Chromatic adaptation

Adjustment of visual responses to the spectral statistics of prevailing stimulation. Changes in gain or reference levels can partially stabilize color judgments despite different illumination or receptor signals. Adaptation is an explanatory mechanism to test; similarity on a color test does not uniquely identify its neural implementation.

A diagonal model applying gains $g_j$ to cone signals. If a change transforms every relevant catch as $Q_j\mapsto k_j{Q}_j$, gains $g_j\mapsto g_j/k_j$ preserve the normalized outputs exactly. A general illuminant change need not produce the same channelwise factors for every surface, so exact cancellation is conditional.

Changes following exposure to variation around a mean color or luminance. Holding the mean input fixed helps distinguish adaptation to variation from a simple account based on changed average cone catch, while receptor nonlinearities and task factors still require controls.