Figure 8.

Two measures from the response as a function of contrast were used as tuning parameters in the clustering procedure: contrast threshold (cTh) and the contrast where the response reached half the maximum response (c50). Cluster designation as in Figure 5. A, C1 has neurons with relatively low cTh and c50, whereas neurons in C2 are intermediate in their contrast sensitivity. B, C3 and C4 have overlapping cThs and c50s but are somewhat less sensitive than C1. C, Neurons in the direction-selective cluster (blue triangles) are relatively insensitive to contrast. D, Neurons in C5 and C6 have high cThs and c50, making the clusters stand out as being contrast insensitive. E, One cluster is intermediate in contrast sensitivity (magenta crosses), another insensitive (cyan triangles). The smaller clusters are detailed in Figure 5C, E.