concurrent-chains procedure
a procedure in which completion of either of two concurrent schedules of reinforcement, called the initial links, results in presentation of another schedule of reinforcement, called a terminal link, rather than primary reinforcement itself. Completion of the terminal-link schedule results in primary reinforcement. The initial links are concurrently available, in effect giving the organism an opportunity to choose between two terminal links. Once a terminal link is earned, however, it must be completed before the next period of choosing is made available.