Systematics of human photopic spectral sensitivity

Abstract

At first glance the various patterns of human photopic spectral sensitivity reported in the literature seem to be an inhomogeneous and partly controversial crowd, even when focusing on psychophysical increment sensitivity. However, a closer look at the conditions of evaluation permits some insight into rules, according to which photopic luminosity varies: (i) The luminosity curve tends to have a smooth shape at short exposure times and high stimulus frequencies, a knowledge already originating from the old work of v. Kries, when colour extinguishing procedures were developed to avoid the observer’s conflict between luminosity and hue. The common underlying process consists of bypassing the colour antagonistic mechanisms. Observation at low levels of adaptation likewise favours the synergistic mode of processing receptoral signals. (ii) In contrast, conditions of long exposure, large test field area, and high levels of adaptation promote colour antagonistic processing of receptoral signals, leading to the three-peaked pattern of spectral luminosity. Once the pattern of the three-peaked sensitivity function is achieved, no further increase of either stimulus duration or diameter has significant bearing on the spectral luminosity function, the shape and level of which then is subject to only minor alterations. (iii) Stimulus displacement towards the retinal periphery increases the demands (e.g., the spatial demands) of the three peaked sensitivity function which, in general, can be achieved at any retinal location. (iv) Beyond doubt, the blue system’s contribution to luminosity does exist. However, it is a particularly delicate one, being reduced or even abolished by downsizing stimulus diameter, shortening stimulus duration, or increasing stimulus frequency. With regard to the slowness and scarceness of short-wave retinal elements, these features no more remain peculiarities. KeywordsSpectral SensitivityColour VisionLuminosity FunctionColour ConstancyColour Vision DeficiencyThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.