TYPES OF COLOR BLINDNESS: HOW THEY AFFECT TEACHING AND LEARNING

Many educators and students use color coding in a wide range of applications, for instance, to highlight important information in a text in a preferred color, or to alternate colors to differentiate varied topics within a paragraph. Many who employ color coding effectively, however, may not be aware that all individuals do not process all colors equally.

Nearly all color deficiency is hereditary, congenital and permanent. It is extremely rare to be absolutely ³color blind², (experiencing monochromasy, the complete absence of any color sensation), thus the term ³color blind² generally is inaccurate. Inherited color deficiency is most common, affects both eyes, and does not worsen. Although there is no cure for hereditary color vision deficiency, individuals may be taught to recognize colors by other means, such as by brightness. Those with mild color deficiencies learn to associate colors with certain objects and usually are able to identify color as well as those who view colors normally. However, the color deficient are unable to appreciate color in the same way as those with normal color vision might appreciate the contrasts of color in a sunset.

Approximately 8% of males and 0.5% of females are color deficient. This is due to chromosomal differences in males and females. Females have two x-chromosomes and men have only one x-chromosome and one y-chromosome. If a male¹s x-chromosome is color defective, he will be color deficient, whereas a female must inherit color deficiency on both x-chromosomes to be considered color deficient.

Individuals begin to perceive visually when light stimulates the retina, which is composed of rods and cones. Although rods, located in the peripheral retina, provide for night vision, they are unable to facilitate perception of color. We have three color detectors in the retina, the cones, each tuned to a certain frequency range of the visible spectrum. All the colors we see we derive by combining those three signals. Located in the center of the retina, cones are not useful in night vision but do allow for perception of color during daylight. Each cone contains a light sensitive pigment which relates to a range of wavelengths (the visible spectrum being 400 to 700 nanometers). Genes code for these pigments, but if the coding instructions are inadequate, the cones will be extraordinarily sensitive to certain wavelengths of light, resulting in color deficiencies in those wavelengths. The ability of the individual to perceive visible colors accurately depends on the degrees of sensitivity to the ranges of wavelengths.

With protanomaly, more commonly called ³red-weakness², pigments are shifted in hue from red, orange, yellow, and yellow-green toward a green color. These colors also appear paler to the color deficient, whereas, those who are deuteranomalous are considered ³green weak², and are poor at discriminating small differences in hues of red, orange, yellow and green. It is difficult for this type of color deficient individual to name many hues accurately, as most colors appear shifted toward the color red. In contrast to those who are protoanomalous, deuteranomalous individuals do not have a problem with loss of brightness.

It is possible to test for color blindness using the Isihara test. It utilizes a series of pseudoisochromatic plates, meaning that the colors appear to be in the same family but may not be. On these plates, numbers or letters are printed in dots of primary colors surrounded by dots of secondary colors. Figures are discernable by individuals with normal color vision, while those who struggle to notice the figures would be considered color deficient.

Then, there are some students who experience difficulty when attempting to comprehend information presented in low contrast such as grey pencil on white paper or in a black and white contrast. However, those same students more easily may comprehend the identical information when presented in bright colors. For instance, a math student unable to grasp the concept of intersecting planes presented in black and white (Fig. 1) may better grasp and recall the same concept when presented in color (Fig. 2).

Fig. 1	Fig. 2

Instructors may convey concepts more effectively by experimenting as to which colors facilitate learning and memory for their students.

BIBLIOGRAPHY

Baird, J. W. (1905). Colour Sensitivity of the Peripheral Retina, Carnegie Institute, Washington.

Bowditch, H., ³Red-Green Colour-Blindness in Three Allied Families,² Journal of Heredity, 3, (13), 139-142.

Collins, M. (1925). Colour-Blindness. New York: Harcourt, Brace & Company, Inc.

Dowling, John E. (1987). The Retina: An Approachable Part of the Brain. Boston: The Belknap Press of Harvard University Press.

Krauskopf, C. C. (1901) "Some Results of Sight Tests Applied to Chicago School Children," Trans. of the Ill. Soc. for Child-Study, 6 (2), see also Child Study Monthly and Journal of Adolescence, 6: 283.

Mueller, C. G. and R. M. (1996). Light and Vision. New York: Time Inc.

Sacks, Oliver (1996). The Island of the Colorblind. New York: Alfred A. Knopf, Inc.

Whipple, G. M. (1914). Manual of Mental and Physical Tests, Vol. X, Baltimore, MD.

Lyndsey Gue is a student majoring in biopsychology at the University of Maryland, Baltimore County, entering into medical school, who also works as a commissioned artist. Her most recent effort, a 20¹ by 8¹ mural, is on view at the Women¹s Health Center in Franklin Square Hospital in Baltimore, Maryland. She has studied the effects of color extensively, and applied the results of her research in her artwork.