Modeling spatial contrast sensitivity in responses of primate retinal ganglion cells to natural movies
Fig 7
Analysis of spatial scale of contrast sensitivity.
A: Schematic of the SC model from Fig 2, modified to include spatial stimulus smoothing before the computation of LSC. B: Spatial smoothing analysis for a sample cell in response to white noise. Gray curve shows the SC model performance for different smoothing scales, normalized to performance without smoothing. The optimal scale is obtained by interpolation (black segment). Sample white-noise frames at different smoothing scales are shown on top, with the red outline marking the approximate optimal scale. C: Spatial smoothing analysis for all cells under white-noise (top) and naturalistic-movie (bottom) stimulation, with the region around the peak shown enlarged in the inset with dashed outline and relative model performance shown as percentage improvements over a model without smoothing. Distributions of spatial scales of nonlinear stimulus integration for each cell class under white noise are shown in the inset histograms. The x-axis here corresponds to the range of the red segment of main plot. D: Radially-averaged power spectral density (RAPSD) curves averaged across frames of white noise (left) and of the naturalistic movie (right) for different scales of spatial smoothing. Spatial scale (x-axis) is here defined as the inverse of spatial frequency. Shaded gray areas mark the range of 40–50 μm, matching approximately the range of spatial scales from C. Note that the RAPSD of the non-smoothed white-noise stimulus falls off for small spatial scales because RAPSD curves were here computed based on monitor-pixel resolution and the stimulus was close to white only for scales beyond the length of two stimulus squares. Frame of the stimulus in A taken from an open-source movie licensed under CC BY 3.0 [28].