Figure 3. Changes in sensitivity within the receptive field center.

(A) A single stimulus frame used to map sensitivity changes at high resolution, composed of concentric annuli with radii increasing by 50 μm that were modulated independently with 5 % contrast. In the central 200 μm, the stimulus alternated between 16 s of the 5 % low contrast stimulus, and 4 s of a uniform circle that flickered with a 100% Michelson contrast. (B) Normalized spatial sensitivity of an adapting Off cell during L_late, computed as the rms value of the spatiotemporal receptive field at each distance. Because annuli had a different area, unlike a checkerboard stimulus, the sensitivity at each distance was normalized by the annulus area. The vertical dotted line shows the point of zero crossing, defining the receptive field center. (C) Average normalized difference in spatial sensitivity between L_early and L_late for adapting Off cells (left) (n = 7) and the model from Figure 2 (right). The solid vertical line shows the extent of the central circle that experienced high contrast. The dotted vertical line indicates the average boundary of the receptive field center.