<P> The sole criterion that determines if a stimulus is reinforcing is the change in probability of a behavior after administration of that potential reinforcer . Other theories may focus on additional factors such as whether the person expected a behavior to produce a given outcome, but in the behavioral theory, reinforcement is defined by an increased probability of a response . </P> <P> The study of reinforcement has produced an enormous body of reproducible experimental results . Reinforcement is the central concept and procedure in special education, applied behavior analysis, and the experimental analysis of behavior and is a core concept in some medical and psychopharmacology models, particularly addiction, dependence, and compulsion . </P> <P> Laboratory research on reinforcement is usually dated from the work of Edward Thorndike, known for his experiments with cats escaping from puzzle boxes . A number of others continued this research, notably B.F. Skinner, who published his seminal work on the topic in The Behavior of Organisms, in 1938, and elaborated this research in many subsequent publications . Notably Skinner argued that positive reinforcement is superior to punishment in shaping behavior . Though punishment may seem just the opposite of reinforcement, Skinner claimed that they differ immensely, saying that positive reinforcement results in lasting behavioral modification (long - term) whereas punishment changes behavior only temporarily (short - term) and has many detrimental side - effects . A great many researchers subsequently expanded our understanding of reinforcement and challenged some of Skinner's conclusions . For example, Azrin and Holz defined punishment as a "consequence of behavior that reduces the future probability of that behavior," and some studies have shown that positive reinforcement and punishment are equally effective in modifying behavior . Research on the effects of positive reinforcement, negative reinforcement and punishment continue today as those concepts are fundamental to learning theory and apply to many practical applications of that theory . </P> <P> The term operant conditioning was introduced by B.F. Skinner to indicate that in his experimental paradigm the organism is free to operate on the environment . In this paradigm the experimenter cannot trigger the desirable response; the experimenter waits for the response to occur (to be emitted by the organism) and then a potential reinforcer is delivered . In the classical conditioning paradigm the experimenter triggers (elicits) the desirable response by presenting a reflex eliciting stimulus, the Unconditional Stimulus (UCS), which he pairs (precedes) with a neutral stimulus, the Conditional Stimulus (CS). </P>

Who claimed that behavior is affected by positive reinforcement