Ninth Edition CoverGraziano & Raulin
Research Methods (9th edition)

Ivan Petrovich Pavlov (1848-1936) was a Russian physiologist, who was deeply influenced by Darwin’s work and may have turned to the study of animal physiology because of it. 

From 1897 to 1936, with his extraordinary intellect and outstanding devotion to selfless hard work, Pavlov supervised a large laboratory of some 150 researchers and produced more than 500 scientific papers (Schultz & Schultz, 2008). One of his most important books was Conditioned Reflexes (1927). This work presented the basic experimentally-derived concepts that would later provide some of the underpinnings for the behavioral work of  Watson, Hull, and Skinner. Thus, Pavlov helped to define the direction of behaviorism, and behaviorism became the dominant school of psychology for some 60 years, from the 1920s to the 1980s. 

By 1904, when he was awarded the Nobel Prize for his work in the physiology of digestion, Pavlov had become world famous. He had not only discovered basic knowledge about animal physiology, but had also created many new surgical procedures, which were used around the world. His three major areas of research were (1) the function of nerves tending the heart, (2) the physiology of digestion, and (3) the conditioned reflex.

In his laboratory, Pavlov insisted on strict standards of careful procedures to maintain his objective studies. He was very critical of the psychologists of the day, who continued such non-objective procedures as Wundt’s and Titchener’s introspection. His experiments were carefully conducted and replicated to be sure the findings held up.

Pavlov credited Darwin for his early influence and Thorndike for creating objective methods and concepts to study animal behavior. Major concepts developed by Pavlov in his studies of the conditioned reflex (now referred to as classical conditioning, Pavlovian conditioning, or respondent conditioning) include:

  1. The unconditioned reflex is a physiological stimulus-response relationship that occurs naturally with no learning trials necessary. This occurs when an unconditioned stimulus is presented and it elicits an unconditioned response. An unconditioned stimulus is a stimulus that has an effect on behavior in which no learning trials are necessary. An unconditioned response is a response that occurs to a particular stimulus, in which no learning trials are necessary. For example, food (unconditioned stimulus) presented to an animal elicits salivation (unconditioned response). When a neutral stimulus (the conditioning stimulus), such as a bell or a light, is paired repeatedly with the unconditioned stimulus (the food), the animal begins to salivate to the previously neutral stimulus--the bell or light. The pairing of the conditioning stimulus with the unconditioned stimulus and the resulting unconditioned response, is the process of reinforcement. The reflex that results--for example, salivation to the bell or light--is called the conditioned reflex. This, in the Pavlovian model, is one kind of learning. In this way, many new behaviors are learned (called acquisition).
  2. A conditioned reflex is weakened and eventually lost when the conditioned stimulus is repeatedly presented without pairing it with the unconditioned stimulus. For example, the light is repeatedly presented, salivation occurs each time, but the food is never paired with it. This weakening process is called extinction. Essentially, extinction is a process of withholding reinforcement. Through extinction, previously conditioned behaviors are lost. Thus, animal behavior is flexible, with new reflexes being constructed and, when no longer useful, weakened and lost.
  3. Once conditioning occurs, there can be generalization of the conditioned response to a range of similar stimuli. This range is called a stimulus generalization gradient. For example, a child fearful of dogs may also respond with fear to other furry animals. Likewise, the magnitude of the response varies depending upon the similarity to the conditioned stimulus, becoming weaker as the stimulus becomes more dissimilar to the original conditioned stimulus.
  4. Differentiation occurs when the animal learns to respond to a limited range of stimuli, while ignoring other stimuli farther along the gradient.

The implications of Pavlov’s discoveries for animal behavior in the wild, for human social behavior, and for abnormal functioning were enormous. At first, American psychologists, still largely involved in introspection, were not responsive to Pavlov’s work. But a small group who studied animal behavior saw the relevance of Pavlov’s research, which became a powerful influence on the development of behaviorism in the United States. B. F. Skinner, for example, was directly influenced by Pavlov’s work. (Note the fairly direct line of influence: Darwin -> Romanes and other animal psychologists ->Thorndike -> Pavlov-> Skinner). 

The discoveries of conditioning also influenced clinical psychology and psychiatry. Pavlov is one of the giants in the history of psychology.

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