Perception of blackness.

We sought to measure the mechanisms underlying the perception of blackness in the following way. A central spot (45') of fixed luminance was surrounded by a dark ring (7.5'), and surrounding all was an annular zone (30') of light. This stimulus was presented in Maxwellian view for 0.5 sec every 3 sec. The radiance of the annulus required to make the central area (spot and ring) appear uniformly black was measured for different wavelengths (440-660 nm) of the annulus. These measurements were made for test spots that were either broadband or of wavelength 480, 500, 580, or 660 nm. In all conditions the measured spectral efficiency of induced blackness matched the inverse of the V lambda function. Using the same stimulus, we have also measured increment-threshold functions. For a fixed luminance of the spot, the radiance of the surrounding annulus required to bring the central spot to threshold was measured. These increment-threshold functions do not match the V lambda or blackness functions. Our results show that induced blackness is inversely related to the luminous efficiency function and that the spectral efficiency of induced blackness is distinct from the increment-threshold function measured under these conditions. Furthermore, blackness appears to be independent of the wavelengths of the inducing annulus as well as of the central spot. Thus these results link induced blackness to the luminance pathway and argue against the involvement of the chromatic pathways in the perception of blackness.