The unconditioned response was also salivation, but elicited not by the sound of the bell, but by the food.
In classical conditioning, an unconditioned response (which is an immediate response by a neutral stimulus), can become a conditioned response when associated with a conditioned stimulus.
In other words, it is only natural for a dog to salivate at the sight or smell of food (thus unconditioned) but the same respone becomes <u>conditioned</u> when associated with a different stimulus, such as the sound of a bell.
