Concurrent 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, in a two-alternative forced choice task, a pigeon in a Skinner box is 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 be linked so that behavior on one key affects the likelihood of
reinforcement on the other.
It is not necessary for responses on the two schedules to be
physically distinct. In an alternate 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 can respond on a
second key to change between the schedules. In such a "Findley
concurrent" procedure, a stimulus (e.g., the color of the main key)
signals which schedule is 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. Matching law is a rule for instrumental behavior which states
that the relative rate of responding on a particular response
alternative equals the relative rate of reinforcement for that response
(rate of behavior = rate of reinforcement). Animals and humans have a
tendency to prefer choice in schedules
