Pavlov presented the dogs with a series of learning trials. On each trial a neutral stimulus - for example, a tone - was paired with a biologically important stimulus, food. Pavlov accompanied the pairing in a number of ways. An especially effective way was to have a lengthy waiting period between trials. The waiting period was called the intertrial interval (ITI). An effective ITI was two to three minutes. The learnign trial consisted of pairing the tone with food. The tone presentation was rather short - for example, 10 seconds. The food was presented at the end of the 10 second tone presentation. The tone was called the conditioned stimulus(CS) and the food was called the unconditioned stimulus (US).
On early trials the dog salivated when the food was presented. This salvation response to the food was called the unconditioned response(UR). Later, the dog salivated when the tone was presented. This salivation response to the tone was called the conditioned response (CR).
Definition of Terms
Pavlov chose the terms US, UR, CS, and CR carefully. The US and UR share the word unconditioned. This was a reminder that the animal does not need to be conditioned to respond to the stimulus in this way. That is, dogs naturally salivate to food. The CS and CR share the word conditioned. THis is a reminder that dogs do have to be conditioned to respond to the stimulus in this way. Dogs do not naturally salivate to a tone.