Abstract

Cavanagh et al.¹, claim that the equiluminant point can be assessed by adjusting the luminance contrast of a counterphase, flickering chromatic grating to produce "minimal motion" when this grating is paired with a counterphase luminance grating in spatial–temporal quadrature phase. The contours of direction-identification thresholds in L′=ΔL/L, M′=ΔM/M cone space, measured with a 1 cpd moving grating on a 3500 td yellow field, show that luminance and spectrally opponent motion mechanisms are not orthogonal at velocities above 2°/s (2 Hz): a luminance grating (yellow-on-yellow) also stimulates the spectrally opponent motion mechanism, which becomes L-cone-dominated at these frequencies. Quadrature experiments show that the luminance and spectrally opponent mechanisms jointly contribute to motion when stimulated simultaneously. Thus, for the minimal-motion technique to assess the equiluminant point, it is necessary that the "luminance" pedestal grating be not simply a yellow-on-yellow variation, but rather it must be a vector in L′,M′ space that is parallel to the detection contour of the spectrally opponent motion. Such a vector does not stimulate the latter mechanism and does not contribute to "minimal motion." Thus, it is unlikely that the minimal-motion phenomenon determines equiluminance much above 2 Hz.

© 1990 Optical Society of America