Each one of us has experienced forgetting and its consequences almost routinely. Why do we forget? Is it because the information we commit to our long-term memory is somehow lost? Is it because we did not memorise it well enough? Is it because we did not encode the information correctly or is it because during storage, it got distorted or misplaced? Many theories have been forwarded to explain forgetting and now you will read about those that seem plausible and have received considerable attention.
The first systematic attempt to understand the nature of forgetting was made by Hermann Ebbinghaus, who memorised lists of nonsense syllables and then measured the number of trials he took to relearn the same list at varying time intervals. He observed that the course of forgetting follows a certain pattern.
As the graph indicates, the rate of forgetting is maximum in the first nine hours, particularly during the first hour. After that the rate slows down and not much is forgotten even after many days. Although Ebbinghaus’s experiments constituted initial explorations and were not very sophisticated yet they have influenced memory research in many important ways. It is now upheld, almost unanimously, that there is always a sharp drop in memory and thereafter the decline is very gradual. Let us now examine the main theories, which have been advanced to explain forgetting.
Forgetting due to Trace Decay
Trace decay (also called disuse theory) is the earliest theory of forgetting. The assumption here is that memory leads to modification in the central nervous system, which is akin to physical changes in the brain called memory traces. When these memory traces are not used for a long time, they simply fade away and become unavailable. This theory has been proved inadequate on several grounds. If forgetting takes place because memory traces decay due to disuse, then people who go to sleep after memorising should forget more compared to those who remain awake, simply because there is no way in which memory traces can be put to use during sleep. Results, however, show just the opposite. Those who remain awake after memorizing show greater forgetting than those who sleep.
Because trace decay theory did not explain forgetting adequately, it was soon replaced by another theory of forgetting which suggested that new information that enters the long-term memory interferes with the recall of earlier memories and therefore, interference is the main cause of forgetting.
Forgetting due to Interference
If forgetting is not due to trace decay then why does it take place? A theory of forgetting that has perhaps been the most influential one is the interference theory which suggests that forgetting is due to interference between various informations that the memory store contains. This theory assumes that learning and memorising involve forming of associations between items and once acquired, these associations remain intact in the memory. People keep acquiring numerous such associations and each of these rests independently without any mutual conflict.
However, interference comes about at a time of retrieval when these various sets of associations compete with each other for retrieval. This interference process will become clearer with a simple exercise. Request your friend to learn two separate lists of nonsense syllables (list A and list B) one after the other and after a while ask her/him to recall the nonsense syllables of list A. If while trying to recall the items of list A, s/he recalls some of the items of list B, it is because of the association formed while learning list B are interfering with the earlier association which were formed while learning list A.
There are atleast two kinds of interferences that may result in forgetting. Interference can be proactive (forward moving) which means what you have learnt earlier interferes with the recall of your subsequent learning or retroactive (backward moving) which refers to difficulty in recalling what you have learnt earlier because of learning a new material. In other words, in proactive interference, past learning interferes with the recall of later learning while in retroactive interference the later learning interferes with the recall of past learning. For example, if you know English and you find it difficult to learn French, it is because of proactive interference and if, on the other hand, you cannot recall English equivalents of French words that you are currently memorising, then it is an example of retroactive interference.
Forgetting due to Retrieval Failure
Forgetting can occur not only because the memory traces have decayed over time (as suggested by the disuse theory) or because independent sets of stored associations compete at the time of recall (as suggested by the interference theory) but also because at the time of recall, either the retrieval cues are absent or they are inappropriate.
Retrieval cues are aids which help us in recovering information stored in the memory. This view was advanced by Tulving and his associates who carried out several experiments to show that contents of memory may become inaccessible either due to absence or inappropriateness of retrieval cues that are available/employed at the time of recall.
Let us understand this with the help of an example. Suppose you have memorised a list of meaningful words like hut, wasp, cottage, gold, bronze, ant, etc. in which words belonged to six categories (like places of living, names of insects, types of metal, etc.). If after a while you are asked to recall those you may recall a couple of them but if during the second recall attempt, you are also provided with category names, then you may find that your recall is near total. Category names in this example act as retrieval cues. Besides category names, the physical context in which you learn also provides effective retrieval cues.