Q.Why does forgetting take place?

Forgetting is a routine, universal experience, and psychologists have put forward several theories to explain why it happens — why information we appear to have committed to memory sometimes becomes unavailable when we need it. Three theories in particular have received serious research attention: trace decay, interference, and retrieval failure.

The earliest theory, trace decay (or disuse theory), assumes that learning produces physical changes in the nervous system called memory traces, and that these traces simply fade away when they are not used for a long time. This theory turned out to be inadequate: if forgetting really happened because unused traces decay with time, people who sleep after learning something should forget more than people who stay awake, since sleep offers no chance to 'use' the traces — but the opposite is actually found, with the waking condition producing more forgetting than the sleeping condition. Because of this and other problems, trace decay was largely replaced by interference theory.

Interference theory holds that forgetting happens because different sets of associations stored in memory compete with one another at the moment of retrieval, not because any association decays on its own. Interference can be proactive — earlier learning interfering with the recall of material learned later — or retroactive — later learning interfering with the recall of material learned earlier. This theory has been demonstrated experimentally using designs that compare an experimental group (which learns two lists) against a control group (which learns only one, resting instead of learning the second), and it remains one of the most influential explanations of everyday forgetting. …