The foveal increment threshold for a 425 nm test flash upon monochromatic and bi-chromatic fields exhibits four distinct features: 1. (1) super-additivity of the effects of approximately π1 equated long- and short-wavelength fields; 2. (2) upward deviation of the threshold from the Weber line on bright bluish fields; 3. (3) cancellative sub-additivity of long- and short-wavelength fields whose mixture is approximately in blue/yellow equilibrium; 4. (4) the "limited conditioning effect" of long-wavelength fields, i.e. the π3 plateau. A one-pathway, "two-site" theory proposed by Pugh and Mollon, in which the adaptation at the first site is controlled by the short-wavelength cones alone, and the second site is chromatically opponent, can give a good account of these features. We have investigated the relationship of the opponent site in the π1 π3 pathway to the site of blue/yellow hue cancellation. We measured blue/yellow equilibria for continuously viewed, 10° fields composed of mixtures of a short-wavelength and a long-wavelength component; increment thresholds for a 425 nm flash were then measured upon these and other field mixtures. Lights in blue/yellow equilibrium were found always to yield minimum second-site adaptation in the π1 π3 pathway.
ASJC Scopus subject areas
- Sensory Systems