Abstract
Previous experiments indicated that edge-dependent, double-opponent neurons are involved in the color perception of patterns (Nunez et al., 2017). These earlier experiments measured perceptual scaling of color saturation by human observers, for equiluminant red squares on a gray background and also red-gray checkerboards of the same size and space-averaged cone contrast. While the red patterns evoked responses primarily from the Parvocellular system, we wanted to determine whether or not double-opponent neurons driven by signals from the parallel Koniocellular pathway are also involved in color-pattern perception. Therefore, we modified our ratings experiments, (pattern-onset, square-wave modulated checkerboards [0.5s on, off until a rating is recorded]), with color contrasts varying along the L-M and S-cone-isolating directions in color space for N=7 observers. Perceived color saturation increased with cone contrast for both stimulus patterns and for both color directions. For both color directions, checkerboard stimuli consistently produced larger color saturation than color squares of the same space-averaged cone contrast. Because V1 is a bottleneck for color perception, we must consider the only two classes of color-responsive neurons in V1: single- and double-opponent neurons. The spatially integrative responses of single-opponent neurons would have produced the same saturation for checkerboards and color squares matched for space-averaged cone contrast. The larger saturation of checkerboards must have been caused by the contribution from a neural mechanism that responded to the checks themselves, namely, double-opponent cells. Therefore, we conclude that double-opponent neurons are involved in the perception of color in color patterns for both the Parvocellular and Koniocellular systems.
This research was supported by grant PAC-1555773 from the National Science Foundation.