Adaptation and the Ives effect.

The Ives effect is the discrepancy between photometric matches made by direct comparison and those made by flicker. When white is used as a standard stimulus, the discrepancy appears to be related to the saturation of the test stimulus. The two methods of photometry involve differences in adaptation. In flicker, the two patches of color are applied to the same retinal area alternately, and the retina becomes adapted to a mixture of the two. In direct comparison, the two colors are applied to separate areas of the retina, each of which becomes adapted to the color falling on it. In this study the state of adaptation is controlled by reversing the bipartite pattern from right to left from reading to reading so that each part of the retina becomes adapted to a mixture of the two colors the same as in flicker. This reversal decreases the Ives effect to an almost negligible amount, indicating that adaptation is a major cause of the effect. Data are also presented for use of yellow and blue standards instead of white.