Temporal integration of stimulus increments under chromatic adaptation: effects of adaptation level, wavelength, and target size.

The threshold-duration functions were determined for a 520-, 570-, or 650-nm test presented upon the various monochromatic backgrounds. The variation of the threshold-duration functions with the background intensity, taken with the 520- or 650-nm test, showed a strong dependence on the background wavelength. This wavelength difference became prominent for the high background intensities: for the bright 570-nm background, partial summation occurred for the duration range from 50 to 200 msec, while such a partial summation effect was very small for the bright 520- and 650-nm background. Test for test-mixture additivity indicated that the longer integration time, obtained for the 520- or 650-nm test with the 570-nm background, was attributed to contribution of the opponent-color process. The elongation of the temporal integration period was found to be affected by the size of the test target. The interrelation among temporal and spatial summation, background intensity, and wavelength could be accounted for by temporal integration of the opponent-color process in addition to that of the cone mechanisms.