A–C, Responses to +50% (gray) and −50% (black) contrast steps in three different cells types at two different luminance levels (solid lines represent the average response, shaded areas represent the s.e.m, number of cells indicated in parentheses in D). D, Rectification index for each cell type at 0.5 R*/rod/s and 100 R*/rod/s (see Experimental Procedures). Error bars represent s.e.m. Paired t-tests were used to compare within-cell data (AII and RGC recordings) and an unpaired t-test was used to compare cone bipolar cells that were recorded at 0.5 R*/rod/s or 100 R*/rod/s and to compare cone bipolar cells and RGCs (*, * and ** represent p-values of < 0.05, 0.01 and 0.001, respectively). AII amacine cell and type 6 cone bipolar cell recordings (A,B,D) are from slice preparations; On alpha RGC recordings (C,D) are from whole mount preparations.