Concealed colour opponency in ganglion cells of the rhesus monkey retina

Criteria for distinguishing colour-opponent from spectrally non-opponent cells and identifying colour-opponent subtypes on the basis of the cone inputs they receive, have been examined in ganglion cells of the macaque retina using threshold and suprathreshold stimuli, with and without chromatic adaptation. 2. Criteria based on suprathreshold responses were found to be insufficient for distinguishing between opponent and non-opponent cells in one-third of the sample. Criteria based on a 560 nm neutral point were found to be insufficient for distinguishing between colour-opponent subtypes in one-half of the remaining cells. 3. The neutral point of colour-opponent ganglion cells varies with the geometry and intensity of the stimulus, as well as with the amount of centre-surround interaction and the receptive-field location of a cell. As a result, the neutral point is often an ambiguous criterion for identifying colour-opponent subtypes on the basis of their cone inputs. 4. About one third of the colour-opponent ganglion cells did not show colour opponency in the presence of neutral backgrounds, and only revealed this behaviour in the presence of chromatic adaptation (concealed colour opponency). 5. The proportion of these concealed colour-opponent cells increased towards the peripheral areas of the retina.