Additive effect of backgrounds in chromatic induction.
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Adaptation, Ocular↗
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Chromatic organization of a cichlid fish retina.
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Animals↗
Latencies for chromatic and achromatic visual mechanisms.
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Afterimage↗
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.
Adaptation, Ocular↗
Interocular transfer of a chromatic frequency shift.
Interocular transfer of a spatial frequency shift was obtained with equiluminous color gratings. Gratings which combined both color and luminance contrast yielded small aftereffects and no interocular transfer. Recent electrophysiological work has uncovered color-sensitive binocularly driven cells in visual cortex. These cells are transient and often respond to color contrast in the absence of luminance contrast. The stimulus parameters associated with successful interocular transfer, equiluminous colors and brief test, matched the properties of these cells. Previous failure to induce interocular transfer of color effects may be explained by inappropriate stimulus parameters.
Adaptation, Ocular↗
Transient processing in chromatic induction.
The non-additivity of steady backgrounds and superimposed test flashes was investigated with 25 observers using a hue cancellation procedure. The subject's task was to vary the ratio of two lights comprising an incremental test flash (delta R/delta G) so as to maintain a unique yellow hue (i.e. red-green equilibrium) in the presence of a long-wavelength adapting background. Measurements were obtained for four different luminances of the test flash (for each background), covering a range of 1.5-2.0 log units. The adaptive hue shifts generally support Walraven's finding that the background affects the hue of the test flash only by way of altering the spectral sensitivities of the receptors, but it does not add to the hue signals from the test flash.
Adaptation, Ocular↗
Color perception under chromatic adaptation: "supersensitivity" with dim backgrounds.
The amounts of 540 nm light and 660 nm light that when mixed result in a yellow (neither reddish nor greenish) percept remain in constant ratio, regardless of the total retinal illumance level of the mixture. A similar result holds if the mixture is superimposed upon a very dim 660 nm adapting field, except that a larger proportion of 540 nm light is required than in the dark (contrary to an effect of receptor desensitization, which would result in a smaller proportion of 540 nm light). Mixtures of 460 and 579 nm lights that give yellow/blue equilibrium percepts show the same effect: under very dim 579 nm adaptation, a larger proportion of 460 nm light is required than in the dark. These results cannot be accounted for by cone sensitivity reduction nor by a postreceptoral restoring effect; they reveal an additional mechanism of adaptation.
Adaptation, Ocular↗
Depolarizing responses of L-type external horizontal cells in the goldfish retina under intense chromatic background.
The external horizontal cells (EHCs) in the goldfish retina are known to respond with hyperpolarization to monochromatic flashes of all wavelengths. From their spectral responses they are referred to as "monophasic" horizontal cells. However, when the retina is exposed to an intense red background, EHCs showed a depolarizing response to flashes of intermediate and short wavelength of moderate intensity. The depolarizing component is presumably driven by the input from green-sensitive cones.
Animals↗
Chromatic properties of the retinal afferents in the thalamus and the tectum of the frog (Rana temporaria).
In order to clarify physiological mechanisms underlying colour-specific visually guided behaviour, we measured spectral sensitivities of On-fibres projecting to the thalamus and class 2 and 3 fibres passing to tectum opticum. In addition we recorded responses of these fibres to moving coloured papers with known spectral reflectancies. The latter method, here called paper colourimetry, allowed us to change the relative stimulations of the blue-, green- and red-sensitive photoreceptors in any direction desired. Under the photopic conditions used the tectal fibres were driven exclusively by red-sensitive receptors, while the thalamic fibres received strong On-inputs from both red- and blue-sensitive receptors. Due to a partly antagonistic interaction between these inputs the On-fibres acted in a dichromatic way, responding with specific extended low-frequency discharges to all relative increases in blue receptor stimulation, e.g. to a great reduction in red stimulation combined with unchanged blue stimulation. Thus they have functional characteristics which could serve a visual system showing colour constancy.
Action Potentials↗
Temporal modulation sensitivity of the blue mechanism: measurements made with extraretinal chromatic adaptation.
Using the counterphase-modulated-tritan-metamers method of Wisowaty and Boynton [Vision Res. 20, 895-909 (1980)], we measured the modulation sensitivity function of the blue mechanism on dark backgrounds and on uniform yellow backgrounds that were produced either by illuminating the retina with yellow light or by filling-in of a stabilized retinal image. When measured on yellow backgrounds, temporal modulation sensitivity was markedly reduced whether the background was produced by retinal illumination or by filling-in. This sensitivity reduction has been attributed by other researchers to changes in the transmission characteristics of the blue/yellow pathway caused by yellow adaptation. Our results obtained with backgrounds that appeared yellow due to filling-in indicate that the site of adaptation must be extraretinal as there was no yellow light reaching the retina in the vicinity of the test probe.
Adaptation, Ocular↗
Effects of field area and configuration on chromatic and border discriminations.
Visual discrimination was tested with juxtaposed fields that differed only in luminance, S cone excitation, or the ratio of L to M cone excitation. Observers were asked to make discriminations based upon a criterion of color difference or of the perception of a border between fields. The area of the fields was varied either by increasing the length of their common junction or by increasing their widths at constant junction length. For fields larger than 0.2-0.4 deg2, area controls sensitivity. For smaller fields, discrimination may be worse for narrow fields with long common junctions than for wide ones with small common junctions, especially for discriminations that depend upon S cones, in which the field components tend to become spatially integrated. Decreasing viewing time reduces the magnitude of this effect. S cone and L-M channel acuities were estimated at about 7 and 32 c/deg, respectively.
Adult↗
Phase discrimination in chromatic compound gratings.
Phase discrimination thresholds were measured for yellow/green isoluminant and non-isoluminant compound gratings in which the amplitude of the two components (f and 3f) was twice the detection threshold. The phase discrimination threshold at isoluminance was worse than in all the other conditions, which gave broadly similar threshold data. It is suggested that this is due to a positional uncertainty in the neural representation of the isoluminant stimuli.
Contrast Sensitivity↗
On the loss of apparent motion between isolated chromatic stimuli near isoluminance.
Long range apparent motion (AM) between two isolated stimuli breaks down following prolonged inspection. Time-till-breakdown (TTB) for AM between random-dot squares (red or green) on a red random-dot background was measured as a function of luminance contrast of the stimuli against the background. For the same-color (red squares on the red background) and the different-color (green squares on the red background) conditions, TTB showed clear dependence on the luminance contrast, diminishing with decreasing the contrast. Near isoluminance (luminance contrast of approx. -14 to +14%), AM for the same-color condition disappeared, but AM for the different-color condition was clearly seen and persisted for 7-14 sec. These results show that AM can be produced by color alone. Previous controversial question on the loss of long range AM near isoluminance may be explained by taking into account the contrast dependence of the breakdown effect and the experimental procedures employed.
Color Perception↗
Spatial and chromatic interactions in the human pattern electroretinogram.
The spectral sensitivity and the spatial selectivity was studied both psychophysically and electroretinographically using the pattern onset-offset paradigm. All measurements were made under intensive yellow adaptation. The spectral sensitivity functions of both measures were in close agreement. They showed a peak at 460 nm (blue-sensitive mechanism) and a shoulder around 550 nm (red-green-sensitive mechanism). The luminance curves of the pattern onset ERG obtained with long wavelengths had a steeper slope and reached larger amplitudes than those obtained with short wavelengths. In addition the response-peak times were longer with short wavelengths. When the spatial frequency of the pattern was varied the 460 nm-onset responses showed very little or no spatial tuning and long peak times (around 60 msec). This was ascribed to the contribution from only one type of ganglion cell, namely the blue-yellow opponent receptive fields lacking a center-surround organization. The 550 nm-onset responses showed a clear spatial tuning (4 c/deg) and an increase in peak time (40-50 msec) with increasing spatial frequency (0.26-9.2 c/deg). This was ascribed to different types of receptive fields having a center-surround structure.
Adaptation, Ocular↗
Temporal and chromatic properties of motion mechanisms.
We measured threshold contours in color space for detecting drifting sinusoidal gratings over a range of temporal frequencies, and for identifying their direction of motion. Observers were able to correctly identify the direction of motion in all directions of color space, given a sufficiently high contrast. At low temporal frequencies we found differences between luminance and isoluminance conditions; for isoluminance there was a marked threshold elevation for identification when compared to detection. The threshold elevation for identification is dependent on eccentricity as well as on temporal frequency. At high temporal frequencies there were no differences between detection and identification thresholds, or between thresholds for luminance and isoluminance. A quantitative analysis of the threshold contours allowed us to identify two mechanisms contributing to motion: a color-opponent mechanism with a high sensitivity at low temporal frequencies and a luminance mechanism whose relative sensitivity increases with temporal frequency. An analysis of the cone contributions to motion detection and identification showed that L-cones dominated threshold behavior for both detection and identification at high temporal frequencies. There was a weak S-cone input to motion detection and identification at high temporal frequencies.
Color Perception↗
Color perception within a chromatic context: the effect of short-wavelength light on color appearance.
Light at the boundary of a uniform test field (contrast) has a qualitatively different effect on color perception than light in more remote noncontiguous regions (context). Basic properties of color perception with contextual short-wavelength light are assessed here with a 1 degree test field surrounded by either contiguous or noncontiguous 440 or 491 nm light (32 td). Contrasting stimuli are 3 or 5 degrees adapting fields, a thin 1 degree i.d.-2 degrees o.d. (0.5 degree wide) contiguous band, or a large 1 degree i.d.-5 degrees o.d. contiguous surround. Contextual stimuli are a remote 3 degrees i.d.-5 degrees o.d. ring or 0.5 degree wide noncontiguous bands at various distances from the edge of the 1 degree test field (2 degrees i.d.-3 degrees o.d., 3 degrees i.d.-4 degrees o.d., or 4 degrees i.d.-5 degrees o.d. bands). Contiguous surrounds have little influence on color appearance, but remote noncontiguous short-wavelength light strong affects the color of the test field, shifting it toward redness. The shift toward redness increases as a thin 440 nm band is moved farther from the test field (up to 5 degrees), unlike the effect of distance on remote middle- and long-wavelength bands. Measurements comparing the effects of 440 nm and luminance-equated 491 nm light indicate a contribution from S cones.
Color↗
Ultraviolet sensitivity of three cone types in the aphakic observer determined by chromatic adaptation.
Sensitivities at 5.5 deg off-fovea from the aphakic observer superimposed on orange, purple and blue fields were obtained to estimate short-, middle- and long-wavelength cone spectra respectively. The middle-wavelength mechanism had a visible wavelength maximum resembling a nomogram plus an UV sensitivity fitting a cis-peak. The short (and, to a lesser extent, the long) wavelength cone sensitivities are higher in the UV than expected.
Adaptation, Ocular↗
Chromatic and luminance systems deficits in glaucoma.
The purpose of this study was to compare the effects of glaucoma, at different stages of the disease process, on the two color-opponent system and on the luminance system. Discrimination thresholds were measured along the two equiluminant cardinal color axes (RG and YV) and along an achromatic luminance axis (LD) in 27 patients with open-angle glaucoma (OAG) and in 13 glaucoma suspects. Patients with OAG showed increased thresholds along all three axes. The threshold increases correlated significantly with the level of visual field loss. For glaucoma suspects, thresholds were also increased along all three axes. A subgroup of patients with OAG, those with pigmentary glaucoma, showed minimal increases in threshold along the RG axis. To further investigate this finding an additional 15 patients, seven with primary OAG and eight with pigmentary glaucoma were run in a two-alternative forced-choice experiment. For patients with pigmentary glaucoma, thresholds were increased less along the RG axis. The results of the study for OAG patients and glaucoma suspects are consistent with deficits in the two color-opponent systems, and in the luminance system.
Adult↗