Abstract

The human photopic luminous efficiency function, the basis of photopic photometry for over 50 years, may be derived from several psychophysical tasks. These tasks are sometimes assumed to tap a "luminance channel" in the visual system, but the physiological identity of this channel has been controversial. The physiological basis of two photometric tasks will be discussed. For flicker photometry, there is strong evidence that cells of the phasic, magnocellular system of the primate visual pathway form the substrate. Not only can photometric properties, such as additivity and transitivity, be demonstrated in this pathway, but also odd psychophysical effects, such as that seen when the relative phase of two flickering lights changes, find a precise correlation in the responses of these cells. This makes it unlikely that cells of the parvocellular system contribute to this task. For another photometric task, the minimally distinct border, evidence for M-pathway cells as the physiological substrate is also compelling, implying that this pathway is a major contributor to form vision. It is parsimonious to suppose that the M-pathway is involved in other photometric tasks, such as resolution photometry.

© 1990 Optical Society of America