Leo M. Hurvich

Some Quantitative Aspects of an Opponent-Colors Theory. I. Chromatic Responses and Spectral Saturation

Saturation discrimination is assumed to be dependent on the ratio of chromatic to achromatic components in the sensory response to a given wavelength. The usual methods of measurement do not, however, permit independent control of the chromatic and achromatic variables. On the basis of an opponent-colors theory of vision, a method is described for measuring directly and separately the spectral distributions of the chromatic components. A series of experiments is reported in which this method was used to obtain measures of the paired chromatic responses associated with the four primary spectral hues. Results are reported for two observers, 1° foveal test field, for an equal brightness spectrum (10 mL), and a neutral state of adaptation (10 mL). The measured chromatic responses, together with achromatic (luminosity) functions measured earlier for the same observers, are used to predict the form of the spectral saturation discrimination function.

Some quantitative aspects of an opponent-colors theory. II. Brightness, saturation, and hue in normal and dichromatic vision.

A quantitative model for an opponent-colors theory of vision is presented that is based on the CIE color mixture data for the standard observer. The model is used to account for spectral brightness, saturation, and hue and some of their associated psychophysical functions in both normal and dichromatic vision. Special attention is given to an account of the Bezold-Brucke hue shift, and to changes in saturation and wavelength discrimination with changes in stimulus luminance.

Theory of brightness and color contrast in human vision

Abstract A theory of induced opponent responses is developed to account for perceived brightness and colour contrast effects. Generalizations from classical contrast experiments are analysed in terms of induced chromatic and achromatic response theory. Functional relations derived from the theoretical statements are compared with experimental data sampled from a variety of matching, scaling and discrimination experiments.

Some quantitative aspects of an opponent-colors theory. III. Changes in brightness, saturation, and hue with chromatic adaptation.

A theoretical model for an opponent-colors theory of vision is used to predict and describe quantitatively changes in the brightness, saturation, and hue of colors with changes in chromatic adaptation. The systematic nature of such changes in color appearance is examined, and comparisons are made between specific theoretical predictions and results of experimental studies of chromatic adaptation.

Some quantitative aspects of an opponent-colors theory. IV. A psychological color specification system.

A system for the numerical specification of colors is developed on the basis of a quantified opponent-colors theory. The derived HBS (hue, brightness, and saturation) system permits the quantitative specification of colors in terms of their primary psychological (perceptual) attributes for various adaptations and illuminations.

The experimental determination of unique green in the spectrum

The notion is gaining currency that observers who are distributed normally with respect to commonly measured indices of color vision, may be bimodally distributed with respect to the spectral locus of unique green. Experimental conditions which can produce such deviations from a normal distribution are explored, and it is concluded that the “bimodality” results reported in the literature may reflect differential chromatic adaptation effects. Experimental conditions which guarantee a neutral state of adaptation yield spectral unique green loci that show no evidence of bimodality.

From Contrast to Assimilation: In Art and in the Eye

The authors, using physiological arguments, discuss the approximate nature of the concept of perceptual object color constancies, which are thought by some to obtain regardless of illumination level and quality. The phenomenon of contrast, so well exemplified by works of Claude Monet and Josef Albers, is cited as evidence of nonconstancy. Experimentally observed response of individual retinal cells to very small light beams is used to support the principle of retinal antagonistic organization as applied in color vision and is extended to spatial hue and lightness contrast. The finding that individual retinal cells have ‘receptive fields’ that differ in size is used to account for the opposite phenomenon of assimilation. The authors direct attention to contemporary and older paintings and graphic works that possess the particularly interesting effect obtained when assimilation is present.

A Psychophysical Study of White. I. Neutral Adaptation

A discussion is presented of the concept white as it is used to describe properties of light, properties of objects, and properties of sensation. The concept can have both practical and theoretical significance only when the psychophysical functions relating the sensation white to the stimulus variables are known. An apparatus and method used to obtain such functions are described. Data are presented for three observers, for a neutral state of adaptation, dark surround, 11.7° test field, and a one-second stimulus duration. White threshold contours are shown which relate the approximate color temperature of the test stimulus and the luminance required to evoke a sensation of absolute white. These contours form the lower boundary of a white sensation area, in which all color temperature-luminance combinations evoke an absolute white sensation for the given observers and experimental conditions.

Theoretical analysis of anomalous trichromatic color vision.

Anomalous trichromatic color systems are examined within the framework of a three variable, bimodal opponent-colors theory. Specific types of anomaly are assumed to be related to specific changes in the normal photoreceptor distributions and to impairments in the normal chromatic response processes. The aberrant color equations, color sensations, and color discriminations of both protanomalous and deuteranomalous observers are shown to be meaningfully related to the postulated, systematically aberrant visual mechanisms.

Spectral Sensitivity of the Fovea. I. Neutral Adaptation

The spectral sensitivity of the 1° fovea of the right eye of two practiced observers was measured at 10 mμ intervals from 400 mμ to 700 mμ for the dark-adapted state and for the bright-adapted (10mL), chromatically neutral state. Ten complete luminosity functions were obtained for each observer for each of the specified adaptations. The data of these experiments are intended to provide controls against which to evaluate luminosity data for different chromatic states. A number of inflections and shoulders are found in the functions for both states of adaptation. Moreover, the functions for both observers are shown to undergo a change in form and a displacement from the bright to the dark-adapted state. These changes in the foveal functions, although small in magnitude, are in the same sense as the familiar “Purkinje shift.” Alternative theoretical explanations of the data are discussed and analyzed.