Ivan Pavlov’s work is also important to the field of ABA. He worked in the late 1800s to early 1900s in the field of classical conditioning (FK-13-14). Classical conditioning is the process of pairing an unconditioned response with a conditioned response. In the case of Pavlov, he paired the unconditioned response of a bell sound with the conditioned response of salivation when food was presented to an animal. After a number of trials of the pairing, only the sound of the bell was needed to make the animal salivate since it had been paired with the conditioned response.