The second explanation that has been put forward for forgetting information in long term memory is commonly known as the interference theory. This idea was suggested in the 1950s, it refers to the tendency for one memory to ‘interfere with’ the accurate retrieval of another (similar) memory. There are two types of interference – proactive interference (PI), this is where past learning interferes with current attempts to learn something, and retroactive interference (RI), when current attempts to learn something interfere with past learning. Psychologists have found evidence of both these types of interference. A typical study of interference uses the paired associates technique and two word lists (Underwood, 1957). Learning one list interferes with learning the other list.
This theory too has its criticisms, the first being that interference does cause forgetting but only when a similar stimulus is paired with two different responses. Interference effects require special conditions, and these conditions are rare in everyday life and therefore interference explains only a limited range of forgetting.
A second criticism is the fact that it is possible to recover from interference. Evidence to support this fact was from Tulving and Pstoka, their experiment contained two types of recall – free recall and cued recall, and participants were expected to learn word lists and recall them in different circumstances. If the interference theory was correct then the more lists a participant had to learn, the worst their performance would become. This is what Tulving and Pstoka found. Those who were given only one or two lists remembered a higher percentage than those given more lists. This is evidence of RI. When participants were given cued recall the effects of interference disappeared. With cued recall participants remembered more than before – about 70% regardless of how many lists they were asked to learn. This shows that interference effects may mask what is actually stored in memory. The information is there and available but cannot always be retrieved. This is called cue dependent forgetting (this means forgetting happens at the retrieval failure).
To conclude, the two explanations of factors that influence forgetting in long term memory are both logical and it is difficult to distinguish which theory is more accurate, as both come with their strengths and weaknesses.
b) Forgetting occurs in short term memory as well as long term memory, there are many experiments and studies that could be used to talk about forgetting in short term memory, but the main and most well known research was that conducted by Peterson and Peterson in 1959. Although the study was into duration in short term memory, we can also use it as an explanation for forgetting.
Peterson and Peterson enlisted the help of twenty four students attending university (this is a very common method used to find willing participants for a psychological investigation). Participants were asked to listen attentively as the experimenter said a three letter nonsense trigram (a random code of letters) followed by a three digit number. The idea was that the participant should count backwards from the number in threes or fours until told to stop. The participant was then asked to recall the nonsense trigram (this is the DV). Each participant was given two practice trials followed by eight trials. On each concessive trial, the retention interval (ie. time spent counting backwards), was different (this is the IV). It varied from three to eighteen seconds, in intervals of three.
Peterson and Peterson obtained several findings from their work, enabling them to deduce a logical conclusion, and these findings could also aid an explanation into forgetting in our immediate (short term) memory. Participants remembered more words accurately when they only had a three second retention interval, this decreased as the retention interval increased, and participants recalled far fewer words when the interval was at its greatest (eighteen seconds). They remembered approximately 90% when there was a three second interval compared to the 2% when the interval was increased to eighteen seconds.
We can conclude from these findings that recall for information rapidly decreases as time goes on, if verbal rehearsal was prevented, and has almost disappeared within about eighteen seconds. Although, the critiscisms of the study would have to be taken into consideration (as with any study), generally this research allows us to assess forgetting in short term memory, and the duration for which information remains in our short term memory.
c) Sometimes when accidents or crimes occur, it is necessary to try to gain as many accounts of the event from as many different perspectives as possible. This is commonly known as eyewitness testimony. The general definition of eye witness testimony is the evidence provided by a person who witnessed a crime, with a view to identifying the perpetrator. The accuracy of eye witness recall may be affected during initial encoding, subsequent storage and eventual retrieval. This is why it is necessary to gain as many eye witness recalls as possible as so to put together a general, fairly accurate account of what did occur. Much research has been carried out investigating this aspect of memory and has, as a result, aided our knowledge concerning eye witness testimonies.
Several decades ago, prior to the Devlin Report in 1976, it was generally assumed that eye witness testimony was sufficiently accurate to be used as sole evidence. However as time progressed and some of the inaccuracies of eye witness testimony were discovered, our understanding and interpretation of it has increased greatly. Elizabeth Loftus has conducted many different investigations into this topic, and her work is considerably the most accurate and well known evidence surrounding eye witness testimony, and is a key individual in helping us understand more about this concept.
Loftus worked together with Palmer to look at some of the ways memory can be distorted. The general aim of their study was to investigate the accuracy of memory after witnessing a car accident, and in particular to see if leading questions affected the accuracy of an eye witness’s immediate recall. Forty five students were shown seven films of different traffic accidents. After each film, the participants were given a questionnaire, asking them to describe the accident, and then to answer a series of specific questions about it. One critical question was included in the questionnaire: ‘About how fast were the cars going when they hit each other?’ One group of participants was given this question; the other four were given the same question, but with the verbs: ‘smashed’, ‘collided’, ‘bumped’ or ‘contacted’ in place of the word ‘hit’. The word given was the IV and the speed estimate given by the participant was the DV.
The mean speed estimate was calculated for each group, a range of different speeds were estimated. The group given the word ‘smashed’ estimated a higher speed than the other groups (approximately 41 m.p.h.). Whereas the group given the word ‘contacted’ estimated the lowest speed (approximately 32 m.p.h.). These findings lead us to conclude that the form of question can have a significant effect on a witness’s answer. This indicates that leading questions can affect the accuracy of memory. Such leading questions are an example of post event information (information given after the event which may alter memory). It is possible that such post event information to be altered before it is stored, and as a result, memory is permanently altered. A second explanation may be that the form of question actually alters the participants memory representation of the incident, which leads them to estimate a higher or lower speed.
Although this study was fairly comprehensive and seemed to provide logical conclusions, like any other psychological study, it has its criticisms. The first major criticism is that it was a laboratory experiment; this means that the conditions were not very much like they would be in real life. The study may not represent real life because people do not take the experiment seriously and are not as emotionally aroused as they would be if they were watching a real life car accident or robbery etc, or if they knew that their evidence would influence a trial. Emotional arousal may actually enhance the accuracy of memory, this was found by Christianson and Hubinette (1993). Therefore this experiment lacks ecological validity.
Furthermore, in many experiments, the experimental design leads to certain inevitable responses from participants. They may be unsure about how to behave and what to do – this may lead them to look for cues about what is expected of them. This means that they would be particularly receptive to certain features of the experiment, for example, leading questions. These features almost demand a response and this means that they lead to demand characteristics which might explain the finding of Loftus and Palmer’s study.
Later, Loftus and Palmer again teamed up to conduct a second experiment to assess whether or not memory was altered by post event information. A new set of participants were divided into three groups and again shown a film of a car accident. The control groups method was used, group 1 were given the word ‘smashed’, group 2 the verb ‘hit’ and group 3 (the control group) were not asked about the speed of the car at all. By having a control group, Loftus and Palmer could compare the experimental groups (those who did receive the IV – i.e. the verb used) with the control group, to see if the IV did have an effect.
The participants were asked ten critical questions about the accident a week later, including another critical question: ‘Did you see any broken glass?’ There was no broken glass in the film but, presumably, those that thought the car was travelling faster might expect that there would be broken glass. Participants gave higher speed estimate in the ‘smashed’ condition, as before. They were also more likely to think that they saw broken glass. This shows a significant effect of post-event information on later recall. However, some of the criticisms from the previous experiment must again be take into consideration for this follow up experiment.
Aside with working with Palmer, Elizabeth Loftus also made many more contribution to the psychological analysis of eye witness testimonies. In 1975, she carried out a study for which she showed participants a short video of eight demonstrators disrupting a lecture. Again, participants were later given a questionnaire including a critical question: ‘Was the leader of the four (or twelve) demonstrators a male?’ A week later the participants were asked several questions, including one about the number of demonstrators. Those who had four demonstrators gave a mean answer of 6.4, whereas those asked about the twelve demonstrators gave a mean of 8.9. This further supports the idea that post-event information effects subsequent recall.
During that same year Loftus also worked alongside Zanni, they used a film of a car accident, and then asked a series of questions including the critical question: ‘Did you see a broken headlight?’ Other participants were asked if they saw ‘the’ broken headlight. There was in reality, no broken headlight. As expected, participants were more likely to answer ‘yes’ if they had the question with ‘the’. This evokes the fact that leading questions affect recall.
Loftus et al. (1978) showed participants slides of events leading up to a car accident. One group was shown a car stopping at a junction with a ‘stop’ sign. The other group was shown the same but with a give way sign. Later all participants were given the same series of questions, half of each group were asked: ‘Did another car pass the car while it was at the give way sign?’, and the other half had the same question but with ‘stop’ sign. Finally, they were shown pairs of slides and had to identify which slides were in the original sequence. 75% of participants that had consistent questions picked the correct slide, whereas only 41% who had a misleading question picked the correct slide. This further illustrates that the misleading question affected their recall.
Loftus also conducted a number of smaller studies, in 1979 she not only identified the weapons focus theory, the fact that in real life situations weapons may distract attention from the perpetrator of the crime, and that this may be the explanation as to why eyewitnesses sometimes have poor recall for certain details of a crime. Another study by Loftus in 1979, showed that we may have very good recall for important information, and that recall of such information may not be distorted – even by misleading questions.
Clearly, from not only the quantity of research that Elizabeth Loftus has contributed to the understanding of eye witness testimony, but also from the quality of it and the conclusions that can be deduced from her work that she has made a large, and perhaps the most significant contribution to the way we view and value the reliability of eye witness testimonies. The findings from all of her studies allow us to assess all aspects of eye witness testimony, much more than ever before. It is likely that in the future even more research will be carried to out to discover yet more factors concerning eye witness testimony and it’s volubility and reliability, but it is undisputable that Loftus’ work has laid the basis for any new conclusions that are made, and will remain some of the most significant research on this factor of psychology.
Psychology. St Edwards School Sixth Form.