REDNESS FROM SHORT-WAVELENGTH-SENSITIVE CONES DOES NOT INDUCE GREENNESS

According to opponent-colors theory, a reddish surround induces greenness in a central test field. Color-appearance measurements verify this with a long-wavelength reddish surround (660 nm) but not with a short-wavelength reddish surround (440 nm). Surprisingly, a short-wavelength reddish surround shifts the appearance of a test toward redness. Four possible explanations are: (1) stray light from the short-wavelength reddish surround falls in the test area; (2) receptoral sensitivity changes over-whelm induced greenness from the surround; (3) a neural process of assimilation, rather than contrast, to the surrounding light; and (4) short-wavelength-sensitive (S) cones do not contribute to induced redness/greenness. Chromatic cancelation experiments confirm the fourth explanation. There was no change in induced redness/greenness when quantal absorption by only S cones in the surround was varied by 30-fold (using tritanopic metamers), even though varying stimulation of S cones strongly affected the color appearance of the surround. The redness induced by a short-wavelength surround is accounted for by opponent chromatic induction mediated by only middle- and long-wavelength-sensitive cones.