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Color Vision
... The chromatic discrimination impairment can vary from a very weak loss of discrimination mediated by the L-cone or M-cone -anomalous trichromacy -to total loss of discrimination -dichromacy (Motulsky, 1988;Neitz and Neitz, 1995;Neitz et al., 2004;Deeb, 2005). Two post-receptoral channels exclusively carrying L-and M-cone information building physiologically opponent center-surround input processing in which signals from the L-and M-cones are antagonists -often called red-green opponency (De Valois and Abramov, 1966;De Valois and Jacobs, 1968;Lee et al., 1989;Lee, 1996). The Parvocellular (PC) pathway is suggested to carry the color information to the visual cortex and the Magnocellular (MC) pathway the luminance information (Lee, 1996). ...
In congenital color blindness the red–green discrimination is impaired resulting in an increased confusion between those colors with yellow. Our post-receptoral physiological mechanisms are organized in two pathways for color perception, a red–green (protanopic and deuteranopic) and a blue–yellow (tritanopic). We argue that the discrimination losses in the yellow area in congenital color vision deficiency subjects could generate a subtle loss of discriminability in the tritanopic channel considering discrepancies with yellow perception. We measured color discrimination thresholds for blue and yellow of tritanopic channel in congenital color deficiency subjects. Chromaticity thresholds were measured around a white background (0.1977 u′, 0.4689 v′ in the CIE 1976) consisting of a blue–white and white–yellow thresholds in a tritanopic color confusion line of 21 congenital colorblindness subjects (mean age = 27.7; SD = 5.6 years; 14 deuteranomalous and 7 protanomalous) and of 82 (mean age = 25.1; SD = 3.7 years) normal color vision subjects. Significant increase in the whole tritanopic axis was found for both deuteranomalous and protanomalous subjects compared to controls for the blue–white (F2,100 = 18.80; p < 0.0001) and white–yellow (F2,100 = 22.10; p < 0.0001) thresholds. A Principal Component Analysis (PCA) found a weighting toward to the yellow thresholds induced by deuteranomalous subjects. In conclusion, the discrimination in the tritanopic color confusion axis is significantly reduced in congenital color vision deficiency compared to normal subjects. Since yellow discrimination was impaired the balance of the blue–yellow channels is impaired justifying the increased thresholds found for blue–white discrimination. The weighting toward the yellow region of the color space with the deuteranomalous contributing to that perceptual distortion is discussed in terms of physiological mechanisms.
The visual world offers a variety of information that enables animals to orient themselves to their surroundings. One specific feature of the visual information is the wavelength difference of light emittedfrom light sources or reflectedfrom objects. Under natural conditions, a general difference in the spectral composition of light is based upon the fact that light coming directly from light sources, e.g., the sun, sky, and moon, is characterized by its relatively high content of short wavelength (<450nm), whereas light reflected from natural objects such as leaves and soil lacks UV light and is dominated by green and yellow light (>450nm) (Figs. 1). The physical basis of these differences is the preferential absorption by pigment molecules, which—in contrast to atoms and small molecules—have resonances above 300 nm and shift the bulk of the reflected light into the green and orange region of the spectrum. In water, the wavelength range is compressed in the long-wavelength part of the spectrum due to water’s high absorption of red and infrared light (Fig. 1). But in water, too, direct light is relatively richer in shortwave light. Neglecting the finer differences in the spectral content of light, this general distinction between direct and reflected light could be the cue that allows an animal to differentiate such basically different habitats as open spaces, shadowed areas, spaces rich in food, hiding places, etc.
The article aims at presenting a comprehensive overview of studies on colour from the perspective of applied psychology and social sciences. It discusses major findings from the psychology of colour applied to marketing, business, politics and sports as well as problems connected with using color tests is psychological diagnosis. Moreover, an overview of particularly interesting colour studies on synaesthesia is presented related to cognitive and applied psychology as well as psycholinguistics. Finally, the most recent trends in investigations into applied colour psychology as well as potential directions for further research are discussed.
An important part of the complete television system is the viewer. His conscious response is the ultimate output of the total system. A summary is made of some of what is currently known of the way in which his responses are formed. This knowledge of the process of color perception is related to the characteristics of color television images.
Synopsis
A study is undertaken of the field excited in a semi-infinite cylindrical dielectric rod having small conductivity when plane harmonic electromagnetic waves are incident obliquely upon its end. All back-scattering and the complicated edge effects due to the end of the rod are neglected. Expressions for the normalized power absorbed in the rod are obtained by an approximation technique from the corresponding results for a similar rod whose conductivity is zero, assuming that the radiation through the walls of the rod may be ignored. Selected numerical results are presented and the relevance of these to models of a retinal rod of the human eye is discussed.
The author has selected resource material that focusses on color vision and the measurement and specification of the stimulus for vision, that is, photometry and colorimetry. References are marked E (elementary), I (intermediate), and A (advanced). Those references to be included in a Reprint Book are marked with an ().
The physiology of colour vision is reviewed in the light of recent neurophysiological and anatomical studies in vertebrate retinas. The physiological correlate of trichromasy is the existence of three classes of cone cells, each possessing exclusively one of three photopigments with maximum spectral sensitivity at either 440 nm, 540 nm or 570 nm. The electrical responses of single cells of the various types within the retina and lateral geniculate nucleus exhibit both spatial and chromatic coding which is opponent in character. The horizontal and amacrine cells show sophisticated responses which demonstrate their important roles in the processing of information about colour vision. Human abnormal colour vision is reviewed in the light of recent psychophysical studies. Red-green dichromasy is due to the absence of one of the two photopigments normally active in the red-green range of the spectrum. In the red-green anomalous trichromasies one of the photopigments active in that range is replaced by an abnormal photopigment although the spectral loci of the peak sensitivity of these photopigments and the shape of their absorption curves have not yet been accurately identified. The traditional association of mono-chromasy with a rod-only retina has been challenged by the finding of cone cells in histological preparation of eyes of achromats, and the psychophysical evidence that more than one receptor type participates in visual function. One of these receptor types is the normal rod but the other may be a normal blue-sensitive cone or a cone filled with rhodopsin, the rod photopigment.
1.1. The S-potentials recorded intracellularly from the mixed retina of both Acanthogobius flavimanus and Glossogobius olivaceus probably arise from the small horizontal cells situated directly below the layer of receptors.2.2. The L-responses hyperpolarize in response to light, regardless of stimulus wavelength, and the responses in photopic conditions are found to be subserved by a single photopigment with γmax = 584 nm.3.3. Together with L-response, C-response was recorded in these fishes.4.4. The present experiment cannot exclude the possibility that fishes must have two or more classes of receptors with different properties.
STABELL, U. & STABELL, B. Facilitation of chromatic cone activity by rod activity. II. Variation of chromatic-related cone activity. Scand. J. Psychol., 1971, 12, 168–174.–At the cone-rod break of the dark adaptation curve, the specific threshold was found to drop to lower intensity levels, while the threshold curves of fovea proceeded in one step only, confirming the suggestion that rods may facilitate chromatic-related cone activity.
Light isomerizes the chromophore of rhodopsin, 11-cis retinal (formerly retinene), to the all-trans configuration. This introduces a succession of unstable intermediates—pre-lumirhodopsin, lumirhodopsin, metarhodopsin —in which all-trans retinal is still attached to the chromophoric site on opsin. Finally, retinal is hydrolyzed from opsin. The present experiments show that metarhodopsin exists in two tautomeric forms, metarhodopsins I and II, with λmax 478 and 380 mµ. Metarhodopsin I appears first, then enters into equilibrium with metarhodopsin II. In this equilibrium, the proportion of metarhodopsin II is favored by higher temperature or pH, neutral salts, and glycerol. The change from metarhodopsin I to II involves the binding of a proton by a group with pK 6.4 (imidazole?), and a large increase of entropy. Metarhodopsin II has been confused earlier with the final mixture of all-trans retinal and opsin (λmax 387 mµ), which it resembles in spectrum. These two products are, however, readily distinguished experimentally.
PH has been completely unable to recognise faces since sustaining a closed head injury some four years ago, but can recognise familiar people from their names. His performance on face processing tasks is, however, comparable to that of normal subjects if explicit recognition is not required. Thus he can make same/different identity judgements more quickly for familiar than unfamiliar face photographs, and faster matching of familiar faces is only found for identity matches involving the face's internal features. When making semantic categorisation decisions to printed names he shows interference from distractor faces belonging to an incorrect category, even when the faces in each category are matched on physical appearance. When learning to associate the occupation or the name with photographs of faces, his performance is better with true (face and person's actual name or occupation) than untrue (face and another person's name or occupation) pairings. Covert recognition can also be demonstrated for faces of people PH has only met since his accident. These findings show that in prosopagnosia, much of the processing of familiar faces can remain intact despite absence of awareness that recognition has occurred.
The responses were recorded of single units in the visual cortex of anesthetized monkeys. The stimuli were brief flashes presented diffusely on the retina through five broad pass color filters in succession. The initial intensity of the flashes was high and nearly equal for the different colors, and the eye was maintained in a steady state of light-adaptation by diffuse white illumination. Of the single units which responded to light flashes, more than half did so to only one of the monochromatic flashes, or to a few adjacent on the spectrum. The response consisted of one or two spikes at all flash intensities. Units with similar response characteristics have not been reported in the geniculate, suggesting that these units are cells whose narrow spectral responsiveness is due to features of cortical organization. When the background illumination was switched off and the eye maintained in the dark for up to 10 min, the responses of most single units tested was unchanged, suggesting that they were connected solely with cone receptors. The responses of the same units to optic nerve stimulation suggested that they lay on a monosynaptic pathway with no evidence of convergence in the central nervous system.
The amount of color induced into a field of Illuminant A was determined for four inducing colors, red, yellow, green and blue, by having observers compare the induced color with a field of actual colored light. The results, given in C. I. E. values, show that the amount of color induced increases as the size of the inducing field is increased, as the luminance ratio between inducing and induced fields is increased, and, to a small extent, as the purity of the inducing color is increased.La quantitéde couleur induite dans un champ de l'étalon colorimétrique A fut mesurée pour quatre couleurs inductrices, rouge, jaune, verte et bleue, en faisant comparer aux observateurs la couleur induite avec un champ de lumière réellement colorée. Les résultats, donnés en valeurs C.I.E., montrent que la quantitéde couleur induite augmente avec la dimension du champ inducteur, avec le rapport des luminances entre champs induit et inducteur, et pour une faible part avec la puretéde la couleur inductrice.Indem die Beobachter die induzierte Farbe mit einem Feld, das mit einer reinen Farbe erleuchtet war, verglichen, wurde der Anteil der induzierten Farbe in einem Feld der Lichtart A für vier Farben, nämlich Rot, Gelb, Grün und Blau gemessen. Die Ergebnisse, die im C.I.E.-System dargestellt sind, zeigen, dass der Anteil der induzierten Farbe in der gleichen Weise ansteigt, wie die Grosse des induzierenden Feldes wächst, wie der Helligkeitsunterschied zwischen dem induzierenden und dem induzierten Felde zunimmt, und in geringem Masse wie die Reinheit der induzierenden Farbe grosser wird.
Fish were trained to jump at the correct (rewarded) one of two differently colored feeders and to avoid feeders of other colors and different shades of gray. It was found that the fish could discriminate the colors red, blue, yellow, and green both in the normal state and after complete section and regeneration of the optic nerve.When the color preferences were trained prior to optic nerve section, regeneration of the nerve resulted in reinstatement of the same color preferences, no relearning being necessary. Some of the implications regarding specificity of the optic fibers and factors governing their central synapsis in the optic tectum are discussed.
