Juan developed a conditioned taste aversion to ranch potato chips when he had the stomach flu last year. Now he gets nauseous just seeing a bag of ranch potato chips. The US is the and the UR is the .

The US (unconditioned stimulus) is the stomach flu and the UR (unconditioned response) is the vomiting.

Explanation:

When it comes to classical conditioning, unconditioned stimulus is one that triggers a response, a reaction, naturally, automatically. Unconditioned response is, of course, the natural reaction we show when presented with an unconditioned stimulus. It is an automatic, unlearned response, a reflex. The stomach flu Juan had was an unconditioned stimulus that triggered the natural body response of vomiting. Notice, on the other hand, how the bag of potato chips has become associated with the unconditioned stimulus and response. In that case, potato chips are a conditioned stimulus, one that originally was neutral.