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PubMed1985

Synaptic contacts between red-sensitive cones and triphasic chromaticity horizontal cells in the turtle retina.

Using combined physiological and anatomical methods, we have shown that triphasic chromaticity horizontal cells (THC) in the turtle retina make ribbon synaptic contacts with about 20 cones, two-thirds were red-sensitive, while the rest were blue-sensitive. The response of THC to red flashes appeared to be generated via synapses from red-sensitive cones; this interpretation differs from those of the previous studies where only blue-sensitive cones were thought to make synaptic contacts with the THC.

Animals↗
PubMed1992

Classification of chromatic visual evoked potentials with the aid of a neural net.

Twelve normal subjects, and six color blind (three protanopes and three deuteranopes) individuals were used in this study. Visual evoked potentials (50-150 msec post-stimulus) were recorded in response to three stimuli: (a) three horizontal, achromatic bars alternating in luminosity between bright and dim, (b) bars alternating between blue and red, and (c) bars alternating between green and red. The resulting waveforms were normalized in amplitude and submitted to a commercial neural net program for classification. The network correctly identified 24 of the 36 normal responses. (2) The network was also asked to distinguish between the responses of normal and color blind individuals. Based upon the blue/red response, the network correctly classed 12 of 18 responses, and based upon the green/red response correctly classified 14 of 18 (including all 6 color blinds). (3) These results are statistically highly significant and suggest that the VEP elicited by chromatic stimulation is substantially different from that elicited by achromatic stimuli.

Classification↗
PubMed1982

Discrimination and detection thresholds: the effect of observer criterion on the spatial properties of chromatic and achromatic mechanisms.

Spectral sensitivity functions were determined for structured test targets presented on a white background field. Data obtained for threshold detection of the targets are consistent with results obtained from previous studies which used unstructured test fields showing functions, with three maxima, dependent on opponent colour mechanisms. Data obtained from threshold discrimination measurements show a marked reduction in the blue sensitivity when 1 degree test targets are used. This effect decreases significantly when larger targets are used. A change of the observer's criterion can significantly alter the relative contributions of the achromatic and chromatic channels at threshold.

Color Perception↗
PubMed1982

Color perception under chromatic adaptation: equilibrium yellow and long-wavelength adaptation.

Observers viewed a thin (0.8-1.3) annulus composed of a mixture of 540 and 660 nm monochromatic lights (denoted delta G and delta R, respectively). The annular mixture was superimposed upon a larger (2.7) 660 nm circular background field. The observer adjusted the radiance of either delta G or delta R so that the annulus appeared a perfect (i.e. neither reddish nor greenish) yellow. In the first experiment, the background and annulus both were presented steadily. The results showed that the background, varied over a range from 10 to 1000 td. always contributed less to the color appearance of the annular test area than would be expected from the simple admixture of lights. The second experiment examined the effect of briefly removing the background-field quanta during the period when the annulus was judged. After several minutes of adapting to the background, the background was momentarily extinguished for 1 sec once every 6 sec; the observer adjusted the radiance of delta R so that during the 1 sec period the continuously presented annular mixture appeared equilibrium yellow. With steady backgrounds, the delta G to delta R luminance ratio decreased with test annulus luminance; for judgments made while the background momentarily was extinguished, the luminance ratio generally increased with annulus luminance. All of the empirical observations can be accounted for quantitatively by a two-process theory of chromatic adaptation; in two processes are (1) gain changes and (2) a restoring signal that tends to drive back toward equilibrium the opponent response resulting from the adapting light. Results from a third experiment, in which the background-off interval was reduced from 1 sec to 500, 200 or 150 msec. also are consistent with this model.

Adaptation, Ocular↗
PubMed1984

Interocular transfer of a chromatic frequency shift: temporal constraints.

Interocular transfer of a chromatic version of the Blakemore and Sutton (1969) [Science 166, 245-247] spatial frequency shift is not obtained with long steady (3000 msec) test presentation, but does occur when the test is brief (400 msec) or flickering. By contrast, interocular transfer of achromatic spatial frequency adaptation occurs with long steady tests as well as with brief or flickering tests.

Adaptation, Ocular↗
PubMed1984

The Abney effect: chromaticity coordinates of unique and other constant hues.

We compared unique and other constant hue loci measured at a fixed retinal illuminance for the same observers. When expressed in Judd chromaticity coordinates, unique hue and constant hue data agreed. Unique blue loci were curved, and unique red and green loci were noncollinear. These data imply that unique hues are not a linear transformation of color matching functions. Linear models are only an approximation, even at a single luminance level.

Color Perception↗
PubMed1984

Color perception under contralateral and binocularly fused chromatic adaption.

Observers viewed a thin (1.0-1.5 degree) annular mixture of 450 plus 660 nm light with the left eye, and a 4.8 degrees circular 660 nm adapting field with the right eye. The annular test was centered upon the adapting field in the fused percept. The contralateral field, which bleached negligible photopigment, caused the test to appear more reddish; however quantitative results reject the hypothesis that a given contralateral 660 nm light simply adds redness to the test. Additional experiments with a separate 660 nm adapting light presented to each eye reveal that fused chromatic adapting fields affect a complex central mechanism. For example, a dim background presented to the same eye as the annular test can reduce the effect of an opposite-eye field, even when the dim test-eye background has no measurable influence in a purely monocular experiment.

Adaptation, Ocular↗
PubMed1985

The low level motion system has both chromatic and luminance inputs.

Adaptation to moving isoluminant gratings induces a motion after-effect (MAE). Isoluminant gratings are less effective at inducing and at nulling MAEs than are luminance gratings. These results are consistent with a low-level motion detection system which operates on signals from mechanisms which show both spatial and chromatic opponency.

Adaptation, Ocular↗
PubMed1985

Additivity of red chromatic valence.

The additivity of red chromatic valence was investigated by the hue cancellation method for 4 normal observers. Additivity held for wavelength combinations of 610-680 nm and 400-440 nm. When using 400-680 nm, additivity failure of enhancement type was found for two observers, reduction type failure for a third, and additivity, for a forth. The results suggest a nonlinear property of the red-green process for some observers and are discussed in terms of the contribution of B-cones to the process.

Adaptation, Ocular↗
PubMed1985

Reaction times to chromatic stimuli.

The relative contributions of chromatic and achromatic activity to reaction time were investigated under conditions in which spatial and temporal transients were manipulated. Simple reaction times (RT) were obtained to eight photometrically matched (1 cd/m2) wavelengths between 448 and 658 nm. These stimuli were incrementally presented on a spatially coextensive 1.2 degrees white adapting field. RT was wavelength dependent for 5 or 10 cd/m2 steady backgrounds or a 5 Hz 1.2 cd/m2 flickering background. RT varied as a trichromatic saturation-like function (slowest RT at 572 nm). In comparison, RT was wavelength independent when no adapting field was present and when the 1.2 cd/m2 field was flickered at 15 Hz.

Adaptation, Ocular↗
PubMed1985

Stereopsis with chromatic signals from the blue-sensitive mechanism.

Evidence is presented that the depth seen in dim violet targets superimposed on a bright yellow background is mediated solely by the blue-sensitive mechanism. In forced-choice experiments using these stimuli, observers could discriminate between crossed and uncrossed disparities when the targets were either figural or random dot stereograms. Stereo thresholds for a three bar target whose spatial parameters were adjusted for the B cone mechanism were on the order of 40 sec of arc, a value considerably smaller than the spacing between B cones. With the additional assumption that signals from the blue-sensitive mechanism do not contribute to luminance, these results confirm that purely chromatic signals have access to stereoscopic mechanisms.

Color Perception↗
PubMed1985

Chromatic and spatial information processing by red cones and L-type horizontal cells in the turtle retina.

Flash sensitivities to red (694 nm) and green (546 nm) light were measured intracellularly from red cones and L-type horizontal cells in the turtle retina. The horizontal cells' sensitivity to short wavelength light was significantly larger than expected from the model where horizontal cells receive input mainly from red cones. The red cone responses to chromatic stimuli were strongly dependent upon the flash colour and size. Increasing the spot size reduced the sensitivity to green relative to red and augmented the differences in kinetics between the response to red light and that evoked by green light. It was concluded that L-type horizontal cells received a short wavelength input in addition to the input from red cones. This additional green input coupled with the negative feedback pathway from horizontal cells onto red cones determined the differential spatial properties of the red cone responses to red and green test flashes.

Animals↗
PubMed1985

Positional acuity with chromatic stimuli.

Theoretical reasons are presented for expecting a high precision spatial acuity task (vernier acuity) to be more difficult with an equiluminous stimulus than with stimuli containing luminance cues. This prediction was verified in Experiment 1. In a second experiment, it was shown that the result of the first experiment could not be explained by reduced detectability of the equiluminous target bar. We explain these results by the conflicting demands of chromatic and spatial differencing within a single mechanism, and propose that this also explains the similarities between long and medium wavelength cones in their spectral sensitivities.

Color Perception↗
PubMed1986

The longitudinal chromatic aberration of the human eye, and its correction.

The human eye suffers from longitudinal chromatic aberration, and this has been thought to average approximately 1.75 D between 420 and 660 nm. In many vision experiments the aberration may be a serious problem, and a number of lenses have been designed to correct it, two of which have recently been commercially available. These achromatising lenses produce an equal but opposite aberration to that of the average eye, and the power of the eye/lens combination should then be independent of wavelength. Recent measures of the eye's longitudinal aberration suggest that the average may be substantially greater than the above value, in which case lenses based on this figure should be inadequate. Using a Badal optometer we determined the far points for 20 subjects with each of the recent lenses, and without either, at nine wavelengths over the above range. Consistent with the early studies we found an average aberration of 1.82 D (SD 0.15 D). Both lenses performed as specified, and none of our subjects had over 0.48 D of residual aberration when corrected with either.

Adult↗
PubMed1986

Additivity of yellow chromatic valence.

The additivity of yellow chromatic valence was investigated by the hue cancellation method for two normal observers. Additivity held in 530-550 nm and 600-630 nm pairs, while additivity failure of reduction type occurred in 530-570 nm pair for both observers. Additivity failure of enhancement type occurred in 530-600 and 530-630 nm pairs in which one observer showed reduction type failure when mixture ratio of 530 nm is greater than 600 or 630 nm. The results suggest a nonlinear property of the yellow-blue process and are discussed in an interaction between the two opponent processes.

Color Perception↗
PubMed1986

Spatial and chromatic antagonism between the long- and middle-wavelength cones in the detection of long-wavelength flashes.

Field additivity was tested for small red increments on small and large adapting fields. The results for a large adapting field showed the failure of field additivity of the cancellation type, providing strong evidence for cone-antagonistic coding, while the results for a small adapting field showed field additivity. The cancellation effect took place concurrently with the spatial sensitization effect, thus suggesting that the spatial and chromatic antagonism occur concomitantly at some stage in the detection pathway.

Color Perception↗
PubMed1987

Simulation of responses of spectrally-opponent neurones in the macaque lateral geniculate nucleus to chromatic and achromatic light stimuli.

The responses of spectrally opponent, parvocellular-layer cells in the lateral geniculate nucleus of the macaque vary with stimulation along all three dimensions of colour space (luminance, dominant wavelength and purity). Here, the responses of different cell types to light stimuli successively replacing a white adaptation field are simulated mathematically by a simple model using known cone spectral sensitivities. Hyperbolic response functions with two adjustable parameters relate cone excitation with the output signals of each cone mechanism. For the majority of cells, differences of outputs of two cone mechanisms, receiving inputs from L- and M-cones, describe responses to chromatic and achromatic stimuli. For each opponent combination of cone inputs, either L-M or M-L, two cell types were found. Off-centre cells had lower maximum firing rates of their on-component, but were the more sensitive of the two groups, preferring dark colours, whereas on-centre cells showed better responsiveness to brighter stimuli. For all four cell types, the predictions of the equations replicated well the responses measured to stimuli varying along all three dimensions of colour space. The quantification of cell responses presented here provides possibilities for studying suprathreshold coding of colour and lightness, and the model can help to link physiology with the psychophysics of colour vision.

Animals↗
PubMed1988

Color perception under chromatic adaptation: red/green equilibria with adapted short-wavelength-sensitive cones.

Chromatic adaptation can dramatically alter the color appearance of a light. The specific effect of adapting short-wavelength-sensitive (SWS) cones is examined by using two adapting wavelengths that lie on a tritanopic confusion line. The change in color appearance caused by signals from adapted SWS cones is isolated by restricting the wavelengths of the test light to 550 nm or longer. Thus the test negligibly stimulates SWS cones, so their sensitivity does not affect the test's appearance. The results show that adapted SWS cones contribute redness to the appearance of a superimposed test light, while not affecting sensitivity of MWS and LWS cones. Quantitatively, the redness from SWS cones illuminated by a large adapting field approaches physical admixture of test and adapting lights. This is very different from an adapting field that stimulates only MWS and LWS cones which, due to a postreceptoral process, contributes much less redness to a small superimposed test than expected from admixture. The difference between the adapted SWS-cone and the adapted MWS/LWS-cone contributions to the color of a small test explains a surprising result: a bluish-green (491 nm) adapting field contributes redness to a superimposed test light.

Adaptation, Ocular↗