Pavlov's stimulus substitution theory

There are different theories that try to explain the concepts of classical conditioning. In this article we will talk about the stimulus substitution theory, proposed by Ivan Pavlov.

This theory holds that after classical conditioning occurs, the effects produced by the conditioned stimulus (EC) in the nervous system are effects similar to those of the stimulus unconditioned (EI). We are going to see in detail what this theory consists of.

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Classical conditioning

Let us remember that classical conditioning, also called Pavlovian conditioning, respondent conditioning, stimulus-response model or learning by associations (E-E), is a type of associative learning which was first demonstrated by Ivan Pavlov.

It is a type of learning according to which an originally neutral stimulus (which does not elicit a response), gets to cause it thanks to the associative connection of this stimulus with the stimulus that normally causes said answer.

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Stimulus substitution theory: characteristics

The stimulus substitution theory was proposed by Ivan Pavlov, a Russian physiologist and psychologist. The theory states that after classical conditioning, the effects produced by the conditioned stimulus (CS) on the nervous system are effects similar to those of the unconditioned stimulus (IE).

In other words, the theory holds that the eliciting capacity of the US is transferred to the CS, hence the appearance of the conditioned response (CR). The EC activates the same neural circuits that the EI activated.

Thus, the theory of stimulus substitution is based on the close similarity that is often observed between CR and the unconditioned response (IR). As we have seen, the association between the conditioned stimulus (CS) and the unconditioned stimulus (US) would produce a transfer of the eliciting capacity from the IBO to the CB, so that this would provoke, at a conditioned level, the same reflex reaction as the IS (Jenkins and Moore, 1973).

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How does it work?

Stimulus substitution theory suggests that When two centers of the brain are activated, they are connected from the experience obtained.

But why does the conditioned response (CR) occur? Let's see an example to understand it:

If for example, it is associated:

Light (EN) -> Food (EI) -> Salivation (RI)
Light (EC) -> Salivation (CR)

Light (EC) activates the "light" center of our brain. As this center is linked to the food center (from previous experience gained through repeated EN -> EI presentations), the latter will also be activated. Thus, the light center attached to the food center, will activate the salivary gland and produce salivation (CR).

Thus, according to the theory of stimulus substitution, the conditioned stimulus (CS) becomes a substitute for the unconditioned stimulus (US), the animal behaving before the CS as if it were the own IS.

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Limitations

However, the temporal contiguity between the CS and the US does not always guarantee the acquisition of the conditioned response (CR), as defended by Pavlov. Sometimes it happens that CR occurs even when there is no strict temporal relationship between the stimuli; on other occasions, even CR does not occur despite the temporal contiguity between the stimuli.

In fact, experimental results carried out in relation to the theory of stimulus substitution, show that conditioning with a pharmacological IE sometimes causes a CR opposite to the IR. This is a criticism of this theory.

Other related theories

In addition to stimulus substitution theory, there are other theories that attempt to explain classical conditioning. The most important are three:

1. Anticipation theory

Proposed by Konorski, this author differentiated between preparatory responses and consummatory responses. The CR would act as an adaptive response that serves as preparation for the IS forecast.

2. Mackintosh theory

He maintains that preexposure to a stimulus hinders his subsequent CR conditioning. Mackintosh suggested that animals try to get information from the environment that allows them predict the occurrence of biologically relevant events (EI’s).

3. Rescorla and Wagner theory

The main idea of this theory is that of the competition between various stimuli to associate with IS. Furthermore, the authors introduce the concept of surprise or “unexpectedness” of IS. Thus, the unconditioned stimulus gives an associative force to the CS as a function of surprise.

Bibliographic references:

Pavlov, I. P. (1927). Conditioned Reflexes: An Investigation of the Physiological Activity of the Cerebral Cortex. Translated and Edited by G. V. Anrep. London: Oxford University Press. p. 142.
Todes, D. (1997). Pavlov Isis Physiological Factory. 88, 205-246.
Graña, J. and Carrobles, J.A. (1991). Classic conditioning in addiction. Psicothema, 3 (1), 87-96.
Jenkins, H. M. and Moore, B. R. (1973). The form of the autoshaped response with food or water reinforcers. Journal of the Experimental Analysis of Behavior, 20, 163-181.