Story of Psychology - Morton Hunt [163]
As soon as a dog had food in its mouth, its saliva began to flow; since this was a response that required no training, Pavlov called the food an “unconditioned stimulus” and the salivary response an “unconditioned reflex.” The matter to be studied, however, was the link between a neutral stimulus and the same reflex. Typically, the experimenter, out of sight so as not to be a signal to the dog, would make a sound—ring a bell, buzz a buzzer—and would cause food to drop into the bowl anywhere from five to thirty seconds later. At first, the sound of the bell or buzzer would produce only a normal reflex—the pricking-up of the dog’s ears—but no salivary response. But after a number of these sequences, the sound alone would cause the dog’s saliva to start flowing. In Pavlov’s terms, the sound had become a “conditioned stimulus” to salivation, which had become a “conditioned reflex” to the sound.
Pavlov and his assistants ran many variations of this experiment. Instead of a sound, they would flash a light or rotate an object the dog could see through the window, manipulate apparatus that touched the dog or tugged on a part of its harness, change the length of time between the neutral stimulus and the delivery of food, and so on. In all cases, neutral stimuli could be made into conditioned ones, but with varying degrees of ease; a neutral odor (not of food) might require twenty or more pairings to become a conditioned stimulus, while the rotation of an object in the dog’s view might take only five pairings, the sounding of a loud buzzer only one.11
A psychologist would have called the conditioning process associative learning, but Pavlov explained it in physiological terms. Acknowledging indebtedness to his mentor, Sechenov, and to Descartes, the first to offer a reflex theory, he theorized that an unconditioned response, such as salivating on taking food into the mouth, was a brain reflex: A direct connection existed between the sensory and motor nerves in the spine or lower brain centers. In contrast, a conditioned response, such as salivating at the sound of a bell or other formerly neutral stimulus, was the result of new reflexive pathways created by the conditioning process in the cortex of the brain.
Pavlov developed this theory of localized brain reflexes in great detail to fit his findings about conditioning. But it was largely ignored except in the Soviet Union, and in America was soon conclusively disproven by the psychologist Karl Lashley, who removed different areas and amounts of cortex from rats, then had them learn mazes, and found that their loss of ability to learn was related not to the destruction of any particular cortical area but to the total amount destroyed.12
The fate of Pavlov’s physiological theory, however, in no way diminished the enthusiastic acceptance of his laboratory data and laws of conditioning as a major addition to psychological knowledge. These were some of his more noteworthy findings:
Timing: The sequence of the stimuli is critical. Only if the neutral stimulus precedes the unconditioned reflex does it become a conditioned stimulus, capable of eliciting the reflex. In one experiment, an assistant gave a dog food and five to ten seconds later turned on a loud buzzer; even after 374 such pairings, the buzzer alone did not bring about salivation. When he sounded the buzzer before giving the dog food, a single pairing was enough to make it a conditioned stimulus.13
Extinction: Unlike an unconditioned