Figure 13.

Changes in spatial frequency have a limited effect on the temporal phase of visual responses to drifting gratings. (a, c, e) Average phase shifts for spatial frequency, contrast, and phase measured with drifting luminance gratings (units are fractions of a cycle). (b)(d, f) Average phase shifts for spatial frequency, contrast, and phase measured with drifting equiluminant gratings. Notice that not all cortical simple cells could be measured with all stimulus conditions. Measurements of spatial frequency were obtained in 72 cells, luminance contrast in 31 cells and grating size in 53 cells. Measurements with equiluminant gratings were restricted to a small population of simple cells that were color responsive (10 for spatial frequency, 3 for color contrast, and 5 for grating size). Error bars show standard errors of the mean.