Robert M. Boynton

Chromaticity diagram showing cone excitation by stimuli of equal luminance.

In a space where Cartesian coordinates represent the excitations of the three cone types involved in color vision, a plane of constant luminance provides a chromaticity diagram in which excitation of each cone type (at constant luminance) is represented by a linear scale (horizontal or vertical), and in which the center-of-gravity rule applies with weights proportional to luminance.

Bezold–Brücke Hue Shift Measured by Color-Naming Technique*

Three experiments on the Bezold–Brucke phenomenon (change in the hue of spectral colors caused by change in field luminance) are reported. The first is an exact replication of Purdy’s classic experiment, where the shift between 100 and 1000 trolands is investigated by direct matching in a steadily presented bipartite field. The second is a modification of Purdy’s experiment where the observer is asked to match on the basis of 300-msec flashes of the bipartite field. The third is an experiment where no matches are required, but where the observer is asked to judge the hue of a flashing stimulus using a forced-choice color-naming technique. The results of the three experiments are compared: differences are discussed in terms of viewing time and simultaneous contrast.

Interactions among chromatic mechanisms as inferred from positive and negative increment thresholds

Abstract When two flashes of light are delivered to the light-adapted eye at the same time and place, their combined increment threshold provides evidence about (a) integration or cancellation of energy within receptors, (b) physiological summation and inhibition of receptor outputs, and (c) probability summation. These relations are examined using high-energy positive and negative red flashes (630 nm) paired with positive flashes of other wavelengths. All of these phenomena are found to occur. A high degree of complex interaction among receptors is implied by the results.

Eye-Movement Responses to Step and Pulse-Step Stimuli*

A spot of light is presented to an observer who tracks its movement visually, doing so as quickly and accurately as possible. The positions of the eye are continuously recorded so that direction and magnitude of eye movements as a function of time can be assessed. Without warning, the target spot steps from its resting position, moving 6° horizontally to one side, followed after a time W by a 12° step in the opposite direction. The result is a pulse-step pattern of target motion with the time interval W msec defining the pulse duration. The directions of the pulse and step are always opposite but otherwise are unpredictable. Trials consisting of pulses followed by steps are intermixed randomly with a larger number of trials consisting of 6° steps alone. The experiments demonstrate that the visual system is sometimes able to cancel an eye-movement response to a pulse, on the basis of information contained in the subsequent step, to which it responds instead. As the step is delayed by progressively longer pulses, the probability increases that a response to the pulse will occur. If a response does occur in the direction of the step, it begins about 325 msec after the beginning of the step. This latency is independent of pulse time W and is about 40 msec longer than the latency of responses to steps presented alone. It is concluded that the visual system utilizes this 40 msec to operate upon a latent response to a pulse, and thereby to cancel its overt manifestation (eye movement) before initiating a response to the second, incompatible stimulus.

Hue-Wavelength Relation Measured by Color-Naming Method for Three Retinal Locations

A method of hue measurement, in which an absolute color-naming procedure is utilized, has been applied to spectral stimuli delivered as flashes at 0 degrees, 20 degrees, and 40 degrees eccentricity in an otherwise dark field. The method yields very reliable measures, especially at 0 degrees. Color-naming at 0 degrees differs little from that at 20 degrees, but a marked deterioration of performance occurs between 20 and 40 degrees. This is reflected by a reduction in red and especially green responses, and a lower reliability of the measurements. Additional estimates were also obtained which showed a decrease in measured saturation but increasing reliability of the saturation measurements with increasing eccentricity.

Vision: The Additivity Law Made To Work for Heterochromatic Photometry with Bipartite Fields

Additivity failures are common in heterochromatic photometry when the usual criterion of equal brightness is used. Using instead the criterion of a minimally distinct border between two precisely juxtaposed fields, we found that the additivity law holds.

Salience of chromatic basic color terms confirmed by three measures

Using single color terms of their choice, nine subjects named each of 424 colors twice under carefully-controlled conditions. Compared to any other color names, the chromatic basic color terms (red, green, yellow, blue, orange, purple, brown and pink) are all used more consistently within subjects, with greater consensus between subjects, and with shorter mean response times; there is no overlap between the two categories of color names by any of these criteria. The results are interpreted as supporting the conception that basic color terms refer to fundamental sensations for which there is a specific physiological basis.

Categorical color perception of Japanese observers: Comparison with that of Americans

Ten native Japanese observers named 424 colors of the OSA Uniform Color Scales set using monolexemic color terms of their choice. The results are compared with those from seven American subjects previously studied by Boynton and Olson. It is concluded, in full agreement with the original thesis of Berlin and Kay, that there are eleven basic color terms in each language, each of which describes a fundamental color sensation dependent upon an underlying physiology that does not differ between the two groups.

Chromatic border perception: the role of red- and green-sensitive cones.

Abstract Where the perception of borders is concerned, the normal visual system is found to be tritanopic. The strength of a border depends on the relative activity of only R and G cones, no matter what the B cones are doing. Since normal color vision depends on the activity of all three cone types, chromatic border strength alone cannot be used as an index of color differences. Borders produced by spatial luminance steps or chromatic steps appear similar, except that Mach-type lateral inhibitory mechanisms, which enhance the visibility of low-contrast luminance borders, are unnecessary to predict chromatic border strength. Two functions are presented, using only the responses of R and G cones, which provide a way of expressing chromatic border strength in terms of either a subjective rating scale or a luminance step that appears to be equivalent in its distinctness.

The Gap Effect: Chromatic and Achromatic Visual Discrimination as Affected by Field Separation

The effect upon visual discrimination of slightly separating the fields to be compared was tested for three conditions. Luminance discrimination was impaired, but chromatic discriminations were either unaffected or improved, depending upon the colours used. The results are explained in terms of three factors (distance, contour enhancement, averaging), two of which can be expected to behave differentially, depending upon the nature of the discrimination.