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R M Boynton

Publications and source records attributed to R M Boynton.

At least 37 records · Page 2Linked to original sources
PubMed1982

Field sensitivity of the "red" mechanism derived from primate local electroretinogram.

Using the local ERG in response to a long-wavelength stimulus as an indicator, field sensitivity functions have been obtained from cynomolgus macaque monkeys (Macaca fascicularis) with flashed and sinusoidally flickering test stimuli. These functions show the reciprocal of the relative radiance, for various adapting wavelengths, required to reduce a 667-nm test response to a criterion level. The resulting functions resemble both Stiles's pi 5 and the SR function of Smith and Pokorny, provided that pi 5 and SR are displaced about 7 nm toward longer wavelengths, in agreement with microspectrophotometric evidence. When field sensitivity functions are obtained with a 20 Hz sinusoidal test stimulus, using a continuous change of field wavelength, the direction of a slow spectral traverse has a large effect upon the shape of the sensitivity and phase functions--a hysteresis effect These effects do not occur at 5 Hz. The test light is proven to be ineffective upon G cones, and it appears unlikely that measurably significant signals are significantly induced into G cones as an indirect result of the modulation of R cones. Therefore, the steady background light absorbed in the G cones seems to be influencing the response of the R cones.

Adaptation, Ocular↗
PubMed1981

Visibility of borders: separate and combined effects of color differences, luminance contrast, and luminance level.

The strength of the border between two regions was assessed by measuring the tendency of the border to disappear during a 5-min fixation period. We measured the total time the border was judged visible when subjects viewed two hemifields with different chromaticities (six wavelength pairs), five luminance contrasts, or with differences in both, at five levels of luminance. For a homochromatic field, border visibility increased linearly with the logarithm of the luminance contrast, regardless of the particular wavelength of the field. For fields with only chromatic differences, border visibility increased linearly with the logarithm of the tritanopic-purity difference (the relative activity of only the long- and middle-wavelength-sensitive cones). For all borders, visibility increased with an increase in luminance level. Thus borders formed by the combination of chromatic differences and luminance contrasts are more visible than borders that have the same chromatic difference or the same luminance contrast alone. For any chromatic difference, calculations of a luminance contrast that would yield the same border visibility were made. These equivalent luminance-contrast functions for border visibility provide a metric for chromatic differences across a range of luminances that allows chromatic and luminance-contrast sensitivities to be compared in a nonarbitrary way. Relative to chromatic differences, luminance contrast is less effective in maintaining border visibility at lower luminance levels. When the borders combine both chromatic differences and luminance contrasts, a root-mean-square model can be used to account for the data. This is consistent with the idea that chromatic and luminance systems make independent contributions to the visibility of borders.

Color↗
PubMed1980

Equations for chromatic discrimination models.

Equations are derived to fit the cone sensitivity values of Smith and Pokorny, which are based mainly upon Judd's modified color matching functions and the spectral sensitivities of normal and dichromatic observers. The equations, which fit Smith and Pokorny's values to within 1 to 3%, are smooth and differentiable. Derivatives of cone sensitivities for an equal luminance spectrum, which are of particular importance for models of chromatic discrimination, have been calculated and are shown graphically.

Color Perception↗
PubMed1979

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.

Color Perception↗
PubMed1979

Large-field color naming of dichromats with rods bleached.

A color-naming method was used to examine the large-field red/green discriminations of dichromats screened with standard tests. The stimulus was a 12 degrees annular field with the central 4 degrees removed, flashed for 300 ms. Four wavelengths were equated in brightness for each observer at two retinal illuminance levels, approximately 10 and 100 trolands. The stimuli were then presented in random order and the observer was asked to name each, using one of four color terms. The entire experiment was done with the observers dark-adapted and also with the rods bleached. For all four deuteranopes and two of four protanopes, color names were very significantly related to both illuminance and wavelength in both adaptation conditions. The relationship between name and wavelength was similar to that of a normal trichromat, but the performance of a dichromat was very poor by comparison. Performance was generally somewhat better in the dark than with the rods bleached. However, the result in the bleached condition is consistent with recent evidence that at least some observers who are classified as dichromats with standard small-field screening procedures actually have a weak residual third cone mechanism.

Adaptation, Ocular↗
PubMed1976

Primate flicker sensitivity: psychophysics and electrophysiology.

A quantitative comparison is made between the psychophysical flicker response of man and similar data obtained electrophysiologically from the cones of macaque monkeys. When the psychophysical data are obtained from an eye that is strongly light-adapted, there is excellent agreement between the two sets of data at high frequencies. Under this condition, both kinds of data fit a distributed-parameter model, whose time constant also agrees with that derived from studies of the phosphenes elicited by electrical stimulation of the human eye. On the other hand, psychophysical data obtained with fully modulated stimuli (which minimally adapt the eye) yield a longer time constant for the same model. These results imply that the psychophysical flicker thresholds are normally controlled by a distributed filtering process that is proximal to the receptor stage. This slower, psychophysical process is evidently desensitized by intense adapting lights, so that the faster one that governs the electrophysiological responses can be detected.

Animals↗
PubMed1976

A line, not a space, represents visual distinctness of borders formed by different colors.

When observers are asked to rate the visual distinctness of borders formed by the junction of two photic stimuli, normal trichromatic subjects behave in a manner similar to that of tritanopes in a color mixture experiment. All stimuli that look the same to the tritanope produce the same border distinctness with any other stimulus. Sets of such stimuli, whose members do not form borders with each other, map as single points along a curved line, where the Euclidean distance between pairs of points representing the two stimuli is nearly proportional to the rated distinctness of the border formed between them. In the absence of luminance differences, the perception of contour apparently depends on the stimulation of only two cone types.

Color Perception↗
PubMed1975

Response of primate cones to sinusoidally flickering homochromatic stimuli.

1. The response of the primate cone photoreceptors to sinusoidally flickering stimuli has been obtained by monitoring the late receptor potential (LRP). 2. By comparing the response characteristics of the foveal local electroretinogram (LERG) before and after the intraocular infusion of sodium aspartate, it was found that the b-wave in the foveal LERG does not affect the monitoring of the LRP to steady-state flicker. 3. Functions describing the supra-threshold frequency response characteristics of the photoreceptors were obtained. 4. Linearity was found to hold for low amplitude responses, and temporal modulation transfer functions (MTFs) were obtained for the photoreceptors at various adaptation levels. 5. The cone photoreceptors were found to act approximately as passive low pass filters compounded with some low frequency attenuation. 6. The high frequency response of the photoreceptors at various adaptation levels tends toward a common high frequency asymptote, much like human psychophysical findings, and can be described by a diffusion model. 7. Non-linearities (convexity-upwards) suggest modest positive feedback at the level of the photoreceptors. 8. Mechanisms limiting the magnitude of the receptor response at low frequencies have little effect on the phase lag of the response.

Adaptation, Ocular↗
PubMed1975

Sinusoidal flicker characteristcis of primate cones in response to heterochromatic stimuli.

Electrophysiological recordings of primate photorecptors have been obtained and frequency response characteristics of the red, green and blue cones have been determined and compared to previous psychophysical findings. Using cynomolgus monkeys, we recorded the foveal local electroretinogram, which is dominated by the late receptor potential, and obtained criterion-response threshold data for sinusoidally flickered test stimuli complementary chromatic adapting backgrounds. Our results support the hypotheses that (a) the shapes of the MTFs of the red and green cone systems are identical and are determined solely by the photoreceptors at high frequencies, and (b) the blue cones have an MTF with a lower corner frequency than the red- and green-cone systems.

Adaptation, Ocular↗