Color Blind People Research Articles

“Tho’ she kneel’d in that place where they grew…” The uses and origins of primate colour vision

The disabilities experienced by colour-blind people show us the biological advantages of colour vision in detecting targets, in segregating the visual field and in identifying particular objects or states. Human dichromats have especial difficulty in detecting coloured fruit against dappled foliage that varies randomly in luminosity; it is suggested that yellow and orange tropical fruits have co-evolved with the trichromatic colour vision of Old World monkeys. It is argued that the colour vision of man and of the Old World monkeys depends on two subsystems that remain parallel and independent at early stages of the visual pathway. The primordial subsystem, which is shared with most mammals, depends on a comparison of the rates of quantum catch in the short- and middle-wave cones; this system exists almost exclusively for colour vision, although the chromatic signals carry with them a local sign that allows them to sustain several of the functions of spatiochromatic vision. The second subsystem arose from the phylogenetically recent duplication of a gene on the X-chromosome, and depends on a comparison of the rates of quantum catch in the long- and middle-wave receptors. At the early stages of the visual pathway, this chromatic information is carried by a channel that is also sensitive to spatial contrast. The New World monkeys have taken a different route to trichromacy: in species that are basically dichromatic, heterozygous females gain trichromacy as a result of X-chromosome inactivation, which ensures that different photopigments are expressed in two subsets of retinal photoreceptor.

An Inexpensive, Pocket-size Meter for Measuring Growing Media pH

Abstract The pH of a plant growing medium is a major determinant of nutrient availability and plant growth (1), so monitoring the pH of growing media is an important management practice. The pH of growing media can be measured colorimetrically with test papers or indicator solutions (2, 4) or potentiometrically with a glass electrode pH meter (1, 2, 6). Colorblind people, estimated to be 10% of the male population, cannot use colorimetric methods (3).

Heredity of two types of normal colour vision.

THE anomaloscope is used to diagnose red and green colour blindness and its four or six sub-types. In the apparatus the lower half of a circular plane is illuminated by a yellow light of wavelength 589 mµ, and in the upper half red (670 mµ) and green light (546 mµ) are mixed. It is possible, by changing the proportion of red and green illumination, to make the two halves look the same; the proportion of red and green lights required is called the Rayleigh equation, which is accepted by individuals with normal colour vision, but colour blind people react in different ways. On the anomaloscope which I used (model II, Schmidt and Haensch, Berlin) it is possible to change the wavelength of the monochromatic yellow light to make it more and more yellow green, or more and more orange, while the red and green lights are shifted in a similar manner. Rayleigh equations can be found for these wavelengths. I have built up a system of nine equations with the yellow light varying from 574 mµ to 603 mµ.