External inhibition is the observed decrease of the response of a conditioned reaction when an external (distracting) stimulus that was not part of the original conditioned response set is introduced. This effect was first observed in Ivan Pavlov's classical conditioning studies where the dogs would salivate less (conditioned response) when presented with the sound of the tuning fork (conditioned stimulus) in the distracting context of a passing truck (external stimulus). External inhibition is important for its main principle in classical conditioning where a conditioned response may decrease in magnitude after the external stimulus is introduced. This is especially advantageous for when trying to disassociate conditioned stimulus and responses. A practical example is where students who become anxious (conditioned response) upon standing in front of the class to give a presentation (conditioned stimulus) may feel less anxiety if their friends were sitting in front of the student presenting (external stimulus). The positive association of speaking to friends may distract the student from associating speaking to the entire class with anxiety.
Extent of external inhibition
The extent of external inhibition depends on several factors, including: The intensity of the external stimulus – the stronger the external stimulus, the greater the inhibition of the conditioned response. The amount of time it takes to notice the external stimulus – the shorter the time it takes for the subject to perceive the external stimulus, the stronger the effect will be on disrupting the conditioned response. Strict control of the learning environment – the presence of a distracting stimulus will lead to greater external inhibition when learning has occurred under tightly controlled conditions than when learning conditions are more variable.
External inhibition in relation to disinhibition
This same external stimulus can also lead to an increased response of a conditioned reaction, called disinhibition, when introduced after experimental extinction (when the conditioned response process is independent of the conditioned stimulus). During extinction, the subject has been unconditioned as to not show the conditioned response when presented by the paired conditioned stimulus. An example of disinhibition is where a rat that was conditioned to walk from point A to point B at the sound of the buzzer and then unconditioned, and introduced with a different stimulus, such as a blinking light, will again exhibit the conditioned reaction of walking to point B. The observed response of walking to point B after a blinking light stimulus will be relatively greater compared to the rat’s movement during the unconditioned phase (when the rat was not presented with either the buzzer or blinking light).
Experimental studies
"External Inhibition and Disinhibition Produced by Duplicate Stimuli", Wenger (1936) Wenger's 1936 study examined if the same external stimulus can be used to demonstrate both external inhibition and disinhibition and the relationship of the external stimulus to the intensity of external inhibition and disinhibition. Wenger conditioned participants with electro-dermal response (raising the foot to avoid the shock) to a red light using repeating presentations of a red light paired with a shock to the right foot. After the participants were conditioned, the extra stimulus of a tactual vibration to the left hand was introduced before the red light was shown in the absence of a shock stimulus. Following the principles of external inhibition, Wenger hypothesized that the after-effect of the tactual vibration would inhibit the conditioned response to the red light and lead to smaller movements of the foot to the red light. Disinhibition was tested after experimental extinction, where the red light was presented multiple times without any shock reinforcement. Following the principles of disinhibition, Wenger hypothesized that the tactual vibration will induce a greater reaction to the light stimuli when compared to the reactions from the external inhibition test. Both of Wenger's hypotheses were confirmed; Wenger observed that both external inhibition and disinhibition could be produced by the same external stimulus (tactual vibration). In addition, higher intensity of the external stimulus produced greater magnitudes of external inhibition and disinhibition however the functional strengths of externally inhibited and disinhibited responses were not considered decisive.