1. in operant conditioning, the process in which a neutral stimulus acquires the ability to influence the future probability of a particular response by virtue of being paired with another stimulus that naturally enhances such probability. That is, the initially neutral stimulus or circumstance functions as effective reinforcement only after special experience or training. For example, a person teaching a dog to understand the command “sit” might provide a treat and a simultaneous popping noise from a clicker tool each time the dog successfully performs the behavior. Eventually, the clicker noise itself (the conditioned reinforcer or secondary) can be used alone to maintain the desired behavior, with no treat reward being necessary.

2. the contingent occurrence of such a stimulus or circumstance after a response. Also called conditioned reinforcement. Compare primary reinforcement.