Lateral inhibition in human colour mechanisms.

1. The spatial properties of human colour mechanisms were explored by measuring contrast thresholds for sine-wave gratings, under conditions of intense chromatic adaptation, from 0.25 to 12 cycles/degree.2. With adapting colours that tend to isolate the red-, green-, and blue-sensitive spatial responses, all three results differ markedly from each other and from the neutral grating sensitivity. The green mechanism is much more sensitive than the others, the blue, much less. In all cases, the contrast sensitivity decreases at low spatial frequencies, which is typically the result of lateral inhibition. This low-frequency inhibition effect is greatest for the unadapted case; it diminishes significantly but does not vanish when the red or green mechanism is isolated.4. These results imply that there is spatial inhibition both between and within the red and green mechanisms. Chromatic adaptation can eliminate the former but not the latter.