Color blindness and color theory: some discriminations of normal and dichromatic subjects including a unilaterally color-blind person.
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Color vision deficits occur in 10% of the American white male population. Thus, color blindness may invalidate diagnostic hypotheses generated from Rorschach data. The Rorschach protocols of 43 white, college male color-blind subjects were compared to the protocols of normally sighted controls. The color-blind group manifested fewer pure "C" responses. No significant between group differences emerged for any of the other primary Rorschach color variables. Pure "C" responses rarely figure prominently in Rorschach evaluations, and the apparent lowered frequency of these responses by the color-blind is insufficient to warrant modification of current Rorschach practice. The data suggest that color blindness is unlikely to confound Rorschach assessment.
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Red/green color blindness, found in ~1 in 15 men, is caused by the expression of hybrid genes coding for visual pigments. Spectral information from site-directed mutagenesis and recombinant expression has led to the possibility of correlating individual genotypes with psychophysical measurements of the severity of the deficiency.
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The term "color blind" is encountered frequently in areas pertaining to health, commerce, art, and entertainment, but in these cases it is generally not appropriate. Complete color blindness or achromasy is rare, but weakness or absence of discrimination to certain colors can be found in at least 8% of the male population. The most useful description of these color defects is in terms of hue and saturation, thresholds of which can be plotted as polar coordinates on a circular diagram. Plotting color thresholds with the chromagraph reveals more clearly than other clinical systems the true nature of color defects, as well as some inconsistencies in the traditional terminology and test methods. Fifty strongly color-defective subjects were tested by five different methods and the results compared. Normal values are also indicated.
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Cortical color blindness, or cerebral achromatopsia, has been likened by some authors to "blindsight" for color or an instance of "covert" processing of color. Recently, it has been shown that, although such patients are unable to identify or discriminate hue differences, they nevertheless show a striking ability to process wavelength differences, which can result in preserved sensitivity to chromatic contrast and motion in equiluminant displays. Moreover, visually evoked cortical potentials can still be elicited in response to chromatic stimuli. We suggest that these demonstrations reveal intact residual processes rather than the operation of covert processes, where proficient performance is accompanied by a denial of phenomenal awareness. We sought evidence for such covert processes by conducting appropriate tests on achromatopsic subject M.S. An "indirect" test entailing measurement of reaction times for letter identification failed to reveal covert color processes. In contrast, in a forced choice oddity task for color, M.S. was unable to verbally indicate the position of the different color, but was surprisingly adept at making an appropriate eye movement to its location. This "direct" test thus revealed the possible covert use of chromatic differences.
BACKGROUND: Color blindness is a common hereditary X-linked disorder. OBJECTIVE: To investigate whether color blindness affects the ability to detect the presence of blood in body fluids. METHODS: Ten color-blind subjects and 20 sex- and age-matched control subjects were shown 94 photographs of stool, urine, or sputum. Frank blood was present in 57 (61%) of the photographs. Surveys were done to determine if board-certified internists had ever considered whether color blindness would affect detection of blood and whether an inquiry on color blindness was included in their standard medical interview. RESULTS: Color-blind subjects were significantly less able to identify correctly whether pictures of body fluids showed blood compared with non-color-blind controls (P =.001); the lowest rate of correct identifications occurred with pictures of stool (median of 26 [70%] of 37 for color-blind subjects vs 36.5 [99%] of 37 for controls; P<.001). The more severely color-blind subjects were significantly less accurate than those with less severe color deficiency (P =.009). Only 2 (10%) of the 21 physicians had ever considered the possibility that color blindness might affect the ability of patients to detect blood, and none routinely asked their patients about color blindness. CONCLUSIONS: Color blindness impairs recognition of blood in body fluids. Color-blind individuals and their health care providers need to be made aware of this limitation.
A red-green color blindness was studied in four families. All the carriers of the gene (mothers and sisters of the color blind individuals) had normal color vision. The color blind individuals were protanomalous or deuteranomalous. No protanopia or deuteranopia was found in the subjects who have been studied.
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