Spectral efficiency of blackness induction.

The spectral efficiency of blackness induction was measured in three normal trichromatic observers and in one deuteranomalous observer. The psychophysical task was to adjust the radiance of a monochromatic 60-120' annulus until a 45' central broadband field just turned black and its contour became indiscriminable from a dark surrounding gap that separated it from the annulus. The reciprocal of the radiance required to induce blackness with annulus wavelengths between 420 and 680 nm was used to define a spectral-efficiency function for the blackness component of the achromatic process. For each observer, the shape of this blackness-sensitivity function agreed with the spectral-efficiency function based on heterochromatic flicker photometry when measured with the same 60-120' annulus. Both of these functions matched the Commission Internationale de l'Eclairage V lambda function except at short wavelengths. Ancillary measurements showed that the latter difference in sensitivity can be ascribed to nonuniformities of preretinal absorption, since the annular field excluded the central 60' of the fovea. Thus our evidence indicates that, at least to a good first approximation, induced blackness is inversely related to the spectral-luminosity function. These findings are consistent with a model that separates the achromatic and the chromatic pathways.