SHORT-WAVE CONE SIGNAL IN THE RED-GREEN DETECTION MECHANISM

Previous work shows that the red-green (RG) detection mechanism is hig hly sensitive, responding to equal and opposite long-wave (L) and midd le-wave (M) cone contrast signals, This mechanism mediates red-green h ue judgements under many conditions, We show that the RG detection mec hanism also receives a weak input from the short-wave (S) cones that s upports the L signal and equally opposes M, This was demonstrated with a pedestal paradigm, in which weak S cone flicker facilitates discrim ination and detection of red-green flicker, Also, a near-threshold +S cone flash facilitates detection of red flashes and inhibits green fla shes, and a near-threshold -S cone flash facilitates detection of gree n flashes and inhibits red flashes. The S contrast weight in RG is sma ll relative to the L and M contrast weights, However, a comparison of our results with other studies suggests that the strength of the absol ute S cone contrast contribution to the RG detection mechanism is 1/4 to 1/3 the strength of the S contribution to the blue-yellow (BY) dete ction mechanism, Thus, the S weight in RG is a significant fraction of the S weight in BY, This has important implications for the 'cardinal ' color mechanisms, for it predicts that for detection or discriminati on, the mechanisms limiting performance do not lie on orthogonal M-L a nd S axes within the equiluminant color plane. (C) 1998 Elsevier Scien ce Ltd. All rights reserved.