![]() ![]() Helmholtz (1866) had tentatively proposed that color blindness could manifest itself in three forms-red, green, or violet blindness-depending on the missing type of color receptor (one for red, one for green, and one for violet). Holmgren's wool test is based on the principles of Helmholtz's theory of color vision. Variants of this test were devised by Holmgren (1877) using skeins of wool by Abney (1906), Oliver (1902), and Edridge-Green (1920) using small beads or pellets and by Fridenberg (1903) using small square pieces of colored cardboard. The task was performed by inspection and without color naming. The next advance in testing was made by Seebeck (1837), who required the observer to choose from a wide range of colored samples those that matched or most closely resembled a selected test sample. Dalton (1798) gave a detailed description of his own perceptions and those of his brother (both protanopes) and of some 20 other persons. This was the method employed by Turberville (1684) and by several subsequent investigators. ![]() One of the earliest methods used to test color vision was to compare the individual's color naming of everyday objects with that of a normal person. ![]()
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