Fig. 4.

Bright light reduces surround inhibition of the ganglion cell response. A: schematic of the circular white noise stimulus used to measure spatiotemporal receptive fields of retinal ganglion cells (example ganglion cell morphology overlaid in white). Luminance of each circle was updated every 33 ms according to a random binary sequence. B: space-time plot of an example ganglion cell spatiotemporal receptive field measured with the circular white noise stimulus. Because annulus area increased with eccentricity, the third or fourth annulus typically showed the strongest positive correlation with the cell’s spike response (excitatory center, red). Negative correlations (inhibitory surround, blue) were strongest ~250 µm from the receptive field center. C: width of the receptive field center, defined as the zero crossing of the spatial response profile (w_c; see inset; n = 8). *P = 0.02; t-test, all other P = 0.16–0.54, not significant). D: temporal filters of the receptive field center and surround (peak and trough in the spatial reverse correlogram; + in B) at different light levels (single-cell example; solid lines, center; dotted lines, surround). E: biphasic index of ganglion cell filters (black line; n = 8: 6 OFF, 2 ON). The spatial biphasic index was calculated as the ratio of the peak amplitude of the center and surround filter measured at each light level (see inset in D).