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Results for “Color Perception”

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PubMed1978

A possible explanation as to why the newly sighted commonly perform well on pseudoisochromatic colour vision tests.

Patients whose vision has been restored after long periods of blindness commonly experience difficulty in perceiving. Parodoxically, such patients often perform well on pseudoisochromatic colour-vision tests. A well-known example is Gregory and Wallace's subject, S.B. who performance on the Ishihara test was perfect. It is suggested that restoration of vision may be associated with relatively poor visual acuity and that this, by filtering higher spatial frequencies, enhances the legibility of pseudoisochromatic test patterns. Two experiments confirm that the Ishihara plates are more legible when seen as defocused images.

Blindness↗
PubMed1991

Colour changes as a function of luminance contrast.

When spectral light increases in luminance, the hues change. Normally, long-wavelength light becomes increasingly yellow, and short-wavelength light turns blue or blue-green. This is known as the Bezold-Brücke hue shift. Less notice has been paid to the change in relative chromatic content (saturation or chromatic strength) that accompanies these shifts in hue. As luminance contrast increases from zero, chromatic strength increases to reach a maximum at a luminance that is wavelength dependent. Short-wavelength blueish light reaches this maximum at low relative luminances, whereas midspectral yellowish stimuli need several log units higher luminance. Red and green are somewhere in between. For luminances above this maximum, the chromatic content usually diminishes, and most light becomes more whitish in appearance. In this study it is demonstrated how the combined chromatic appearance of hue and chromatic strength change with intensity. Both phenomena find a common physiological interpretation in the nonlinear and nonmonotonic responses of colour-opponent P cells in the retina and lateral geniculate nucleus of the primate. A model that combines the outputs of six P-cell types accounts for observers' estimates of hue and chromatic strength.

Attention↗
PubMed1997

A vector model of colour contrast in a cone-excitation colour space.

A vector model of colour contrast is examined in a colour space that is a logarithmic transformation of the MacLeod-Boynton cone-excitation diagram. Observers set matches in a haploscopic display, in which one eye viewed a standard display (a neutral target square in a coloured surround) and the other viewed a matching display (a variable square in its own surround). Contrast colours are simply represented in this colour space: the vector connecting the right-eye surround and matched chromaticities is parallel to and to the same length and direction as the vector that connects the left-eye (standard) surround and square chromaticities. This describes observers' matches to the hues induced in a neutral square for a range of inducing surround colours, a range of right-eye (match) surround colours and four different luminance contrasts.

Adult↗
PubMed2005

One blue colour channel or two?

Contrary to the general belief that the yellow-blue mechanism has lower spatial resolution than the red-green mechanism, it has been recently claimed that both mechanisms have similar spatial sensitivity (McKeefry et al, 2001 Vision Research 41 245-255). Studying high-spatial-frequency tritanopia (a colour illusion based on spatio-chromatic interactions in human vision), we found strong evidence for the existence of two blue mechanisms-with low and high spatial-frequency resolution. If confirmed, this may resolve the apparent paradox concerning spatial resolution of the yellow-blue mechanism.

Color Perception↗
PubMed2005

Colour matching of isoluminant samples and backgrounds: a model.

A cone-opponent-based vector model is used to derive the activity in the red-green, yellow-blue, and achromatic channels during a sequential asymmetric colour-matching experiment. Forty Munsell samples, simulated under illuminant C, were matched with their appearance under eight test illuminants. The test samples and backgrounds were photometrically isoluminant with each other. According to the model, the orthogonality of the channels is revealed when test illuminants lie along either red-green or yellow blue cardinal axes. The red green and yellow-blue outputs of the channels are described in terms of the hue of the sample. The fact that the three-channel model explains the data in a colour-matching experiment indicates that an early form of colour processing is mediated at a site where the three channels converge, probably the input layer of V1.

Case-Control Studies↗
PubMed1999

Mechanisms of color constancy under nearly natural viewing.

Color constancy is our ability to perceive constant surface colors despite changes in illumination. Although color constancy has been studied extensively, its mechanisms are still largely unknown. Three classic hypotheses are that constancy is mediated by local adaptation, by adaptation to the spatial mean of the image, or by adaptation to the most intense image region. We measure color constancy under nearly natural viewing conditions, by using a design that allows us to test these three hypotheses directly. By suitable stimulus manipulation, we are able to titrate the degree of constancy between 11% and 83%, indicating that we have achieved good laboratory control. Our results rule out all three classic hypotheses and thus suggest that there is more to constancy than can be easily explained by the action of simple visual mechanisms.

Adaptation, Biological↗
PubMed2006

A lens of many facets. Science through a family's eyes.

This essay argues for the relevance of the history of family life to the history of science, taking the example of the Exners of Vienna. The Exners were an influential case of the nineteenth-century European phenomenon of the "scientific dynasty". The focus here is on their collaborative research on color theory at the turn of the twentieth century. At first glance, this project looks like a reactionary strike against aesthetic innovation, a symptom of what historians assume was an unbridgeable gulf between scientific reason and artistic modernism. We can better understand the Exners' motivations by situating this research at the intersection of the family's public and private lives. The domestic context sheds light on their use of such scientific terms as "subjective", "normal", and "universal", providing a more nuanced sense of what rationality really meant in fin-de-siècle Vienna.

Austria↗
PubMed2002

Color contrast in macaque V1.

We explored the neural basis for spatial color contrast (red looks redder surrounded by green) and temporal color contrast (red looks redder if preceded by green) in primary visual cortex (V1) of the alert macaque. Using pairs of stimuli, we found a subset of neurons that gave stronger responses to sequences of red and green spots and stronger responses to adjacent red and green spots. These cells combined their cone inputs linearly: for a red-ON-center cell, the sum of the OFF response to green and the ON response to red predicted the peak response to red preceded by green. These 'color' cells, which could underlie hue discrimination because they show cone opponency, could mediate spatial and temporal color contrast. In contrast, the majority of cortical cells, which do not show overt cone opponency but which are often orientation tuned and/or direction selective, are by themselves incapable of mediating hue discrimination. The remarkable degree of specialization shown by cells in V1, especially that of the double-opponent color cells, is discussed.

Animals↗
PubMed1982

Age and temporal resolution in color vision: When do red and green make yellow?

The ability to temporally resolve color stimuli was compared in young and old adults. Stimuli consisted of pairs of brief green and red flashes separated by six levels of interstimulus interval and presented at two different luminance levels. Integration of the color pairs to produce reports of yellow decreased significantly with increasing interstimulus interval, particularly for the younger group. This difference remained when the age-related loss in retinal illumination was compensated by increased stimulus luminance. These data indicate a decline with age in temporal resolution in color vision. Further, they suggest that age differences in temporal resolution can be more appropriately attributed to age-related differences in visual/neural mechanisms than to changes in the ocular media or photoreceptor activity.

Adult↗
PubMed1975

Racial differences in color vision: do they exist?

The present experiment investigated the possibility that variation in fundus pigmentation among individuals may be related to differential color sensitivity. Fifty black and white observers representing a wide range of skin (and fundus) pigmentation made direct heterochromatic brightness matches for a white standard field against each of five chromatic comparison fields. Results indicated that pigment (i.e., racial) differences in color vision do not exist, as measured by the two psychophysical methods used. The data showed that the heterochromatic matches were less reliable for the more saturated colors, violet and red, and also that the psychophysical methods used to obtain the matching data differentially influenced the results for the more saturated colors.

Black People↗
PubMed1978

Color-naming evidence for tritan vision in the fovea.

A color-naming task was used to assess color vision in the fovea and parafovea. Like traditional psychophysical procedures, color naming showed that short-wavelength vision is suppressed centrally. The anatomical and physiological mechanisms underlying tritan foveal vision are discussed.

Adolescent↗
PubMed1980

Chromoretinoscopy and its instrumentation.

Transmittance filters with selected dominant wavelengths, when placed in the light path between the light source of a retinoscope and the retinoscopist's eye, make possible a clinical measurement of the chromatic aberration of an eye. This kind of retinoscopy (chromoretinoscopy) also determines the approximate wavelength in focus in the retinal plane, when an eye is fixating an object at some distance. For laboratory purposes, these measurements can be considerably refined when a high intensity monochromator is used as the retinoscope's light source and care is taken to fix the subject's accommodation.

Color Perception↗
PubMed1980

The relationship between color discrimination and visual acuity in senile macular degeneration.

The course of ocular disease can be monitored by the assessment and measurement of a number of visual functions. In the clinical situation, visual acuity and color discrimination are obvious and simple functions to assess. The relationship between color vision and visual acuity in eye disease has generally been discussed only in qualitative terms. This paper examines the correlation between visual acuity and color discrimination for a number of subjects exhibiting varying degrees of severity of senile macular degeneration.

Aged↗
PubMed1980

The Bezold-Brücke phenomenon for purple colors.

A bipartite stimulus 2 degrees in diameter was used to study the Bezold-Brücke phenomenon for purple colors. A mixture of 460 nm and 667 nm in one half at a given luminance was matched with a mixture of the same two wavelengths at a luminance level 10 times higher. The hue of the 667-nm stimulus was not affected by the change in luminance. There is one mixture of red and blue which remains unchanged in hue as the luminance increases. Reddish purples shift toward red and bluish purples toward blue. These findings are consistent with a zone theory of color vision such as proposed by Adams.

Color Perception↗