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

Classic conditioning

Let us recall that classical conditioning, also called Pavlovian conditioning, responsive conditioning, stimulus-response model or learning by association (E-E), is a type of associative learning that 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 it thanks to the associative connection of this stimulus with the stimulus that normally provokes this 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 (IS) .

In other words, the theory holds that the elicitation capacity is transferred from IE to CD, hence the emergence of the conditioned response (CR). The CD activates the same neural circuits that activated the IE.

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

How does it work?

The theory of stimulus substitution suggests that when two centres in the brain are activated, they are connected on the basis of experience .

But why does conditional response (CR) occur? Let’s see an example to understand it:

If, for example, you associate:

  • Light (EN) -> Food (EI) -> Salivation (RI)
  • Light (EC) -> Salivation (RC)

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

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

Limitations

However, the temporal contiguity between the CE and the IE does not always guarantee the acquisition of the conditional response (CR), as Pavlov argued. Sometimes CR occurs even when there is no strict temporal relationship between the stimuli; on other occasions, CR does not even 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 the theory of stimulus substitution, there are other theories that attempt to explain classical conditioning. The most important are three:

1. Theory of anticipation

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

2. Mackintosh theory

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

Rescorla and Wagner theory

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

In other words, the theory holds that the elicitation capacity is transferred from IE to CD, hence the emergence of the conditioned response (CR).
The CD activates the same neural circuits that activated the IE.

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

How does it work?

The theory of stimulus substitution suggests that when two centres in the brain are activated, they are connected on the basis of experience .

But why does conditional response (CR) occur?
Let’s see an example to understand it:

If, for example, you associate:

  • Light (EN) -> Food (EI) -> Salivation (RI)
  • Light (EC) -> Salivation (RC)

Light (EC) activates the “light” center of our brain.
As this centre is linked to the food centre (from previous experience gained through repeated EN -> EI presentations), the latter will also be activated.

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