Color contrast adaptation has been used to examine properties of color coding in central color mechanisms. Psychophysical researches showed that the adaptation to a field whose color varies along a single axis in color space induces a selective loss in sensitivity to the adapting axis. We examine whether the same contrast adaptation is obtained by visual evoked potentials and whether there are more narrowly tuned cortical mechanisms.

High contrast 1.0 c/deg., horizontal sinusoidal gratings with 2 Hz pattern reversal rates were used for adapting stimuli. The combination of color was chosen from axes within the equiluminant plane. We tested L-M, S-LM axis, and the axes intermediate to the cardinal. Test stimuli were the same as the adapting except were low contrast. After adaptation to a stimulus modulating one direction for 5 minutes, test stimuli along different axes were shown in random order interleaved by 10 sec re-adapting stimulus. Preliminary results showed that the amplitude of response decreased the most along the adapting axis. Latency did not show systematic differences. The selective reduction of amplitude is consistent with the sensitivity loss in psychophysical studies and suggests the existence of narrowly tuned channel intermediate to the cardinal axes.