According to standard histories, psychology emerged as an independent discipline in 1879, when Wilhelm Wundt (1832-1920) founded a psychology laboratory at the University of Leipzig, Germany. In his work, Wundt assumed that the study of conscious or subjective mental life was the appropriate subject matter for psychology. As part of his study of mental life, Wundt conducted experiments in an area close to what we would now call sensation and perception. Wundt believed that by understanding mental life, we could come to understand the full range of the human condition, including human culture. Prior to that time, people may well have studied sensory physiology and reflexes, engaged in discussions about moral philosophy and conduct, engaged in philosophical discussions about the nature and limits of knowledge, or even carried out demonstrations similar to Wundt's. However, Wundt is generally credited with launching psychology as a distinct branch of experimentally based, scientific study, idiosyncratic though it was.
Many individuals went to Leipzig to study the "new psychology" with Wundt and then went on to start programs at other universities. Among those who studied at Leipzig was the Englishman E. B. Titchener (1867-1927), who emigrated to the United States and started his own psychology program at Cornell University in Ithaca, New York, in 1892. Titchener called his approach "structuralism." Following Wundt, Titchener assumed that the appropriate subject matter for psychology was conscious, subjective mental life. For Titchener, the elements of mental life were our sensations, images, and feelings. These elements were to be studied by carefully drawing inferences from participants' introspective reports and reaction times. Participants needed to be adults--children were not suitable. Participants also needed to be "properly trained"--they needed at least 10,000 closely supervised training trials. Given appropriate training, for example, participants could then be expected to introspectively discern as many as 42,415 different sensations, and Titchener could infer which of those sensations were higher or lower in the structure of consciousness. Throughout, however, participants needed to be careful to report the stimulus as a primitive, fundamental phenomenon, and not commit the "stimulus error" by interpreting the stimulus.
Even though structuralism did become reasonably influential in the United States, many questioned whether it had practical implications, such as for educating children, training the workforce, or managing behavior in any general sense. Accordingly, an alternative to structuralism emerged in the late 1800s and early 1900s in the United States called "functionalism." Functionalists employed some of the same research methods as had structuralists but emphasized the function of conscious mental phenomena, such as how they aided adaptation. For example, functionalists might use reaction times to study how children's conscious mental phenomena developed over time, so that educational practices could be properly tailored to their development.
Two difficulties that arose in connection with both structuralism and functionalism were the lack of reliability and the lack of agreement. Introspection as a method was particularly problematic. For instance, concerning the lack of reliability, research findings with the introspective method were not often replicated with other participants or in other laboratories, despite the emphasis on properly trained participants. Similarly, concerning the lack of agreement, it was not abundantly clear what psychologists were actually talking about when they debated whether there was a difference between introspective reports about the "texture" of an image and a sensation. As a result, psychology lurched back and forth between many esoteric discussions that failed to convince the general public of its practical value.
The Rise of Behaviorism
Beginning in the second decade of the 20th century, John B. Watson (1878-1958) argued ferociously against both structuralism and functionalism. In a now classic article, Watson (1913) asserted that neither was effective as a science and that the time had come for psychology to take its place as a legitimate natural science. It could do so by discarding its long-standing concern with conscious mental functioning as a subject matter and introspection as a method. In Watson's view, mental life as traditionally conceived simply did not exist. Rather, psychology should embrace behavior as its subject matter and rely on experimental observation of that subject matter as its method. He called his viewpoint behaviorism. It was objective as opposed to subjective; it borrowed measurement and analytical techniques from "animal psychology" and reflexology and then applied them to adaptive forms of behavior. It insisted on analyzing behavior at a detailed and, if necessary, sequential level--what we would now call a molecular level--instead of accepting it at a large-scale and integrated level--what we would now call a molar level. By emphasizing observability, it avoided problems inherent in introspective reports, namely, the lack of reliability and the lack of agreement. The principal unit of analysis for Watson was the "habit," defined as the coordinated and consistent act that develops in a given situation through repetition, rather than some supposed phenomenon from mental life. He applied his analysis to everything from human emotional responses to language. Today we call Watson's viewpoint classical S-R behaviorism. Classical behaviorism may be said to represent the first phase of the "behavioral revolution."
Despite the importance of Watson's contributions, two problems remained. One was the apparent spontaneity of behavior: Some responses seemed to develop without a characteristic stimulus evoking them. A second problem was the variability of behavior. Even when a characteristic stimulus preceded responses, the topography and frequency of the responses often differed significantly. As a result of such problems, by 1930 many researchers and theorists began to seek ways to modify classical S-R behaviorism.
At issue was how to do so. One approach that proved popular was to insert intervening, "organismic" variables between stimulus and response. The function of these variables was to mediate the relation between stimulus and response, thereby accommodating the previously mentioned concerns about spontaneity and variability. In this mediational approach, external stimuli (S) are held to activate some intervening, internal process or entity (0) that is causally connected in a complex but systematic way to an eventual response (R), and the mediating process or entity (the aforementioned 0 variable) is taken as the proper focus of psychological science, rather than the response itself. In other words, the response is functionally related to the mediator, rather than the environment, because the organism is in direct contact with only the mediator, rather than the environment. Early examples of these mediating organismic variables were response tendencies, motives, and purposes. Later examples …