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Higher Order Conditioning
Once an association has been made through classical conditioning, the conditioned stimulus can be used to acquire new learned associations. Here, when a conditioned stimulus (such as a bell that now triggers salivation) is repeatedly paired with a neutral stimulus (NS) such as a flashing light, the dog will learn to salivate in response to the light—without food ever being present! These multiple layers of learning help us understand how humans form associations between many different stimuli.
Jack Russell terrier: Thinkstock; Bell: Thinkstock; Dog bowl: Thinkstock; Bulb: Shutterstock