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Summary Article: Yerkes, Robert Mearns (1876–1959)
from The Corsini Encyclopedia of Psychology and Behavioral Science

Robert Mearns Yerkes studied at Harvard University and received a doctorate in psychology in 1902. He held positions at Harvard and the University of Minnesota before he settled at Yale University in 1924, where he remained for 20 years. Yerkes and E. L. Thorndike were pioneers in the experimental study of animal behavior, following the traditions of C. Lloyd Morgan and George Romanes, the founders of comparative psychology.

Yerkes began his animal studies in 1900 and took charge of comparative psychology at Harvard in 1902. His research included a wide range of animals. He invented an experimental maze to study animal learning and the evolution of intelligence through the animal species. Yerkes was associated with the first primate laboratory at Yale University, where he was the director from 1929 to 1941. The laboratory was later transferred to Orange Park, Florida, and is now the Yerkes Regional Primate Center at Emory University in Atlanta, Georgia.

Out of his work in comparative psychology and animal behavior Yerkes formulated methods and techniques to test intelligence, monochromatic light to study color vision, and multiple-choice tests to measure concept formation. From his experiments he formed a theory that is called the Yerkes-Dodson law. It states that there is an optimal level of arousal for tasks, and that moderate levels of motivation facilitate problem solving and change. If stress is too high, the individual may not process relevant cues for learning; if it is too low, irrelevant as well as relevant cues will be processed indiscriminately.

Later Yerkes was interested also in human learning, and he developed a revision of the Stanford-Binet Intelligence Scale called the Point Scale. During World War I, Yerkes was chief of a group of psychologists who developed measures of abilities for assignments of army recruits to military positions and duties. These tests were the Army Alpha and the Army Beta, which were used to classify some 1.75 million individuals.

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