Skinnerian Conditioning

Skinnerian Conditioning
In addition to changing the strength of responses, operant conditioning
can be used to mold entirely new behaviors. This process is referred to as
shaping and was described by American psychologist B. F. Skinner (1904-
1990), who further developed the field of operant conditioning. Suppose
that the experiment’s objective was to train an animal, such as a laboratory
rat, to press a lever. The rat could be given a piece of food (Sr) each time it
pressed the lever (R), but it would probably be some considerable time before
it would do so on its own. Lever pressing does not come naturally to
rats. To speed up the process, the animal could be “shaped” by reinforcing
successive approximations of lever-pressing behavior. The rat could be given
a food pellet each time that it was in the vicinity of the lever. The Law of Effect
predicts that the rat would spend more and more of its time near the lever
as a consequence of reinforcement. Then the rat may be required to
make some physical contact with the lever, but not necessarily press it, in order
to be rewarded. The rat would make more and more contact with the lever
as a result. Finally, the rat would be required to make the full response,
pressing the lever, in order to get food. In many ways, shaping resembles the
childhood game of selecting some object in the room without saying what it
is, and guiding guessers by saying “warmer” as they approach the object, and as they move away from it, saying nothing at all. Before long, the guessers
will use the feedback to zero in on the selected object. In a similar manner,
feedback in the form of reinforcement allows the rat to “zero in” on the operant
response.
Skinner also examined situations where reinforcement was not given for
every individual response but was delivered according to various schedules
of reinforcement. For example, the rat may be required to press the lever a
total of five times (rather than once) in order to get the food pellet, or the
reinforcing stimulus may be delivered only when a response occurs after a
specified period of time. These scenarios correspond to ratio and interval
schedules. Interval and ratio schedules can be either fixed, meaning that
the exact same rule applies for the delivery of each individual reinforcement,
or variable, meaning that the rule changes from reinforcer to reinforcer.
For example, in a variable ratio-five schedule, a reward may be given
after the first five responses, then after seven responses, then after three. On
average, each five responses would be reinforced, but any particular reinforcement
may require more or fewer responses.
To understand how large an impact varying the schedule of reinforcement
can have on behavior, one might consider responding to a soda machine
versus responding to a slot machine. In both cases the operant response
is inserting money. However, the soda machine rewards (delivers a
can of soda) according to a fixed-ratio schedule of reinforcement. Without
reward, one will not persist very long in making the operant response to the
soda machine. The slot machine, on the other hand, provides rewards (delivers
a winning payout) on a variable-ratio schedule. It is not uncommon
for people to empty out their pockets in front of a slot machine without receiving
a single reinforcement.