Concurrent reinforcement schedules

In operant conditioning, concurrent schedules of reinforcement are schedules of reinforcement that are simultaneously available to an animal subject or human participant, so that the subject or participant can respond on either schedule. For example, a pigeon in a Skinner box might be faced with two pecking keys; pecking responses can be made on either, and food reinforcement might follow a peck on either. The schedules of reinforcement arranged for pecks on the two keys can be different. They may be independent, or they may have some links between them so that behaviour on one key affects the likelihood of reinforcement on the other.

It is not necessary for the responses on the two schedules to be physically distinct: in an alternative way of arranging concurrent schedules, introduced by Findley in 1958, both schedules are arranged on a single key or other response device, and the subject or participant can respond on a second key in order to change over between the schedules. In such a "Findley concurrent" procedure, a stimulus (e.g. the colour of the main key) is used to signal which schedule is currently in effect.

Concurrent schedules often induce rapid alternation between the keys. To prevent this, a "changeover delay" is commonly introduced: each schedule is inactivated for a brief period after the subject switches to it.

When both the concurrent schedules are variable intervals, a quantitative relationship known as the matching law is found between relative response rates in the two schedules and the relative reinforcement rates they deliver; this was first observed by R. J. Herrnstein in 1961.