Controversy in the past has centred round the possibility of pro- ducing binocular colour mixture: very little interest has been shown in explaining either it or binocular rivalry.

Haldat gave an explanation which was based on his theory of stereoscopic vision.

Binocular colour mixture he explained in the same way as single vision with two eyes.

An object appears single although it stimulates each retina and so evokes two sensations, because touch has shown that it is really single.

Double objects would therefore appear single when, their impressions falling separately and simultaneously on corresponding points of the retinae, the same sensations were experienced as excited the idea of a single object.