Abstract

"Indiscriminability action spectra" of the red/green opponent channel can be measured by using a foveally presented 500 ms raised cosine without spatial edges. These spectra represent lights that are rendered indiscriminable at a cone-antagonistic locus. I found that mid-waveand long-wave low-frequency stimuli falling on the same contour, when presented simultaneously on an intense 578 nm adapting field, cancel the "green" and "red" sensations, respectively, elicited by each. That is, the isocancellation contours of the red/green channel are identical to the indiscriminability spectra. Also, using the low-frequency stimulus, I isolated a short-wave mechanism that codes a single "violet" both at and above threshold. Lights between 400 and 489 nm, which fall on the same indiscriminability contour up to 2 log units suprathreshold, are indiscriminable. This single "violet" is distinct from a single "blue" elicited by a second short-wave mechanism whose sensitivity is suppressed by a 578 nm adapting field. This mechanism is manifestly opponent since the color it codes is cancelled by an appropriate yellow low-frequency light.

© 1990 Optical Society of America