Abstract
There are two hypothesis of mechanism of chromatic afterimage. One is the bleaching theory which is proposed that the cause of this phenomenon is bleaching of retinal cone photochemical pigments. And the other idea is that afterimage is caused by adaptation of higher neural mechanisms which are not only affected by three cone factors. To examine these hypothesis, the effect of background colour were measured by the blank rotation method which were composed of circular arranged inducers and a blank region which are rotating circularly and yield constant chromatic afterimage. The lines between the colour of inducers and that of chromatic afterimages which were matched by subjects crossed each other at one point on the chromaticity diagram, and the standard deviation within and between subjects are very small. These facts are thought to show that the measurement was very precise and accurate. This crossing point between inducers and chromatic afterimage colours is regard to be some kind of neutral point of our chromatic afterimage mechanism. And the variation of background colour where the experimental inducers were presented affected to this crossing point, i.e. the crossing point changed to be close to the background colour. As bleaching of cone photochemical pigments are depend on the direct light from visual target, these results reported here suggested that the mechanism of chromatic afterimage are not only bleaching of photochemical pigments but also the adaptation of more higher neural mechanisms.