Abstract
The overjustification effect suggests that external rewards may decrease intrinsically reinforced behaviors; however, this conclusion is often drawn from pre‐ and post‐assessment data. The majority of studies published in this area do not take repeated measures of behavior. In addition, previous research has not distinguished between the use of rewards and reinforcers by demonstrating a reinforcement effect; hence, it is possible that the occurrence of the overjustification effect varies depending on the nature of the stimuli that are used. This study extended previous research by evaluating whether the overjustification effect was relevant to the use of non‐reinforcing stimuli, reinforcers, or both. The effects of verbal praise were also evaluated in relation to the overjustification effect. Results indicated that behavior did not decrease below baseline levels following the contingent delivery of non‐reinforcing stimuli, reinforcers, or verbal praise. Copyright © 2009 John Wiley & Sons, Ltd.