1. It has been hypothesized, but not verified empirically, that the control of human ocular accommodation is mediated by either the red-green or yellow-blue colour channels. Our goal was to determine experimentally whether the red-green channel by itself could influence the accommodative response. 2. To find out, we isolated the red-green channel through chromatic bandpass filtering and measured accommodation under dynamic and static conditions. The effect of this filtering was to modulate the red-green channel without disturbing either the yellow-blue or luminance channels. 3. Accommodative gain (ratio of response to stimulus amplitude) declined monotonically with decreasing bandwidth under dynamic conditions. Because the outputs of both the luminance and yellow-blue colour channels did not vary with bandwidth, the only explanation is that the red-green opponent process was responsible for the effect. 4. Under static conditions, however, accommodation was independent of bandwidth. This may be attributable to the decreased sensitivity to chromatic contrast that occurs at low temporal frequencies.
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