In classical conditioning, a conditioned stimulus generates a learned response.
In Ivan Pavlov's research on classical conditioning with dogs, the first stage involved an unconditioned stimulus and an unconditioned response: presenting a dog with meat powder and having him salivate in response to the food. Placing food in the dog's mouth naturally produces a salivation response; this is instinctual, not learned.
At this stage, a neutral stimulus is also presented. It produces no natural response by itself but comes to be associated with the unconditioned stimulus over time and can eventually elicit the same response. In Pavlov's original research, the sound of a bell was the unconditioned stimulus. It was paired with the presentation of meat powder, which produced salivation. After the powder and the sound had co-occurred for a period of time, the dog began to salivate when the sound occurred, regardless of whether the meat powder was administered.
Although most research in classical conditioning has involved reflexive behaviors that are typically involuntary, other nonreflexive behaviors have also been classically conditioned. The effects of the conditioned stimulus can vary according to the intensity of the stimulus. If the unconditioned stimulus is more intense, the conditioned stimulus will have a greater effect. By contrast, if the conditioned stimulus is not consistently paired with the natural, unconditioned stimulus, the conditioned stimulus will have a diminished or inconsistent effect. In addition, if an animal has associated a particular conditioned stimulus with a certain unconditioned stimulus and a new conditioned stimulus is presented, the animal will typically not generalize, or develop a response to the new conditioned stimulus. Psychologists refer to this lack of a response to the new stimulus as blocking.
If the conditioned stimulus occurs without the unconditioned stimulus, extinction will eventually take place. The conditioned stimulus will no longer have an effect, and the desired behavioral response will cease. It is possible to re-train or reactivate the response, and the reflex can be conditioned more easily when the two are again paired. Sometimes, after extinction has occurred, the conditioned stimulus will produce the reflexive behavior without the unconditioned stimulus, a process called spontaneous recovery.
Psychologists have applied theories of classical conditioning to human behavior. For example, a hungry infant cries and being fed makes the baby feel contented and no longer hungry. In this example, the baby cries with hunger and the primary caregiver quickly responds with a bottle, satisfying hunger, which makes the baby feel satiated and happy. Over a brief period of time, the baby comes to associate the presence of the primary caregiver with a feeling of comfort and happiness, developing an attachment to the caregiver.
See also Conditioned response ; Conditioning ; Learning ; Operant conditioning ; Pavlov, Ivan.
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