in color vision research, a hypothetical typical human visual system that is described in terms of mathematical functions and equations relating its quantitative visual responses to measurable physical characteristics of light stimuli. The descriptions are therefore psychophysical and used to achieve a shared technical description of the perceptual effects of light stimuli on human observers. The equations that define the standard observer are based on averages of laboratory measurements of the visual responses of human participants to particular light stimuli under particular viewing conditions. See also ideal observer.