Changes in field spectral sensitivities of red-, green- and blue-sensitive colour mechanisms obtained on small background fields

When field spectral sensitivities of the red- and green-sensitive colour mechanisms are determined in the presence of a small steady background field (auxiliary conditioning field), spatially coincident with the test field, the resulting curves may be found to be narrowed and shifted away from each other on the wavelength axis. These "sharpened" curves tend to peak at wavelengths of 605 nm and 530 nm respectively. This investigation determines spectral sharpening for variations in the intensity, wavelength, and size of the auxiliary conditioning field, and for variations in the wavelength and duration of the test flash. The following results were obtained. 1. (1) The intensity-wavelength dependence of an auxiliary field that produces a constant spectral sharpening of the red-sensitive mechanism is indistinguishable from the sharpened field spectral sensitivity curve of the green-sensitive mechanism. 2. (2) The wavelengths of the test flash at which maximum spectral sharpening of the red- and green-sensitive mechanisms occurs are 610-620 nm and 530 nm respectively. 3. (3) Spectral sharpening is reduced or eliminated when the test flash has short duration. 4. (4) No spectral sharpening is apparent at moderate-to-high intensities for the blue-sensitive mechanism. 5. (5) The variation of spectral sharpening with auxiliary-field size depends strongly on test-field size. This dependence could be made approximately constant when data were scaled according to cortical magnification factor M. 6. (6) Spectral sharpening is abolished, or severely diminished, when the auxiliary field is presented dichoptically. These findings are considered in relation to an opponent-process theory of colour encoding, the site of the coincident auxiliary-field effect and other data on interactions amongst colour mechanisms. © 1981.