Interaction between Colour and Depth Channels in Transparent Colour Perception

Abstract

Two colours can be perceived at one location on overlapping planes only when the front plane is transparent. This phenomenon suggests that colour information processing is not independent of depth information processing and vice versa. To investigate the interaction between colour and depth channels, we used colour stimuli and binocular parallax to identify the conditions for transparency. Each stimulus, presented on a CRT to one eye, consisted of a centre patch and a surround. Binocular disparity was set so that the centre patch could be seen behind the surround. However, the surround appears to be behind the centre patch when the surround is perceived as an opaque plane. We examined several combinations of basic colours for the centre patch and surround. The surround luminance was constant at 1.0 cd m⁻² and the luminance of the centre was varied. Subjects used the apparent depth of the surround to report whether or not transparency occurred. The results show two types of transparency: ‘bright-centre transparency’ and ‘dark-centre transparency’. We found that the range of centre luminances which yield transparency depends on the combination of centre and surround colours, ie influences of brightness and colour opponency were found. We conclude that there is interaction between colour and depth channels in the visual system.