Final answer:
Extinction is the process by which a learned response diminishes when the conditioned and unconditioned stimuli are not paired together, leading to a decrease in the conditioned response.
Step-by-step explanation:
The weakening of a learned response after the conditioned and unconditioned stimuli no longer are presented together is called extinction. This occurs when, for example, a dog that has been conditioned to salivate at the sound of a tone because it predicts food no longer salivates when the tone is heard without the subsequent presentation of food. Extinction represents a decrease in the conditioned response when the conditioned stimulus is presented without the unconditioned stimulus.