The correct answer is unconditioned stimulus, unconditioned response
The unconditioned stimulus (IS) is one that unconditionally causes a natural and automatic response. For example, when you smell one of your favorite foods, you can immediately feel very hungry and salivate. In this example, the smell of the food is the unconditioned stimulus.
The unconditioned response is the naturally occurring response to the unconditioned stimulus. For example, if the smell of food is the unconditioned stimulus, the feeling of hunger in response to the smell of food is the unconditioned response.
