Conditioning is a way of learning by association-that is, by putting together different ideas. In 1900, Ivan Pavlov, a Russian biologist, studied conditioning in dogs. Dogs innately salivate when they smell food. Pavlov rang a bell every time he gave food to a dog. Soon the dog started to associate the sound of the bell with the smell of food. After some time, it salivated when it heard a bell alone, without food.