Abstract
Colour constancy employs the classification and integration of edge signals over large parts of a
scene. However, the properties of the actual physiological processes underlying such large field
computations are little understood. In previous experiments, we found that the early time-course
(0.2 s ^ 5 s) of mid-spectral chromatic adaptation is accelerated by a cortical mechanism that
responds to contrast in the adaptation pattern (Werner et al, 2000 Vision Research 40
1101 ^ 1113). In our new experiments, we investigated the properties of this spatial component of
chromatic adaptation. The pattern (15.4 deg613.2 deg) was presented on a calibrated colour
monitor and consisted of horizontal stripes of different luminances. For the reference condition,
it was achromatic (u 0 0:197, v 0 0:468; Lmean 19:3 cd mÿ2 ). Chromatic adaptation was
measured for the transition from D65 adaptation to a 5 s green adaptation light located in an
equiluminous plane in colour space. The effect of chromatic adaptation was measured by a hue-
cancellation technique, which involved maintaining the achromatic appearance of a central test
patch (2.2 deg62.4 deg). Our results provide evidence for a spatial mechanism of chromatic
adaptation, which responds to the spatial features of the adaptation pattern, namely its spatial frequency and orientation.
