Pavlov’s Theory Of Stimulus Substitution

Pavlov's theory of stimulus substitution

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

This theory maintains that after classical conditioning occurs, the effects produced by the conditioned stimulus (CS) in the nervous system are effects similar to those of the unconditioned stimulus (US). Let’s see in detail what this theory consists of.

Classical conditioning

Let us remember that classical conditioning, also called Pavlovian conditioning, responder conditioning, stimulus-response model or learning by associations (EE), 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 (that does not provoke a response) comes to provoke one thanks to the associative connection of this stimulus with the stimulus that normally provokes said response.

Stimulus substitution theory: characteristics

The theory of stimulus substitution 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 similar to those of the unconditioned stimulus (US).

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

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Thus, stimulus substitution theory 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 IS to the CS so that this would provoke, at a conditioned level, the same reflex reaction as the US (Jenkins and Moore, 1973).

How does it work?

Stimulus substitution theory suggests that When two centers of the brain are activated, they are connected based on 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 (EC) activates the “light” center of our brain. As this center is linked to the food center (from previous experience gained through repeated presentations of EN –> EI), the latter will also be activated. Thus, The light center joined to the food center will activate the salivary gland and produce salivation (RC).

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


However, the temporal contiguity between the CS and the US does not always guarantee the acquisition of the conditioned response (CR), as Pávlov defended. It sometimes 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.

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In fact, experimental results carried out in relation to the theory of stimulus substitution show that conditioning with a pharmacological US sometimes causes a CR opposite to the IR. This represents 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 anticipation of IS.

2. Mackintosh theory

He maintains that pre-exposure to a stimulus hinders subsequent CR conditioning. Mackintosh suggested that animals try to obtain information in the environment that allows them predict the occurrence of biologically relevant events (EI’s).

3. Theory of Rescorla and Wagner

The main idea of ​​this theory is that of competition between various stimuli to associate with IS. Furthermore, the authors introduce the concept of surprise or “unexpectability” of IS. Thus, the unconditioned stimulus gives an associative force to the CS depending on its surprise.

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