Several years before Watson’s formal founding of the school of behaviorism, many U.S. psychologists with strong leanings toward behaviorism insisted that psychology be defined as the science of behavior. Also, several Russians whom Sechenov had influenced were calling for a completely objective psychology devoid of metaphysical speculation. It was Sechenov’s discovery of inhibitory processes in the brain that allowed him to believe that all behavior, including that of humans, could be explained in terms of reflexes. During his research on digestion, Pavlov discovered “psychic reflexes” (conditioned reflexes), but he resisted studying them because of their apparent subjective nature. Under the influence of Sechenov, however, he was finally convinced that conditioned reflexes could be studied using the objective techniques of physiology. Pavlov saw all behavior, whether learned or innate, as reflexive. Innate associations between unconditioned stimuli (USs) and unconditioned responses (URs) were soon supplemented by learned associations between conditioned stimuli (CSs) and conditioned responses (CRs). Pavlov believed that some stimuli elicit excitation in the brain and other stimuli elicit inhibition. The pattern of the points of excitation and inhibition on the cortex at any given moment was called the cortical mosaic, and it was this mosaic that determined an organ- ism’s behavior. If a conditioned stimulus that was previously associated with an unconditioned stimulus is now presented without the unconditioned stimulus, extinction occurs. The facts that spontaneous recovery and disinhibition occur indicate that extinction is due to inhibition. If stimuli that elicit excitation on one hand and inhibition on the other are made increasingly similar, experimental neurosis results. An organism’s susceptibility to experimental neurosis is determined by the type of nervous system it possesses. According to Pavlov, conditioned stimuli act as signals announcing the occurrence of biologically significant events; he called such stimuli the first-signal system. An example is when the sight of a flame announces the possibility of a
painful experience unless appropriate behavior is taken. Language allows symbols (words) to provide the same function as conditioned stimuli, such as when the word fire elicits defensive behavior. Pavlov called the words that symbolize physical events the second-signal system. Pavlov believed that his work on conditioned and unconditioned reflexes furnished an objective explanation for the associationism that philosophers had been discussing for centuries.