Fig. 7.

Annulus-size tuning curves for 2 example V1 cells and 2 example V2 cells. Response of 2 V1 cells (A and B) and 2 V2 cells (C and D) as a function of the inner radius of an annular grating in the far surround (stimulus shown in C). Cells in A and B are the same cells shown in Fig. 2, A and B; C and D are the same cells as in Fig. 2, D and E. The open triangle represents the response to the center-only stimulus. Open square: response to the largest surround-only stimulus. Solid lines represent fits to the data using the thresholded (t)-DOG model (see methods). Arrows indicate the annulus inner radius at suppression onset, used as a measure of far surround size (10.4° in A, 4.3° in B, >12.5° in C, 4.2° in D). Note that in C suppression is already present at the largest annulus inner radius used. Dashed line: mean spontaneous firing rate. The SI measured with the annulus method at high stimulus contrast for each cell was: 31% (A), 61% (B), 40% (C), 23% (D).