Project Summary Understanding complex, comorbid conditions of intellectual developmental disorder (IDD) is an NICHD priority. Severe problem behavior (e.g., self-injurious behavior, aggression) of children with IDD is prevalent, potentially dangerous, and negatively impacts social integration and quality of life. Function-based differential- reinforcement-of-alternative-behavior interventions reduce such behavior effectively, but treatment relapse is common when a caregiver cannot deliver reinforcement for the alternative behavior. Such relapse is known as resurgence. Previously, we developed a quantitative theory of resurgence based on two well-established principles: (1) individuals allocate proportionally more responding to options that produce proportionally more reinforcement, and (2) the value of past reinforcement decays hyperbolically as time passes. The theory provides a quantitative account of behavior in dynamically changing reinforcement conditions, including when all reinforcement ceases (i.e., extinction)—the conditions giving rise to resurgence. In Period 1 of this project, we showed the quantitative accuracy of many of the theory’s predictions with laboratory animals and we have shown similar relations in resurgence of severe problem behavior of children with IDD in the clinic. However, the most important and promising finding from Period 1 was one the theory failed to predict. We found that exposure to a treatment (i.e., contingency discrimination training, CDT) involving alternating sessions in which alternative reinforcement was and then was not available during continued extinction of a target response substantially mitigated resurgence. To account for these effects, we have developed a refined version of the quantitative theory suggesting that individuals exposed to CDT rapidly learn to discriminate the continued unavailability of reinforcement for the target behavior, even when reinforcement is not available for the alternative response, thus serving to inoculating them against later resurgence. These findings and the refined quantitative theory from Period 1 suggest promising, innovative, and unexplored procedures for treating severe problem behavior that are likely to produce better resurgence mitigation than existing approaches, while also avoiding some downsides of the current methods to mitigate resurgence of problem behavior (i.e., arbitrary stimuli that caregivers may lose or use incorrectly). Period 2 of this project will focus on this highly innovative approach identified in Period 1 in two aims by conducting: (1) the first randomized controlled trial evaluating the resurgence-mitigating effects of CDT on severe problem behavior of children with IDD and (2) a series of experiments with laboratory animals testing the refined theory under a range of conditions predicted to improve the efficacy, efficiency, and practicality of CDT in future clinical applications. This project represents a close collaboration between b...