Useful Notes on the 2 Important Theories about Classical Conditioning
(i) Theory of stimulus substitution;
(ii) Information and expectation theories.
We would discuss these two in brief.
(i) Stimulus Substitution:
The theory, which originated with Pavlov and was influential for many years, relies on the idea that the CS, simply as a result of pairing with the US, acquires the capacity to substitute for the US in evoking a response. In other words, an association, a link or a bond is formed between the CS and the US so that the CS becomes the equivalent of the US in eliciting a response. Pavlov thought this linkup, or association, took place in the brain.
He thought that two areas of the brain, one for the CS and one for the US, became activated during the conditioning procedure and that activation of the US area resulted in a reflex, or automatic, response. As a result of the CS- US pairings during the conditioning procedure, he theorised, the CS acquired the ability to excite the US area, thus, leading to the response.
While the idea of stimulus substitution is appealingly simple, it is not currently accepted by most learning theorists. A major difficulty with the theory is that it says the conditioned response (CR) should be the same as, or at least very similar to, the unconditioned response (UR).
According to this theory, all that has happened is that the CS has acquired the ability to evoke the response after conditioning. The response has not changed; the change is in the stimulus that elicits it. However, it is clear that the CR may not be at all like the UR. For instance, when using mild foot shock as the US and a tone as the CS, the unconditioned response of rats to the shock is an increase in running and activity, but the conditioned response to the tone is a decrease in activity-a response known as ‘freezing”.
(ii) Information and Expectations:
Other theories of the conditioning process take the view point that the CS becomes a signal for the US. Thus, when the CS is presented, the US is expected, and the learner responds in accordance with this expectations.
How does the CS become a signal for the US? A number of experiments have led to the view that this happens because the US is a surprising, or novel, event. The surprising US induces the learner to look back through recent memory. The CS is the event consistently found in memory on each trial before the US. An association, or link, is thus, said to be formed between the memory trace of the CS and the US. Now when the CS occurs, the US is expected.
The conditioned response is made in anticipation of the US. The form of the conditioned responses associated with eating, such as running to the place where the food is kept if the dog is not confined, will occur. Thus, in this view, conditioned responses are not automatically stamped in by CS-US pairings. Rather, they are behaviours, or actions, engaged in by the learner in expectation of a future event the US.