Pavlov and the Conditioned Response
Pavlov’s early work, for which he earned the Nobel Prize in medicine in 1904, was not in psychology. Instead, his research was concerned with digestive physiology, and many of his laboratory studies focused on the secretion of saliva in dogs. Pavlov knew from the start that salivation is triggered whenever food (especially dry food) is placed in the mouth. During his experiments, however, a new fact emerged: Salivation could be set off by a range of other stimuli as well, including stimuli that were at first totally neutral. Dogs that had been in the laboratory for a while would salivate in response to the mere sight of meat, or the sight of the dish that ordinarily held the meat, or even the sight of the person who usually brought the meat. Pavlov was intrigued by these effects because he realized that in these cases, the organism seemed to be developing new reflexes and changing its behavior in a fashion directly shaped by learning. He decided to refocus his research program to study this learning.
In his experiments, Pavlov created simple patterns for the animal to detect. For example, he would ring a bell and then give the animal food. Then, after a short wait, he would present another pair of stimuli: bell, then food. After another wait, he presented yet another pairing: bell, then food. After several such pairings, Pavlov observed what happened if the bell was Harnesssounded alone, without any food being given (Pavlov, 1927;Figure 7.3). The result was clear:
The dog salivatedinresponse to the bell.To describe this pattern, Pavlov distinguished two types of responses: An unconditioned response (UR) was a biologi-cally determined reflex, triggered by a certain stimulus inde-pendent of any learning. In Pavlov’s terms, the trigger for an unconditioned response was an unconditionedstimulus(US). In the procedure described, the unconditioned stimulus(the US) is food in the animal’s mouth; the unconditionedresponse (the UR) is salivation. The linkage that makes the US and so (in Pavlov’s terms) is not a product of the learning process called “conditioning”; that’s why the stimulus and response are said to be unconditioned.
The second type of response is a conditioned response (CR), and it is a product of learning. Like the UR, the CR is triggered by a specific stimulus, but it’s a stimulus that was neutral at the start of learning. In our example, this neutral stimulus is the bell, and it came to elicit the CR (salivation) only after several presentations in which this stimulus was followed by the US (food in the mouth). In Pavlov’s terms, the bell is a conditioned stimulus (CS)—a stimulus that’s initially neutral but becomes associated with the US during the experiment.
The relationships between US and UR, CS and CR, are summa-rized in Figure 7.4 and form the basis of the learning studied by Pavlov. In his honor, this type of learning is sometimes called Pavlovian conditioning, but it’s more commonly known asclassical conditioning.
Early research on classical conditioning focused on one condi-tioned response—salivation by dogs—and a narrow range of condi-tioned stimuli (the sound of bells—or in other experiments, the ticking of metronomes). Subsequent research, however, has made it plain that this form of learning occurs in a remarkable range of species and circumstances. Indeed, classical conditioning can be documented not just in humans but in species as diverse as ants and ers, cats and cockroaches, wolves and worms. By using the appropriate US, researchers have conditioned crabs to twitch their tail spines, fish to thrash about, and octopuses to change color. Responses conditioned in studies with humans include changes in heart rate or blood pressure (where the US is typically a loud noise or rap on the knee) and the reflexive eye blink (using a US of a puff of air on the open eye).
Outside of the laboratory, classical conditioning touches many aspects of our lives. We all tend to feel hungry at mealtime and less so in between; part of the reason is a conditioning process in which the CS is a particular time of day and the US is the presentation of food (which normally is paired with that time of day). Our emotional responses to certain songs, or certain smells, or even certain social situations can be understood in similar terms, and the response is likely to be the result of some previous pairing between these stimuli and some emotional experience. This type of learning is, for example, a plausible basis for some forms of anxiety as well as some phobias (Figure 7.5). Yet another example is sexual arousal, which can often be produced by an initially neutral word or gesture that has—through learning—acquired an erotic association. Clearly, then, classical conditioning is a process with wide application and great importance.