Abstract

Hue and color brightness difference thresholds were measured by the method of adjustment at thirty wavelengths. These wavelengths were tested in ascending and descending orders on successive days. As a result, on half of the trials each wavelength was preceded by a shorter wavelength, on the other trials preceded by a longer one. The hue evoked by each wavelength was measured systematically. The hue appearance of each wavelength was found to be altered by the order in which the wavelengths were tested. These hue changes did not alter the hue discrimination function: i.e., hue difference thresholds were largest around 530 nm regardless of whether that wavelength appeared to be green on descending wavelength days or yellow-green on ascending wavelength days. Hue discrimination depends on wavelength and not on hue. On the other hand, the color brightness discrimination function tended to shift with wavelength as the appearance of those wavelengths shifted in hue: i.e., when testing from 425 to 625 nm, brightness difference thresholds reached a maximum at 555 nm which was reported as yellow; when testing from 655 to 425 nm, this peak shifted to 575 nm while yellow shifted to 580 nm. Color brightness discrimination depends mostly on hue not wavelength. These results suggest that (1) color appearance and color discrimination are mediated by separate mechanisms; (2) hue discrimination is mediated by mechanisms that are proximal to the receptors; (3) color brightness discrimination is mediated more centrally than hue discrimination.

© 1986 Optical Society of America