Studies of Ivan Pavlov

Even before coming to this article, you might have heard of Pavlov's dogs. The work of the Russian physiologist Ivan Pavlov is well known. Pavlov demonstrated that neutral aspects of the environment can attain the capacity to evoke responses through pairing with other stimuli and that bodily processes can be influenced by environmental cues.

In the early 1900s, Pavlov was interested in the way the body digests food. In his experiments, he routinely placed meat powder in a dog's mouth, causing the dog to salivate. By accident, Pavlov noticed that the meat powder was not the only thing that caused the dog to salivate. The dog salivated in response to a number of stimuli associated with the food, such as the sight of the food bowl, or the entrance of the person bearing the food, or even the sound of the door closing when the food was brought in. Pavlov recognized that the dog's association of the sights and sounds with the food was an important type of learning, which came to be called classical conditioning.

Pavlov wanted to know why the dog salivated in reaction to various sights and sounds before eating the meat powder, He observed that the dog's behavior included both learned and unlearned components. The unlearned part of classical conditioning is based on the fact that some stimuli automatically produce certain responses apart from any prior learning; in other words they are inborn (innate). Reflexes are such automatic stimulus-response connections. They include salivation in response to food, nausea in response to spoiled food, shivering in response to low temperature, coughing in response to throat congestion, pupil constriction in response to light, and withdrawal in response to pain.

An unconditioned stimulus is a stimulus that produces a response without prior learning; food was the unconditioned stimulus in Pavlov's experiments. An unconditioned response is an unlearned reaction that is automatically elicited by the unconditioned stimulus. Unconditioned responses are involuntary; they happen in response to a stimulus without conscious effort. In Pavlov's experiment, salivating in response to food was the unconditioned response. In an example where someone were to flush the toiled while you were in the shower, causing the water to become scorchingly hot, no learning or experience would be the cause of the shriek of pain. The cry of pain was unlearned and occurred automatically. The hot water was the unconditioned stimulus, and the panic was the unconditioned response.

In classical conditioning, a conditioned stimulus is a previously neutral stimulus that eventually elicits a conditioned response after being paired with the unconditioned stimulus. The conditioned response is the learned response to the conditioned stimulus that occurs after conditioned stimulus to unconditioned stimulus pairing. Sometimes conditioned responses are quite similar to unconditioned responses, but typically they are not as strong.

In studying a dog's response to various stimuli associated with meat powder, Pavlov rang a bell before giving meat powder to the dog. Until then, ringing the bell did not have any particular effect on the dog, except perhaps waking the dog from a nap. The bell was a neutral stimulus. However, the dog began to associate the sound of the bell with the food and salivated when it heard the bell. The bell had become a conditioned response (Learned) and salivation was now a conditioned response. In the case of the scalding shower, the sound of the toilet flushing was the conditioned stimulus and the panicking was the conditioned response after the scalding water (unconditioned stimulus) and the flushing sound (conditioned stimulus) were paired.

Researchers have shown that salivation can be used as a conditioned response not only in dogs and humans but also in, of all things, cockroaches (Watanabe & Mitzunami, 2007) These researchers paired the smell of peppermint (the conditioned stimulus, which was applied to the cockroaches' antennae) with sugary water (the unconditioned stimulus). Cockroaches naturally salivate (the unconditioned response) in response to sugary foods, and after repeated pairings between peppermint smell and sugary water, the cockroaches salivated in response to the smell of peppermint (the conditioned response). When they collected and measured the cockroach saliva, the researchers found that the cockroaches had slobbered over that smell for two minutes.


Whether it is human beings, dogs, or cockroaches, the first part of classical conditioning is called acquisition. Acquisition is the initial learning of the connection between the unconditioned response and conditioned stimulus when these two stimuli are paired (as with the smell of peppermint and the sugary water). During acquisition the conditioned stimulus is repeatedly presented followed by the unconditioned stimulus. Eventually, the conditioned stimulus will produce a response. Albeit, classical conditioning is a type of learning that occurs without awareness or effort, based on the presentation of two stimuli together. For this pairing to work, however, two important factors must be present: contiguity and contingency.

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