Pavlovian Conditioning Pavlovian conditioning, or classical conditioning, is a form of learning. Learning is what happens when some past experience in your life alters your present behavior. In the case of Pavlovian conditioning, learning involves the association of some stimulus, such as a sound, a light, a smell, with the experience of either something good or something bad. When the stimulus reliably predicts that the good or bad thing is about to happen, then we learn that the stimulus is a predictor of that good or bad thing. That predictor then becomes a stimulus that allows us to prepare our bodies to deal with the good or bad thing that is about to happen. Pavlovian conditioning was of course discovered by Ivan Pavlov. Like so many other great discoveries in science, it was completely accidental. Pavlov was a Russian physiologist who was awarded the Nobel Prize in 1904 for his work in understanding the digestion of food. At the time of the discovery of Pavlovian conditioning, Pavlov's lab was engaged in studying the salivation reflex that occurs when we eat. Dogs had been prepared with a small vial attached to the side of the jaw. The duct from a salivary glad was surgically exposed and positioned so that the saliva that was produced by the gland would go into the small vial. Afterwards the vial would be removed and the amount of saliva was recorded. To produce the saliva, Pavlov's dog subjects were given "meat powder". After a few days of getting meat powder to produce saliva, the dogs did something that would change the history of psychology: The dogs began salivating BEFORE they were fed! As soon as they noticed the researchers coming to fetch them for the experiment, they would begin salivating. Anyone who has ever loved and fed a dog before, or even paid attention to their own bodies, knows that this happens. Whenever dogs (or any other critters) get exposed to some signal that they're about to get fed, they wag their tails, get excited, and salivate. However, this was a very surprising thing for all the physiologists in Pavlov's lab. Why did the dog start salivating when it had no food in it's mouth? And why did this odd behavior take a few days to develop? Pavlov hypothesized that the dogs were reacting to the expectation of being fed. That led to the question of how they learned that expectation. Pavlov hypothesized that the dogs were reacting to cues in their environment that signaled the arrival of food. He also hypothesized that any stimulus that the dogs could perceive could be used as a cue to predict the food. Thus we have the apocryphal story of Pavlov's dogs and the "bell". However, Pavlov did not use a bell as a stimulus. Instead, to test his hypothesis he used a ticking metronome, probably because that sound was very unlikely to have ever been heard by the dogs. The ticking sound was started, and the followed by meat powder. Sure enough, after a few of these pairings, just the sound of the metronome was enough to cause the dogs to salivate. Pavlov went on to characterize in great detail this new learning phenomenon, which he referred to as a "conditional reflex". Pavlov's understanding of conditional reflexes was in the context of stimulus-response theory, where behaviors are the result of stimuli causing responses to occur. Think of the reflex action of a doctor tapping your patellar tendon with a rubber hammer (the stimulus) and causing the leg to flex forward (the response). With his new theory, Pavlov created an elegant way for stimuli and responses to be altered based on experience. In Pavlov's framework, the meat powder is called an "unconditional stimulus" (US) and salivation is the "unconditional response" (UR) to the meat powder US. US's elicit UR's and that is usually represented like this: US -------> UR The US-UR relationship is prewired into the brain of the person or animal, and is not learned. Thus, dogs don't have to learn to salivate when they get food. That's a reflexive action that results from the way their nervous systems are wired. What happens in Pavlovian conditioning is that a neutral stimulus (NS) gets paired with a US. When we say "paired" we mean that the NS occurs first, followed by the US: NS ------> US ------> UR Over time, this neutral stimulus starts to become meaningful to the animal, because it reliably predicts the coming of the US. This is the key to Pavlovian conditioning. The NS becomes important because it allows the animal to EXPECT the US. Thus, over time, if the NS becomes a reliable predictor of the US, it will become a cue to the animal that it needs to prepare for the US and the UR that follows the US. Here's the most important part: When the NS acquires this predictive value, it goes from being a meaningless neutral stimulus to a meaningful "conditional stimulus" (CS). A conditional stimulus is one that an animal has learned is a reliable predictor of some US. As a result, the animal learns to elicit a response to the CS, in order to help it prepare for the oncoming US-UR. When the animal starts eliciting this response to the CS, we call this response the "conditional response" or CR. When the CS comes to elicit the CR like this: CS ------> CR We say that conditioning, or learning has occured. In the case of Pavlov's dogs, the CR was salivation, which happens to be the same as the UR. The CR is often, but not always, the same as the UR. The key to figuring out if the CR will be like the UR is to understand that the CR is always about helping the person or animal PREPARE for the expected US that is coming. The CS tells the critter that the US is coming, therefore the critter prepares for that US by responding with the CR. A classic model of Pavlovian conditioning used nowadays in research is fear conditioning in rats. A rat is put into a box called a Skinner box. On one side of the Skinner box is a small light. The floor of the box is made up of steel rods spaced about a half inch apart. Electric currents are fed to the steel bars to deliver foot shocks to the rat. The shocks are very uncomfortable, but do not cause any damage to the rat. Now imagine that the rat is placed into this Skinner box. A few minutes later, the light comes on for five seconds, goes off, followed by a two second foot shock. This process repeats 10 more times. By the time it ends, the rat will have developed a fear of the light coming on. That fear will have developed because the light (CS) has come to signal the coming of the foot shocks (US) which of course produce fear (UR). The response to the light CS, however, will be FREEZING, where the rat remains completely motionless until it feels safe again. This freezing behavior is the CR that we always see when doing fear conditioning in rats. Thus, instead of squeaking and jumping around like they do when exposed to the foot shock US, the CR is freezing, which is a response to prepare them for the fear of the footshock. The process of presenting the CS, then the US, then the UR so the critter learns that the CS is a reliable signal of the US is called ACQUISITION. At the start of acquistion, the animal or human of course does not respond to the CS, which starts off as neutral. Over the repeated presentations (usually referred to as trials) during acquisition, the animal acquires the relationship between the CS and US. What happens if you stop delivering the US, the food or the foot shock? If the animal starts experiencing the CS not followed by the US, then over time the CR response will fade away, because the CS no longer signals the coming of the US. This process of "unconditioning" the CS-US relationship is called extinction. Extinction is much more than a simple process of forgetting. It involves learning yet another new thing about the stimulus that was the CS. Pavlovian conditioning is an extremely powerful and elegant process we all have built into our brains. It is the mediator for so many of our most basic behaviors, and can be used to understand everything from certain psychological disorders to training methods to child rearing to animal behavior. .