The independence of the temporal integration properties of individual chromatic mechanisms in the human eye.

1. Since it has been shown by Stiles that the adaptive states of the primary chromatic (pi) mechanisms of the human eye vary independently and since recent theories of visual function have postulated an intimate relation between sensitivity and the temporal characteristics of the retinal response, it is asked whether the temporal integration properties of the eye depend upon the state of adaptation of the retina as a whole or vary independently for each of the chromatic mechanisms.2. It is found that the critical duration, or limit of time-intensity reciprocity, for the detection of monochromatic increments presented on monochromatic background fields depends only upon the adaptive state of the individual pi mechanism mediating the detection. Our results support the hypothesis that each chromatic mechanism has its own automatic gain control.3. At both dark-adapted and asymptotic levels the critical durations for the short wave-length mechanisms appear to be greater than those for pi(4) and pi(5).4. When 500 nm test flashes are presented on 600 nm adaptation fields, critical durations increase at high background intensities. This anomaly adds further support to the hypothesis that the critical durations of different chromatic mechanisms vary independently, since 500 nm flashes are probably detected by pi(1), rather than by pi(4), when presented on long wave-length adaptation fields of high energy.5. Our findings provide partial support for the suggestion that the Fechner-Benham subjective colours are due to differences in the time constants of the different colour mechanisms.6. It is concluded that the critical duration is principally determined at a very distal stage in the visual system before interactions occur between chromatic mechanisms.