a markedly different distribution of rods and cones across the retina, most notably in the central fovea, where only cones are found. Spatial resolution is lower under scotopic compared to photopic conditions even at eccentricities at which there are greater rods than cones. This largely reflects the greater spatial summation in the rod compared to cone system. We sought to examine whether the increased spatial integration that is a feature of the rod pathway is reflected in changes in population receptive field characteristics in primary visual cortex. To this end we employed established population receptive field mapping techniques under four different luminances – two high light levels, 600 and 20 cdm-2, at which cones operate and two lower light levels 0.01 and 0.002 cdm-2, at which only rods operate. We then evaluated the population receptive field size in V1's representation of ~5-8deg eccentricity. This representation can be driven by either rods or cones. We found a strong effect of light level on population receptive field size, with the lower, scotopic light levels yielding larger estimates of size than those obtained at light levels that drive cones. However, there was no significant change in population receptive field size for the two of luminance levels used to drive cones or for the two used to drive rods. Our finding is in line with our hypothesis that neurons integrate information over larger areas of the visual field under scotopic compared to bright light conditions, highlighting the differences in spatial integration of the rod and cone pathways.
Meeting abstract presented at VSS 2018
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