Colour signals from incremental and decremental light stimuli

Abstract

A red stimulus ( ΔR) was presented in the centre of a red background (R), either as an increment ( ΔR > 0), a decrement ( ΔR < 0), or a pseudo-increment ( ΔR = 0, but surrounded by a narrow decremental border of varying depth. A green cancellation stimulus ( ΔG). coincident with ΔR, was adjusted until the test field looked neither reddish nor greenish, and thus yielded a measure for the strength of the red colour signal at the test field locus. The results are consistent with the hypothesis that chromatic vision is subserved by (colour specific) difference signals, which arise from incremental discontinuities in the retinal image profile. Decrementai inputs seem to feed only into the achromatic system, generating a blackness signal.