Analysis of human color mechanisms using sinusoidal spectral power distributions.

We examined the effects of probing human color mechanisms using sinusoidal spectral power distributions (SPD's) varying in frequency (i.e., from 0.1 to 5.0 cycles/300 nm for a constant starting phase) and phase (i.e., from 0 to 360 deg for a fixed frequency of 1 cycle/300 nm) through computer simulation using several color models. Predicted modulation sensitivity functions (MSF's) in spectral frequency and phase differ among the models and indicate that measurements of the minimum amplitudes necessary to detect sinusoidal SPD's would be useful for distinguishing among theories of color vision. MSF's obtained from similar analyses of dichromats' color mechanisms reveal characteristic patterns of modulation sensitivities and suggest that such measures could serve to distinguish type and degree of color-vision defect. Some implications based on sinusoidal approximations to illuminant and reflectance spectra are discussed along with more general considerations regarding sine-wave SPD's as a probe for mechanisms of color vision.

Remarks on signal-processing explanations of the trichromacy of vision.

We present criticism of signal-processing arguments recently used to explain the trichromacy of color vision. In particular, we note that illuminant spectral power distributions (SPD's) can be metameric even when the signal-processing arguments state that trichromatic vision represents such SPD's without ambiguity. Being statistical in nature, these arguments need not apply to each individual SPD; however, further use of the arguments calls for attributing them to some ensemble of SPD's and then testing whether the ensemble satisfies the underlying statistical assumptions.

Detection and recognition of visual targets.

To aid the development of detection-based interpretations of visual resolution, we evaluated theorems that (1) relate observers' performance in detection of a single target to that in 1-of-m signal detection and (2) predict recognition performance from measured performance at 1-of-m detection. These theorems require that the sensory effects of the stimuli be continuous and that the m signals be equally detectable and mutually orthogonal. To evaluate the theorems, we tested observers in simple detection, 1-of-m detection, and recognition of Landolt C targets and compared predicted and observed performance. Predictions of 1-of-m detection performance from that for simple detection and predictions of recognition from the 1-of-m receiver operating characteristic (ROC) were both accurate to within 0.03 in P(A). In addition, predictions of recognition based on the 1-of-m ROC predicted from simple detection were generally accurate. Thus, under restricted experimental conditions, recognition is determined completely by that for simple detection.

Computerized analysis of the Farnsworth-Munsell 100-Hue test.

The method proposed by Farnsworth for scoring the 100-Hue test is reviewed, and measures of the orientation and strength of the error axis are proposed. The error axis and its magnitude are determined by the phase and amplitude, respectively, of the best-fit sinusoid to the function that results from Kitahara's transformation of the subject's arrangement of the colors. In addition, a computer program, written in BASIC, that scores the 100-Hue test according to those methods is described, and a listing of that program is provided in the Appendix.

Post-receptor chromatic mechanisms revealed by flickering vs fused adaptation.

For both normals and dichromats, adaptation to certain pairs of alternating monochromatic caused reduced sensitivity for detection of some test wavelengths when compared to sensitivity losses caused by adaptation to the fused (supra-CFF) sums of the same lights. Since the two adaptation conditions caused equivalent photopigment depletion, and since sensitivities to some wavelengths did not differ between conditions, the effects are ascribed to post-receptor adaptation. Such post-receptor effects were not obtained when adapting wavelengths did not straddle the presumed "crosspoints" of opponent-colors mechanisms, and, when only one opponent mechanism was adapted, effects were absent for test wavelengths at the crosspoint of that mechanism. For the red vs green system, increasing the intensities of adapting wavelengths from 2.2 to 5.5 log td did not appreciably increase the magnitudes of postreceptor effects. Quantitative accounts for the results are derived from a vector model for color vision. The results provide general support for opponent-colors interpretations of normal and dichromatic vision and suggest that the flicker/fused adaptation paradigm is a useful tool for probing postreceptor mechanisms of vision.

Vector model for normal and dichromatic color vision.

The inclusion of cone mechanisms in a slightly revised version of an earlier model allows accounts of phenomena that involve receptor effects as well as dichromatic color vision. Intensity-dependent parameters that stimulate the adaptation of receptors and opponent and nonopponent mechanisms are varied to predict a wide range of data for both normals and dichromats, including: (i) color matching; (ii) the approximate apparent hue and saturation of the spectrum; (iii) foveal spectral sensitivities obtained by flicker photometry and by detection in the dark and under conditions of achromatic or chromatic adaptation; (iv) heterochromatic additivity failures in the dark-adapted and chromatically adapted eye; (v) approximate differences between brightness and luminance; and, (vi) color and wavelength discrimination under varying adaptation conditions.