American psychologist who made important contributions to the fields of comparative animal psychology, particularly in the areas of animal intelligence and behavior.
Robert Yerkes was born in Pennsylvania, and was educated at Harvard University, where he received his doctorate in psychology in 1902. He served as professor of psychology at Harvard, the University of Minnesota, and Yale University, and as a member of the National Research Council. In 1919, Yerkes founded the Yale Laboratories of Primate Biology and served as its director from 1929 to 1941, when the lab was moved to Orange Park, Florida. A year later, it was renamed the Yerkes Laboratories of Primate Biology. A pioneer in the field of comparative psychology, Yerkes studied the intelligence and behavior of many forms of animal life, from jellyfish to humans, but he focused most of his attention on primates. Among his findings were the discovery that chimpanzees imitate both each other and human beings, and the observation that orangutans can pile boxes on top of one another to reach food after seeing this demonstrated, thus transferring this experience to other learning problems.
Yerkes also worked on the Yerkes-Dodson Law, which states that for every task there is an optimum level of motivation, and that motivation that is too strong can actually interfere with the ability to perform a difficult task. Yerkes also pioneered the use of monochromatic light to study color vision in animals. In 1911, he developed the first multiple-choice test for animals, designed to test abstraction abilities. A row of nine or fewer boxes were shown to the animal, which had to determine which of the open boxes had food in it and then remember that box in subsequent rounds of testing.
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