Forgetting can be a useful way in clearing out the un-wanted clutter from our memories. We do not need to remember things like what we wore last Thursday. Forgetting in Short-term Memory Displacement We must remember that according to Miller, the capacity of S. T. M is limited to about seven items (+ or – two. ) Material that is circulating in our S. T. M that has not been sufficiently processed by our L. T. M. can be pushed out or displaced by new incoming information. Waugh and Norman (1965) used a technique known as the serial probe technique to investigate this idea.
This involved presenting individuals with a series of digits followed by the repetition of one of these digits known as the probe digit. They found that recall was good if the probe came towards the end of the series but was poor if it came towards the beginning of the series. This is consistent with the notion of displacement as the digits at the end of the list would still be available in S. T. M whereas the digits at the beginning of the list would seem to have been displaced by the following digits. This may not be the only explanation however.
Shallice (1967) found that a faster rate of presentation of the digits had an effect on performance. The faster the rate of presentation, the better the recall was which suggests time may be an important factor in forgetting. It has become difficult to isolate the effect of displacement from decay . Decay According to the decay theory, information is lost with the passage of time rather than displacement of memory trace. It is thought that there is a structural change that occurs in the brain when a memory trace is laid down.
Hebb (1949) believed that excitation of nerve cells cause a memory trace to be laid down. At this stage, which corresponds with S. T. M, this trace is fragile and likely to be disrupted. If it is not strengthened through with repeat neural activity e. g. rehearsal (usually verbal) the trace can fade away over time. However if rehearsed a permanent structural change can take place and the trace is no longer susceptible to decay.
This means that according to Hebb trace decay can only account for forgetting in S.T. M. It is difficult to test decay theory without introducing confounding factors but a researcher known as Reitman (1974) devised one she thought would be as pure a measure as possible. She decided that participants should be given a task between learning and recall, which prevented rehearsal but did not allow for further learning. She showed participants lists of five words for 2 seconds and then for a further 15 seconds asked them to listen out for a faint tone over earphones.
She thought that this would require effort and attention but not allow for the chance of any new learning. Under these conditions recall of the five words declined by about 24% over the 15 second period which led her to conclude that the decline in performance was due to decay however it is impossible to say whether or not any new information was learned by the individuals. It is clear that S. T. M is a fragile store from which information can be quickly or easily lost.
The precise mechanism for forgetting is unclear but it seems likely that interference, displacement and decay all have a major role to play. Forgetting in Long Term Memory Cell assemblies that house our memories located in L. T. M can sometimes decay without occasional rehearsal. Motor skills that require a continuous series of movements like swimming or riding a bike are resistant to decay whereas memory for some soft spoken or briefly exposed, irrelevant material is more likely to get lost. ]
Decay We have already seen that memories transferred to the L. T. M are fairly long lasting and stable. However that does not stop us from failing to remember things. This has led some psychologists to argue that decay can occur in L. T. M in the form of disuse. The idea is that knowledge or skills that have not been used in a long time eventually fade away. However skills requiring motor skills do not seem to be forgotten even if not used in a long time. Fleischman and Parker (1962) found that people who trained to fly using a flight simulator lost none of their skills over a 9 – 24 month period.
However, McKenna and Glendon (1985) studied 215 shop and office workers who had volunteered to learn cardiac resuscitation. Measures of performance were taken over a three-month to three-year period. Performance dropped sharply on the measures after three months and declined to extremely low levels after 3 years. Baddeley (1999) suggests that flying a plane or riding a bike involves a continuous skill as each action provides a cue for the next action. Skills such as resuscitation are more complex and require accurate knowledge as well as motor skills.
According to Baddeley these need continually refreshing if they are to be maintained. There is further evidence to suggest that verbal memories are remarkably resistant to long-term decay. Bahrick and Phelps (1987) found that American college graduates showed rapid forgetting of Spanish vocabulary over the first three to four years but showed little decline after this for the following 30 to 50 years. All this shows that even when time plays an important role forgetting it cannot be the only factor.