Operant Conditioning and
Behaviorism - an historical outline
Around the turn of the century, Edward Thorndike attempted
to develop an objective experimental method for the mechanical problem
solving ability of cats and dogs. Thorndike devised a number of wooden crates
which required various combinations of latches, levers, strings and treadles
to open them. A dog or a cat would be put in one of these 'puzzle-boxes' and,
sooner or later would manage to escape from it. Thorndike's initial aim was
to show that the anecdotal achievements of cats and dogs could be replicated
in controlled, standardised circumstance, however,
he soon realised that he could now measure animal
intelligence using this equipment. His method was to set an animal the same
task repeatedly, each time measuring the time it took to solve it. Thorndike
could then compare these 'learning-curves' (see figure below) across
different situations and different species.
Thorndike was particularly interested in discovering whether his animals
could learn their tasks through imitation or observation. He compared the
learning curves of cats who had been given the opportunity of observing
others escaping from a box with those who had never seen the box being solved
and found no difference in their rate of learning. He obtained the same null
result with dogs and, even when he showed the animals the methods of opening
a box by placing their paws on the appropriate levers and so on, he found no
improvement. He fell back on a much simpler trial and error explanation of
learning. Occasionally, quite by chance, an animal performs an action which
frees it from the box. When the animal finds itself in the same position
again it is more likely to perform the same action again. The reward of being
freed from the box somehow strengthens an association between a stimulus,
being in a certain position in the box, and an appropriate action. Reward
acts to strengthen stimulus-response associations. The animal learns to solve
the puzzle-box not by reflecting on possible actions and really puzzling its
way out of it but by a quite mechanical development of actions originally
made by chance. By 1910 Thorndike had formalised
this notion into a 'law' of psychology - the law of effect. In full it reads:
"Of several responses made to the same situation those which are
accompanied or closely followed by satisfaction to the animal will, other
things being equal, be more firmly connected with the situation, so that,
when it recurs, they will be more likely to recur; those which are
accompanied or closely followed by discomfort to the animal will, other
things being equal, have their connections to the situation weakened, so
that, when it recurs, they will be less likely to occur. The greater the
satisfaction or discomfort, the greater the strengthening or weakening of the
bond." Thorndike maintained that, in combination with the law of
exercise, the notion that associations are strengthen by use and weakened
with disuse, and the concept of instinct, the law of effect could explain all
of human behavior in terms of the development of myriads of stimulus-response
associations. It is worth briefly comparing trial and error learning with classical
conditioning. In classical conditioning a neutral stimulus becomes
association with part of a reflex (either the The behaviorist position that human behavior could be explained entirely
in terms of reflexes, stimulus-response associations, and the effects of reinforcers upon them entirely excluding 'mental' terms
like desires, goals and so on was taken up by John Broadhus Watson in his 1914 book 'Behavior: An
Introduction to Comparative Psychology.'. Watson had also been involved in
the introduction of the most favoured subject in
comparative psychology - the laboratory rat. One of his early jobs which he
used to fund his Ph.D. was as a caretaker, one of whose duties was to look
after laboratory rats used in studies intended to mimic 'real-life' learning
tasks such as navigating complex mazes. Watson became adept at taming rats
and found he could train rats to open a puzzle-box like Thorndike's for a
small food-reward. He also studied maze-learning but simplified the task
dramatically. One type of maze is simply a long straight alley with food at
the end. Watson found that once the animal was well trained at running this
'maze' it did so almost automatically. Once started by the stimulus of the
maze its behavior becomes a series of associations between movements (or
their kinaesthetic consequences) rather than
stimuli in the outside world. This is made plain by shortening the alleyway -
the well-trained rats now run straight into the end wall. This was known as
the kerplunk experiment. The development of
well-controlled behavioral techniques by Watson also allowed him to explore
animals sensory abilities, for example their abilities to discriminate
between similar stimuli, experimentally. Watson's theoretical position was
even more extreme than Thorndike's - he would have no place for mentalistic concepts like pleasure or distress in his
explanations of behavior. He essentially rejected the law of effect, denying
that pleasure or discomfort caused stimulus-response associations to be
learned. For Watson, all that was important was the frequency of occurrence
of stimulus-response pairings. Reinforcers might
cause some responses to occur more often in the presence of particular
stimuli, but they did not act directly to cause their learning. Watson could
therefore reject the notion that some mental traces of stimuli and responses
needed to be retained in an animals mind until a reinforcer
caused an association between them to be strengthened, which is a rather mentalistic consequence of the law of effect. Publishing his second book 'Psychology from the Standpoint of a
Behaviorist' in 1919, Watson became the founder of the american
school of behaviorism. His rejection of mentalism
was total. He felt that thought was explicable as subvocalisation
and that speech was simply another behavior which might be learned by the
law-of effect. In 'Psychology from the Standpoint of a Behaviorist' he
addresses a number of practical human problems such as education, the
development of emotional reaction and the effects of factors like alcohol or
drugs on human performance. He even suggests that thought processes might be
investigated by monitoring movements in the larynx. Watson believed that
mental illness was the result of 'habit distortion' which might be caused by
fortuitous learning of inappropriate associations which then go on to
influence a person's behavior so that it become ever more abnormal. Watson
tested part of this hypothesis on a baby in the hospital in which he worked.
The baby, 'little Albert', apparently showed no particular fears or phobias
about anything apart from sudden loud sounds. For example, when Watson placed
a tame white rat in little Albert's lap the child happily played with the
animal. On a subsequent occasion Watson placed the rat in Albert's lap and
his assistant made a loud noise by striking a large steel bar directly behind
Albert's head. One week later Albert was subjected to the same experience.
After this, when Albert was showed the rat be began to fret, appearing
anxious. Similar reactions were produced by other furry objects (a fur coat).
Watson was keen to use this as evidence for the behavioral basis of phobias, however, apparently Albert's reactions to the rat
were quite mild. Nevertheless, one of the most widespread applications of
conditioning has been in the treatment of phobias and other behavior problems
and the case of Little Albert is often cited as the first experiment in this
field. In the 1920's behaviorism began to wane in popularity somewhat. A number
of studies in the
At the same time as this work was appearing in the In 1938 Burrhus Friederich Skinner
published what was arguably the most influential work on animal behavior of
the century 'The Behavior of Organisms'. In the interim it had been shown that
Tolman's results were sensitive to factors like the
openness of his maze - if the rats could not see stimuli outside the maze
they did not make appropriate choices when it was blocked, suggesting that
they may have learned many stimulus response associations in different parts
of the maze, perhaps in sequence, rather than having internalised
a map of it. Skinner resurrected the law of effect in more starkly behavioral
terms and provided a technology which allowed sequences of behavior produced
over a long time to be studied objectively. His Skinner-Box
was a great improvement on the individual learning trials of Watson and
Thorndike. Skinner developed the basic concept of operant
conditioning, claiming that this type of learning was not the result of
stimulus-response learning - for Skinner the basic association in operant
conditioning was between the operant response and the reinforcer,
the discriminative stimulus served to signal when this association would be
acted upon. This document was restructured
from a lecture kindly provided by R.W.Kentridge |
