If only weak responses are reinforced, it eventually responds only very weakly. The process is called differentiation . A response must first occur for other reasons before it is reinforced and becomes an operant. It may seem as if a very complex response would never occur to be reinforced, but complex responses can be shaped by reinforcing their component parts separately and putting them together in the final form of the operant. Operant reinforcement not only shapes the topography of behavior, it maintains it in strength long after an operant has been formed.
Schedules of reinforcement are important in maintaining behavior.
If a response has been reinforced for some time only once every five minutes, for example, the rat soon stops responding immediately after reinforcement but responds more and more rapidly as the time for the next reinforcement approaches. If a response is reinforced when a given number of responses has been emited, the rat responds more and more rapidly as the required number is approached. When reinforcement occurs after an average number of responses but unpredictably, the schedule is called variable-ratio . It is familiar in gambling devices and systems which arrange occasional but unpredictable payoffs. The required number of responses can easily be stretched, and in a gambling enterprise such as a casino the average ratio must be such that the gambler loses in the long run if the casino is to make a profit.