Figure 7.
The F2 component of parasol cells, like the F1, is sensitive to a range of contrasts and temporal frequencies. A, B, F1 and F2 responses from the same cell measured with drifting and contrast-reversing gratings of optimal spatial frequency, respectively, as a function of temporal frequency ranging from 0.61 to 31.51 Hz at 3.125, 6.25, 12.5, 25, 50, 75, and 100% contrast. C, Mean F1 (gray solid circles, n = 5) and F2 (open circles, n = 6) temporal modulation transfer functions at 50% contrast for optimal spatial frequency (error bars indicate 1 SD). The average peak response was 13 Hz (n = 5) for the F1, and 11 Hz (n = 6) for the F2. D, Mean F1 (gray solid circles) and F2 (open circles) contrast–response functions with Naka–Rushton fits (as described in A with data collected at 10.5 Hz; error bars indicate 1 SD). Curves are characterized by their contrast gain defined as the maximal response in impulses per second divided by the semisaturation constant (a/b). E, Histogram of individual contrast gain values for responses in D (F1, gray bars, n = 12; F2, open bars, n = 12). F, Average F1 (solid circles, n = 5) and F2 (open circles, n = 6) contrast gain values as a function of temporal frequency (error bars indicate 1 SD). The z-axis is spatial frequency, denoting the average optimal spatial frequency used to collect the F1 and F2 contrast gain values. The average optimal F2 spatial frequency is ∼10 times that of the average optimal F1 spatial frequency and well beyond its spatial frequency resolution.