Colour vision can contribute to fast corrections of arm movements.

Can chromatic information be used for the fast on-line control of action? In order to find out we asked subjects to tap a red square as quickly as possible. In half of the trials the red square's position changed as soon as the subject's hand started to move. We examined how quickly subjects could adjust their movements to this change. In half of the trials there was also a green square of the same luminance as the red one. If there was a green square, and the red square's position changed, the change consisted of the two squares exchanging places, so that all that really changed was the squares' colours. In such cases subjects could not have adjusted their movements without having analysed the colour. Nevertheless, subjects could respond adequately within as little as 120 ms. This was even so if the squares' luminances changed considerably at the moment that the subject's hand started to move. Thus, chromatic information can be used for the fast on-line control of action.