stephen_m_kosslyn's picture
Founding Dean, Minerva Schools at the Keck Graduate Institute
robin_s_rosenberg's picture
Clinical Psychologist; Author, What's the Matter with Batman

Implications of Ivan Pavlov's Great Discovery

It's easy to imagine a politician's objecting to federal funds going to study how dogs drool. But failing to support such research would have been very short sighted indeed during the days of the great Russian physiologist Ivan Pavlov (1849—1936). As part of his Nobel Prize-winning research on digestion, he measured the amount of saliva produced when dogs were given food. In the course of this work, he and his colleagues noticed something unexpected: The dogs started to salivate well before they were fed. In fact, they salivated when they first heard the approaching footsteps of the person coming to feed them. That core observation led to the discovery of classical conditioning.

The key idea behind classical conditioning is that a neutral stimulus (such as the sound of approaching footsteps) comes to be associated with a stimulus (such as food) that reflexively produces a response (such as salivation)—and, after awhile, the neutral stimulus comes to elicit the response produced reflexively by the paired stimulus. To be clear about the phenomenon, we'll need to take a few words to explain the jargon. The neutral stimulus becomes "conditioned," and hence is known as the "conditioned stimulus" (CS), whereas the stimulus that reflexively produces the response is known as the unconditioned stimulus (UCS). And the response that is produced by the UCS is called the unconditioned response (UR). Classical conditioning occurs when the CS is presented right before a UCS, so that after a while the CS by itself produces the response. When this occurs, the response is called a conditioned response (CR). In short, at the outset a UCS (such as food) produces a UCR (such as salivation); when a CS (the sound of the feeder's footsteps) is presented before the UCS, it soon comes to produce the response, a CR (salivation), by itself.

This simple process gives rise to a host of elegant and non-intuitive explanations.

For example, consider accidental deaths from drug overdoses. In general, a narcotics user tends to take the drug in a specific setting, such as in his or her bathroom. The setting initially is a neutral stimulus, but after a person takes narcotics in it a few times, the bathroom comes to function as a CS: As soon as the user enters his or her bathroom with narcotics, the user's body responds to the setting by preparing for the ingestion of the drug. Specific physiological reactions allow the body to cope with the drug, and those reactions become conditioned to the bathroom (in other words, the reactions become a CR). To get a sufficient "high," the user must now take enough of the narcotic to overcome the body's preparation. But if the user takes the drug in a different setting, perhaps in a friend's bedroom during a party (and hence the new setting is not a CS), the CR does not occur—the usual physiological preparation for the narcotic does not take place. Thus, the usual amount of the drug functions as if it were a larger dose, and may be more than the user can tolerate without the body's preemptive readiness. Hence, although the process of classical conditioning was formulated to explain very different phenomena, it can be extended directly to explain why drug overdoses sometimes accidentally occur when usual doses are taken in new settings.

By the same token, classical conditioning plays a role in the placebo effect: For those of us who have regularly used analgesics such as ibuprofen or aspirin, such medicines begin to have their effects well before their active ingredients actually have time to take effect. How? From previous experience, the mere act of taking that particular pill has become a CS, which triggers the pain-relieving processes invoked by the medicine itself (and those processes have become a CR).

Classical conditioning also can result from an implanted defibrillator, or "pacemaker." When the heart beats too quickly, this device shocks it and thereby causes it to revert to beating at a normal rate. Until the shock level is properly calibrated, the shock can be very uncomfortable and can function as a UCS that produces fear as a UCR. Because the shock does not occur in a consistent environment, the person associates random aspects of the environment with it—which then function as CSs. And when any of those aspects of the environment are subsequently present, the person can experience severe anxiety, awaiting the possible shock and resulting reaction.

This same process explains why you would find a particular food unappealing if you happen to have eaten it and gotten food poisoning (and thus had significant gastrointestinal problems—the UCR to the UCS of tainted food). That type of food can thus come to function as a CS, and if you eat it—or even think about eating it—you may feel queasy, a CR. You may find yourself avoiding that food, and thus a food aversion is born. In fact, simply pairing pictures of particular types of food (such as French fries) with aversive photographs (such as of a horribly burned body) can change how appealing you find that food.

These examples should be sufficient to give you a sense of how the explanation for anticipatory salivation can be easily and simply extended to a wide range of phenomena. But, that said, we need to point out that Pavlov's original conception of classical conditioning was not quite right; he thought that sensory input was directly connected to specific responses, which led the stimuli to produce the response automatically. We now know that the connection is not so direct; classical conditioning involves many cognitive processes, such as attention and those that underlie the ability to interpret and understand. In fact, classical conditioning is a form of "implicit learning." As such, it allows us to navigate through life with less cognitive effort (and stress) than would otherwise be required. Nevertheless, this sort of conditioning has byproducts that can be powerful, surprising, and even sometimes dangerous.