What is extinction?

Ivan Pavlov, answered from the texts and cited to the page.

Ivan Pavlov answers

Extinction is what happens when a well-established conditioned reflex is repeatedly called forth without the unconditioned stimulus that originally built it.¹ The conditioned stimulus is applied again and again, at short intervals, and each time it goes unreinforced; the response weakens, and finally falls to nothing.² But mark this carefully: it is not destruction.

The reflex is suspended, not abolished — and the proof is that after a sufficient interval it returns spontaneously, without any fresh reinforcement.³ Fatigue cannot explain this, for a fatigued process does not restore itself in the absence of the stimulus that built it.⁴ What extinction reveals, then, is a positive nervous process — internal inhibition — not a mere lapse or wearing away.

The conditioned stimulus, which formerly called forth excitation in the cortical cells, now calls forth inhibition instead.⁵ This inhibition, furthermore, does not confine itself to the precise cortical point activated by the extinguished stimulus; it irradiates outward, so that neighboring points are drawn into the inhibitory after-effect as well.⁶

This is why I insist that the study of extinction demands a specially fitted laboratory: any extraneous stimulus of moderate strength falling on the animal during the experiment can dis-inhibit the reflex — freeing it momentarily from the inhibition — and so disrupt the entire course of observation.⁷

Sources

1. If a well elaborated and stable conditioned stimulus be repeatedly applied at short intervals, alone, without being followed by the unconditioned stimulus, then it begins to decrease and gradually becomes inactive.

   Lectures on Conditioned Reflexes

2. Stimulation by the metronome is not followed in this particular experiment by feeding, i.e. contrary to our usual routine the conditioned reflex is not reinforced. The stimulus of the metronome is repeated during periods of 30 seconds at intervals of two minutes.

   Conditioned Reflexes

3. This is not a complete destruction of the conditioned reflex, but only a temporary suspension. That this is so is proved by the spontaneous restoration of the reflex after an interval.

   Lectures on Conditioned Reflexes

4. That this extinction of the conditioned reflex is not a matter of fatigue is proved by its restoration without the assistance of the unconditioned stimulus.

   Lectures on Conditioned Reflexes

5. In the second type of inhibition, which may be termed internal inhibition, the positive conditioned stimulus itself becomes, under definite conditions, negative or inhibitory; it now evokes in the cells of the cortex a process of inhibition instead of the usual excitation.

   Conditioned Reflexes

6. the extinctive inhibition does not confine itself to the actual point in the cortex which was called into activity by the specific external stimulus, but irradiates over a wide area.

   Conditioned Reflexes

7. The study of the phenomena of internal inhibition, therefore, demands a specially fitted laboratory; if such does not exist, all accessory stimuli which are constantly falling upon the animal, chiefly sounds, frequently interrupt the course of our experiments.

   Lectures on Conditioned Reflexes