What observations led Pavlov to conclude that extinction is caused by inhibition?
Pavlov agreed with Sechenov notions and believed that all the activities related to the CNS (central nervous system) can be characterized as either excitation or inhibition. He agreed to the theory that behavior is reflexive in nature, which is in turn a result of antecedent stimulation.
If inhibition does not interfere and modifies, both the unconditioned and conditioned stimuli result in the elicitation of unconditioned and conditioned reflexes. Though, with the passage of time and gaining of experiences, organisms learn the way to inhibit reflexive behavior.
The important point to note is that everyone experiences variety of stimuli, to which a response is elicited, and also results in inhibiting behavior. These two processes are fundamental and are seen every time.
Next, what Pavlov did was define the pattern of excitation and inhibition in terms of cortical mosaic. On presentation of a conditional stimulus to an organism, the elicited conditioned response will gradually vanish and this point is known as extinction.