Psychology is defined as "the scientific study of behavior and mental processes". Philosophical interest in the human mind and behavior dates back to the ancient civilizations of Egypt, Persia, Greece, China, and India. Psychology as a field of experimental study began in 1854 in Leipzig, Germany when Gustav Fechner created the first theory of how judgments about sensory experiences are made and how to experiment on them. Fechner's theory, recognized today as Signal Detection Theory foreshadowed the development of statistical theories of comparative judgment and thousands of experiments based on his ideas (Link, S. W. Psychological Science, 1995). Later, 1879, Wilhelm Wundt founded in Leipzig, Germany, the first Psychological laboratory dedicated exclusively to psychological research. Wundt was also the first person to refer to himself as a psychologist. A notable precursor of Wundt was Ferdinand Ueberwasser (1752-1812) who designated himself Professor of Empirical Psychology and Logic in 1783 and gave lectures on empirical psychology at the Old University of Münster, Germany. Other important early contributors to the field include Hermann Ebbinghaus (a pioneer in the study of memory), William James (the American father of pragmatism), and Ivan Pavlov (who developed the procedures associated with classical conditioning). Soon after the development of experimental psychology, various kinds of applied psychology appeared. G. Stanley Hall brought scientific pedagogy to the United States from Germany in the early 1880s. John Dewey's educational theory of the 1890s was another example. Also in the 1890s, Hugo Münsterberg began writing about the application of psychology to industry, law, and other fields. Lightner Witmer established the first psychological clinic in the 1890s. James McKeen Cattell adapted Francis Galton's anthropometric methods to generate the first program of mental testing in the 1890s. In Vienna, meanwhile, Sigmund Freud developed an independent approach to the study of the mind called psychoanalysis, which has been widely influential. The 20th century saw a reaction to Edward Titchener's critique of Wundt's empiricism. This contributed to the formulation of behaviorism by John B. Watson, which was popularized by B. F. Skinner. Behaviorism proposed emphasizing the study of overt behavior, because that could be quantified and easily measured. Early behaviorists considered the study of the "mind" too vague for productive scientific study. However, Skinner and his colleagues did study thinking as a form of covert behavior to which they could apply the same principles as overt (publicly observable) behavior. The final decades of the 20th century