Story of Psychology - Morton Hunt [164]
Generalization: If a dog was presented with a stimulus similar to, but somewhat different from, a stimulus it had become conditioned to—for instance, a tone higher or lower than the one paired with food—the dog would salivate, but less strongly than in response to the conditioned tone. The greater the difference between tones, or between any conditioned stimulus and a related stimulus, the weaker the response. The dog was, in effect, generalizing from its experience and expecting similar experiences to yield similar results.
Differentiation: After a dog had been conditioned to salivate on hearing a given tone and also on hearing another tone some notes lower, if the first tone was then always reinforced by food but the second one never was, the dog would gradually cease to salivate in response to the second tone. The dog had learned to “differentiate”—the term more often used by English and American psychologists is “discriminate”—between the stimuli.
Experimental neurosis: In seeking to determine the limits of his dogs’ ability to discriminate, Pavlov unexpectedly precipitated in them something resembling a nervous breakdown. In one historic study, a dog learned to discriminate between a circle flashed on a screen, always followed by food, and an elongated ellipse flashed on the screen, never followed by food. When the dog’s salivating at the sight of the circle and failure to salivate at the sight of the ellipse were well established, the assistant began changing the shape of the ellipse, making it ever more nearly circular. The dog kept learning to discriminate between the circle and the rounder ellipses until the ratio of the axes of the ellipse was 7:8. The assistant then tried an even rounder ellipse whose axes had a ratio of 8:9, but at that point, Pavlov later wrote,
the hitherto quiet dog began to squeal in its stand, kept wriggling about, tore off with its teeth the apparatus for mechanical stimulation of the skin, and bit through the tubes connecting the animal’s room with the observer, a behavior which never happened before. [Later,] on being taken into the experimental room the dog barked violently, which was also contrary to its usual custom; in short, it presented all the symptoms of a condition of acute neurosis.14
Only after long rest and careful treatment did the dog recover enough to tolerate experiments in easier differentiations.
286 The Story of Psychology
Pavlov believed that he had identified the fundamental unit of learning in animals and human beings. All learned behavior, he said, whether acquired in school or outside it, was nothing but “a long chain of conditioned reflexes” whose acquisition, maintenance, and extinction were governed by the laws he and his assistants had discovered. His ideas profoundly influenced Russian psychology from early in the century until the 1950s, but in the West remained largely unknown for some years, even though Pavlov had mentioned conditioning in his 1904 Nobel award address.
In 1908 Robert Yerkes (who would later direct the development of the Army Alpha and Beta) and a colleague learned about Pavlov’s work from German journals, corresponded with him, and published a brief article in the Psychological Bulletin describing his method and main findings. They emphasized the usefulness of his research methods but failed to predict the effect the concept of the conditioned reflex would have on American psychology.15
But in 1916 John B. Watson—whom we are about to meet—began to spell out how Pavlovian conditioning enlarged the behaviorist theory of psychology, and a few years later he termed the conditioned reflex “the keystone of the arch” of behaviorist theory and methodology.16 In
1927 Pavlov’s book, Conditioned Reflexes, appeared in English, and from then on behaviorist psychologists rapidly