Additivity of induced blackness

Abstract

The additivity of induced blackness was tested in conditions of temporal contrast. Two adult observers foveally viewed an inducing field composed of either one of seven variable wavelengths (430-670 nm, 40-nm steps), one of two addend wavelengths (510 and 630 nm), or a combination of one variable wavelength and one addend wavelength for 5 s followed immediately by a broadband (5500-K) reference stimulus of the same size (0.75°) and spatial location as the inducing field. The observers increased the radiance of the inducing field until the reference stimulus appeared completely black. Additivity tests were also obtained with the same wavelength combinations for each observer using heterochromatic flicker photometry (HFP) and direct brightness matching. The additivity results from blackness induction resembled those from HFP, whereas the results from brightness matching showed clear additivity failures of the cancellation type. These findings were also corroborated by additivity tests performed on spatially induced blackness. These data indicate that the perception of blackness is mediated by neural mechanisms that additively combine the input of middle- and long-wave photoreceptors.