To investigate the various phenomena of salivary conditioning, Pavlov used a simple and effective experimental procedure. The subject was a dog, surgically prepared so that careful measurements of salivary flow could be obtained. The dog was held in a stock and isolated in a soundproofed chamber. Through various mechanical devices, meat powder could either be placed directly on the dog’s tongue or put in a food dish set before it. The experimenter could present, as desired, any of several controlled stimuli, such as the sound of a metronome or the flashing of a light.
The starting point for Pavlov’s demonstration was the unconditioned reflex or unconditioned response (UR) of salivation. The unconditioned reflex is an innate, built-in reaction or response to a stimulus Whenever meat powder is placed on the tongue of a normal dog the response of salivation will occur. The nerve pathways that underlie this reflexive response are so to speak, prewired. The sound of a metronome, on the other hand, will not cause a normal dog to salivate. The sound will probably elicit some response from the dog-its ears may prick up, or it may turn to look at the source of the sound. We can be quite certain, however, that it will not salivate. Pavlov now proceeded to make the dog salivate in response to the sound of the metronome. The trick is very simple.
We merely sound the metronome and shortly after we present the dog with meat powder. This sequence-metronome sound followed by meat powder-is repeated for a number of trials. The dog, on the first couple of trials, salivates only when the meat powder (the unconditioned stimulus, or US) is presented. After a few trials, however, it begins to salivate when the metronome sound (the conditioned stimulus, or CS) is presented Salivation now occurs before the meat powder is presented The sound of the metronome watch before had no relation to salivation, now reliably elicits a salivary response. When salivation occurs to a previously neutral CS, such as the sound of the metronome we refer to it as a conditioned reflex, or a conditioned response (CR).
Pavlov’s basic experiment is a clear example of what has come to be known as the law of classical conditioning. Whenever a previously neutral stimulus (CS) is presented in close temporal continuity (close in time) with an unconditioned stimulus (US) a response like that made to the US will come to be made to the CS. This is, of course a law about learning
The experience of the regular sequence-metronome sound followed by food-has adaptively modified the dog’s behavior. The CR is not always identical to the unconditioned response (UR); but it does seem that the conditioned response anticipates, and thus helps the animal to prepare for, delivery of the US. There are other occasions when the CR, although obviously related to the UR, may be directly opposite in form.
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