title: Cardinal axes are not independent in color discrimination.
abstract: We measured chromatic discrimination under conditions where the target fields could be distinguished only by the ratio of excitation of the long- (L) and middle-wavelength (M) cones. The excitation level of the short-wavelength (S) cones was varied in the experiments, although for any given measurement the S-cone excitation was common to the two target fields and could not be directly used for discrimination. Adaptation was maintained by a steady neutral background metameric to Illuminant D65. Thresholds varied substantially and systematically with the S-cone level of the target probes, but in a complex way: when the ratio of L:M cone excitation was low, an increase in S-cone excitation reduced the thresholds, but when the L:M ratio was higher, an increase in S-cone excitation raised the thresholds. To account for the pattern of results, we postulate a neural channel that draws synergistic inputs from L and S cones and an opposed input from M cones. The proposed channel has a compressive response function and is most sensitive at the point set by the steady background.
authors.affiliation: Laboratory of Visual Physiology, I. P. Pavlov Institute of Physiology, Nab. Makarova 6, St. Petersburg 199034, Russia. mvd1000@cam.ac.uk
authors.forename: Marina V
authors.initials: MV
authors.lastname: Danilova
authors.forename: John D
authors.initials: JD
authors.lastname: Mollon
mesh_terms: D003116:Color; D003118:Color Perception / Q000502:physiology*; D004192:Discrimination, Psychological / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D011601:Psychophysics; D011930:Reaction Time / Q000502:physiology; D017949:Retinal Cone Photoreceptor Cells / Q000166:cytology; D012165:Retinal Ganglion Cells / Q000502:physiology