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At least 1,243 records · Page 69Linked to original sources
PubMed1993

Theory of wavelength discrimination in tritanopia.

Many theories of color discrimination predict a discontinuity in the wavelength-discrimination function of a tritanope at the point in the spectrum at which the rate of change of the visual signal constrained to an equiluminant plane passes through zero (near 460 nm). The predicted discontinuity follows from the use of a first-order approximation for which the reciprocal of the slope of the response function that generates the visual signal is proportional to the discrimination limen. In view of the good discrimination shown by such observers elsewhere in the spectrum, however, such a singularity is impossible. I show that the inclusion of the higher-order terms produces a finite value in the 460-nm region that falls in the range of values from the literature that have been obtained experimentally.

Color Perception↗
PubMed2003

Attentional capture by colour and motion in cerebral achromatopsia.

Cerebral achromatopsia is a rare condition in which damage to the ventromedial occipital area of the cortex results in the loss of colour experience. Nevertheless, cortically colour-blind patients can still use wavelength variation to perceive form and motion. In a series of six experiments we examined whether colour could also direct exogenous attention in an achromatopsic observer. We employed the colour singleton paradigm, the phi motion effect, and the correspondence process to assess attentional modulation. Although colour singletons failed to capture attention, a motion signal, based solely on chromatic information, was able to direct attention in the patient. We then show that the effect is abolished when the chromatic contours of stimuli are masked with simultaneous luminance contrast. We argue that the motion effect is dependent on chromatic contrast mediated via intact colour-opponent mechanisms. The results are taken as further evidence for the processing of wavelength variation in achromatopsia despite the absence of colour experience.

Analysis of Variance↗
PubMed1992

Dichromats detect colour-camouflaged objects that are not detected by trichromats.

To explain the surprisingly high frequency of congenital red-green colour blindness, the suggestion has been made that dichromats might be at an advantage in breaking certain kinds of colour camouflage. We have compared the performance of dichromats and normal observers in a task in which texture is camouflaged by colour. The texture elements in a target area differed in either orientation or size from the background elements. In one condition, the texture elements were all of the same colour; in the camouflage condition they were randomly coloured red or green. For trichromats, it proved to be more difficult to detect the target region in the camouflage condition, even though colour was completely irrelevant to the task. Dichromats (n = 7) did not show this effect, and indeed performed better than trichromats in the camouflage condition. We conclude that colour can interfere with segregation based upon texture, and that dichromats are less susceptible to such interference.

Color Perception↗
PubMed1993

Pop-out of orientation but no pop-out of motion at isoluminance.

Line textures in which one line was orthogonally oriented to the rest were briefly presented at various colour and luminance contrasts to the background. Subjects were able to detect the single line element pre-attentively even when the texture pattern was defined only by colour, indicating that "pop-out" of orientation is achieved at isoluminance. To exclude the possibility that this result was caused by luminance artefacts, especially by chromatic aberration, we carried out two control experiments. First, we showed that subjects could not detect a single moving line in a stationary texture under comparable conditions. Secondly, we repeated the experiments with a deuteranope who was unable to detect the differently oriented target under conditions under which the normal subject still could see it.

Adult↗
PubMed1995

Saccades to large coloured targets stepping in open fields.

Subjects tracked a 2.3 deg target that stepped 5 deg, in a randomly chosen direction, each time it was foveated. Targets were coloured patches that were fairly close to white; in some cases precise matches ensured equiluminosity with the background. Viewing conditions provided good colour rendering and neutral colour adaptation. Pale colours were surprisingly well tracked. Multiple regressions showed that the colour and spatial characteristics of the target are important determinants of a primary saccade's latency. Significant factors included target size, achromatic contrast, tritanopic purity difference, and chromatic saturation. Colour-normal subjects always responded more slowly to yellow or blue targets which a deuteranomalous subject tracked quite well. Severely blurring the target had a consistent minor effect.

Adult↗
PubMed2004

Visual search and the conspicuity of coloured targets for colour vision normal and colour vision deficient observers.

BACKGROUND: Colour is known to facilitate visual search although its role as a determinant of target conspicuity is not so clear. People with abnormal colour vision have problems recognising and differentiating colours but the extent to which they may be at a disadvantage in visual search when redundant colour is a target attribute has not been investigated previously. METHOD: Six colour normal and 29 colour deficient subjects (7 P, 6 D, 7 PA, 9 DA) were instructed to find a diamond-shaped target embedded in a background of 138 differently shaped distracters and to report its position as quickly as possible. The target was redundantly colour-coded red, yellow, green, blue or white and the distracters had the same colours in various combinations. The target was uniquely colour-coded in some presentations, partially redundant in others and in some presentations the target and distracters had the same colour. In experiment 1 the displays were presented for 20 seconds and search time was measured; in experiment 2 the exposure time was 500 ms and the proportion of targets located correctly was taken as a measure of the target's conspicuity. RESULTS: Unique colour coding reduced search times significantly and greatly enhanced conspicuity but had no benefit when some distracters had the same colour as the target. Observers with colour vision deficiency had longer search times and the coloured targets were less conspicuous to them compared with colour normal observers. However, unique colour coding assisted their search, especially when the targets were red, blue or white. CONCLUSIONS: Observers with colour vision deficiency are less efficient than colour normal observers at visual search when the target is marked out by colour and coloured targets are less conspicuous for them.

Adult↗
PubMed1984

A rod monochromat's pattern VECP at high and low background levels: spatial tuning of colour mechanisms and rods compared.

The visually evoked cortical potential spatial-tuning function, i.e. checksize vs amplitude of response, was determined for a rod monochromat at a low background level of 0.2 scot td or a high background level of 200 scot td. The results showed evidence of a peak at 36' for the low-background spatial-tuning curve, but almost no peak was evident when the high background level was employed. This latter finding was interpreted as consistent with a rod saturation effect. Additionally, the shape of the spatial-tuning function found with the low background level was compared with that obtained from the blue or red (R) and green (G) cone mechanisms of normals. It was concluded that the blue cone mechanism may not use, as has been hypothesized, the same neural transmission pathway as rods because its spatial-tuning curve differed from both the rod and R and G systems.

Adult↗
PubMed1975

Recognition of traffic signals viewed through colored filters.

Experiments were carried out to provide an empirical basis for setting color standards for sunglasses. Nineteen individuals, ten with anomalous color vision, viewed traffic signals through a series of color filters. Limits on the apparent color shift for the amber and green signals as well as for D65 are presented on a 1931 CIE chromaticity diagram. Limits on the reduction in the apparent luminosity for each of the three signals are given in terms of the minimum transmittance of the lens for each signal.

Automobile Driving↗
PubMed1983

Two additional benefits of dark glasses on rod vision in patients with congenital achromatopsia.

The visual performance of nine rod monochromats was measured with photopic stimuli viewed through filters that attenuated the ambient illuminance. In kinetic perimetry experiments, eight of nine patients showed substantially larger visual field size under the experimental as compared to the control conditions. In increment threshold or brightness-matching experiments, long wavelength sensitivity was shown to be enhanced under the experimental conditions.

Adolescent↗
PubMed1980

Central achromatopsia: behavioral, anatomic, and physiologic aspects.

The neuropsychologic, neuroanatomic, and neurophysiologic correlates of achromatopsia were studied in two patients. Prosopagnosia accompanied the color perception defect in the bilateral case but not in the unilateral one. No other neuropsychologic disturbance was present in either case. The lesions compromised the ventromedial sector of the occipital lobe in both cases. Cerebral evoked responses produced by pattern shift stimulation were normal for black and white but abnormal for red and green, when stimulation was given in the achromatopsic field.

Cerebral Infarction↗
PubMed2006

Advantage of dichromats over trichromats in discrimination of color-camouflaged stimuli in humans.

This study investigated whether 12 participants with color-vision deficiency had superior visual discrimination of color-camouflaged stimuli shown on a computer screen compared with 12 participants with normal trichromatic vision. Participants were asked to distinguish a circular pattern from other patterns in which textural elements differed from the background in orientation and thickness. In one condition, stimuli were single-colored, green or red; in the other condition, stimuli were color camouflaged with a green and red mosaic overlaid onto the pattern. Color-vision deficient participants selected the correct stimuli in the color-camouflaged condition as quickly as they did in the single-colored condition. However, normal color-vision participants took longer to select the correct choice in the color-camouflaged condition than in the single-colored condition. These results suggest that participants with color-vision deficiency may have a superior visual ability to discriminate the color-camouflaged stimuli.

Adult↗
PubMed1978

Association and dissociation of visual functions in a case of bilateral occipital lobe infarction.

A severe restriction of the visual field was observed in a patient suffering a bilateral occipital lobe infarction. Soon after the lesion, the visual field had an angle of approx. 4 degrees. Some recovery was observed within the following months. Within the restricted visual field, several visual functions were tested. Increment threshold, for instance, was found to be one log unit higher than would normally be expected. Color vision was completely lost soon after the lesion, but some recovery was later observed. Although binocular interaction was demonstrated by the interocular transfer of after-effects, the patient never experienced steropsis. He also seemed unable to recognize faces. Dsepite the small visual field, optokinetic nystagmus could be elicited. A notable slowing down of visual analyses was observed in experiments on visual reaction time, on the inversion of the Necker cube, and on binocular rivalry. The complete loss of certain functions like steropsis or face recognition in contrast to a quantitative reduction of other functions like visual acuity or color perception can be discussed in the light of two conceptual models of perceptual processing. One model suggests the representation of different visual functions within one neuronal network, each function represented by a different number of neurons or a different algorithm within the network. The second model suggests a spatial segregation of different visual functions in different cortical areas that receive input from one common structure, presumably the striate cortex.

Aged↗