Early behaviorism posited that a stimulus would prompt a response in a simple cause-and-effect manner; Skinner later argued that the stimulus directly following a behavior (the antecedent) is just as important, if not more important, than the stimulus that came before it. Using Skinner’s principles, ABA was first coined in the 1950s, with a 1959 journal article becoming the first official study on its effectiveness. Early ABA studies focused predominantly on reducing self-injurious behaviors in patients with schizophrenia and neurodevelopmental disorders by providing positive and/or negative reinforcement* after the patient behaves in a way that the researcher wants to encourage.

*Reinforcement refers to a stimulus that encourages a behavior. Negative reinforcement differs from positive or negative punishment in that it is supposed to encourage the behavior by taking away a dislikable stimulus.