Classical conditioning is one of the two main forms of simple learning. The other is instrumental conditioning, which is also known as operant conditioning. When a dog responds (e.g., sitting) to the commands of its master to get some biscuits (reinforcement), the dog has learnt an instrumental response. As a consequence of its response, the dog is rewarded. In other words, dog’s response was instrumental in fetching a sought after reward.

On the face of it, there are many similarities between this form of learning and classical conditioning. Compare the example above with Pavlov’s dog that has learnt to salivate to bell. In both cases, we have a stimulus, which determines whether a response is to be made (the bell and the command of the master). In both cases, response occurs more frequently with training (salivation and sitting in response to the command of the master). Finally, in both cases, we have reinforcement, which maintains a response (meat powder and dog biscuits). Despite these similarities, there are also important differences.

In instrumental conditioning, reinforcement is given only when the response is made. But in classical conditioning, the UCS is presented irrespective of what the animal does. In classical conditioning, the UCS evokes or elicits a natural biological response, on which the organism has little control. But in instrumental learning, the animal emits a voluntary response, which is either strengthened or weakened depending on its positive or negative consequences. Furthermore, in Pavlovian conditioning, the organism learns the relation between two stimuli, the CS and the UCS. Pavlov has called it S-S learning.

In instrumental learning, the animal has to learn the connection between a stimulus and a response, which is an S-R type of learning. The organism performs deliberately to produce a desirable outcome. The term ‘operant’ emphasizes this point; the organism operates on its environment to produce some desirable result. Hence, instrumental conditioning is also known as operant conditioning. The similarities and differences between classical and operant conditioning would be discussed in greater detail later. We now turn to early research on the behavior of cats and rats.

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The experimental study of instrumental conditioning began a decade before Pavlov. While Pavlov was studying dogs in Russia, Edward L. Thorndike (1874-1949), an American psychologist was studying cats in puzzle boxes. His brilliant doctoral dissertation on Animal Intelligence gave American psychology the theory of trial-and error learning and the ‘Law of Effect’.

Thorndike put a hungry cat inside a puzzle box, and a piece of fish outside to escape from the box; the cat had to learn how to open the latch inside the box. At first the cat made a number of ineffective responses. Accidentally, while moving inside the box, the cat happened to pull the loop that opened the door, allowing the cat to come outside and eat the food. The cat was returned to the box. It then made random movements until it pulled the loop for the door to open. On subsequent trials, the cat made fewer and fewer random movements, and more and more correct responses leading to the goal. With increasing trials, errors reduced and the correct response was learned.

Thorndike developed the Law of Effect, which states that behaviors followed by positive outcomes are strengthened and behaviors followed by negative outcomes are weakened. It is called Law of Effect, because whether a response would be strengthened or weakened depends upon the effect such a response produces. Thorndike believed that law of effect operates naturally and automatically as leaves fall off a tree during autumn or as animals breathe to live. Through trial and experience, the animal makes a direct connection between the stimulus (total stimulus situation inside the puzzle box) and the response (motor reaction of pulling the loop). The organism learns an S-R connection.

Thorndike’s early research provided the foundation for the advanced work on instrumental conditioning by one of the century’s most influential psychologist, B.F. Skinner.