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Memory: Research studies

Short-term memory, cognitive interview research and others - take a closer look at the different Research Studies around memory and write the best work you can.

Short-term memory research

The capacity of the STM has been investigated using the digit span technique. Participants are shown or read a number of random digits and are then required to immediately recall these in consecutive order. The number of digits usually begins at three and increases every time by one further digit. The point at which the participant can no longer recall the digits in the correct order is recorded and the trial is repeated again with another set of random digits. After a number of trials, the point at which the participant is correct 50% of the time is defined as their digit span. This is a very simple and effective way to measure the capacity of an individual’s STM and results generally find digit span to be 7+/- 2 items.

To test the duration of STM the techniques used by psychologists must prevent participants from rehearsing the information because otherwise this information can be transferred to LTM and thus is no longer a valid measure of STM. The technique used by Peterson and Peterson (1959) involved participants being presented with a consonant trigram (TGY, PUI) for a very brief period of time and then being asked to engage in a distraction task to prevent rehearsal (counting backwards in 3s from a given number). Participants when then asked to recall the original trigram after varying intervals of time, starting at 3 seconds, and then increasing by 3 second intervals, up to 18 seconds. They found that participants were able to recall the trigram fairly easily after a 3 second interval (80% accuracy) but as the intervals got progressively longer the participants found it much more difficult to correctly recall the information. By 18 seconds there was only 10% accuracy, suggesting the STM can only store information for a brief period of time and is only temporarily maintained in this store.

Encoding in STM was initially investigated by Conrad (1964) who demonstrated that participants found it very difficult to recall a string of acoustically similar sounding letters in order e.g. P,C,V compared to acoustically dissimilar sounding letters e.g. H, X, L. Participants errors often involved substituting similar soundings letters for each other, suggesting that the STM is likely to use acoustic coding. Further research was then conducted by Baddeley (1966) investigating the encoding in both STM and LTM (see next section).

Long-term memory research

Baddeley’s (1966) research aimed to explore whether encoding in STM and LTM were different. To test STM, participants heard five words from a one specific category and were asked to recall these in the correct order immediately after they had been presented. They repeated this procedure 4 times using different words but from the same category. The categories included; acoustically similar words (e.g. man, map), acoustically dissimilar words (e.g. cat, tie), semantically similar words (e.g. small, slight) and semantically dissimilar words (e.g. young, early). Baddeley found that participants recall was much poorer when the words sounded similar (55% accuracy) compared to when they sounded different (75% accuracy). However, when participants recall was not immediate and occurred after a 20 minute interval the results were very different. Recall was much poorer when the words shared a similar meaning (55%) compared to the words whose meanings were completely different (85%). This study provides evidence that the memory stores encode information differently, namely that the STM encodes information acoustically and the LTM encodes information semantically.

The duration of LTM was investigated by Bahrick et al. (1975). Using a creative method, he recruited 392 people from an American high school that had graduated over a 50-year period and divided them into two conditions; the recognition group and the recall group. The recognition group were shown individual photos of their fellow graduates from the high school yearbook and had to match the person in the photo with a name from a given list. The recall group were not given a list of names to choose from and simply had to name the person they saw in the photo. Unsurprisingly, the recognition group were more successful at accurately identifying people than the recall group due to the name cues they were given. In the recognition condition there was 90% accuracy 14 years after graduation and 60% accuracy after 47 years but in the recall condition this decreased significantly to less than 20% after 47 years. This study demonstrates to us that particular information i.e. names and faces can be remembered for a very long period of time but our memory for this information is much better if given prompts/cues as shown by the recognition condition.

Case studies

Case studies in memory research have enabled cognitive psychologists to investigate areas of great interest. This type of research provides a wealth of knowledge that is otherwise inaccessible. HM is probably one of the most extensively studied patients as he was left with a severe memory impairment post brain surgery. HM is unable to from new memories and cannot retain any new information that is presented to him, suggesting damage to his LTM. However, HM has a normal digit span, can communicate normally and can remember events prior to the surgery suggesting that parts of his memory remain intact. This case study provides support for the MSM as it demonstrates that STM and LTM are likely to be separate stores and one can be impaired but the other still function effectively.

The case of Clive Wearing also provides some support for the separate components of the MSM. After contracting a serious illness, Clive was left brain damaged and suffering from severe amnesia. Like HM, Clive can no longer lay down new memories and has no memory of life events prior to the memory disruption, suggesting impairment in LTM. However, Clive is an interesting case because he is still able to talk, read, write and play the piano which surely requires the help of LTM?

Eye-witness testimony research - Anxiety and Age

There has been a huge body of research conducted on EWT and the impact that certain factors have on the accuracy of witness reports. Anxiety at the time of the event, especially if the crime being witness is violent or a weapon is present, has been shown to influence the way memories are encoded and reduces the accuracy of witness memories. Loftus (1979) found that correctly identifying a man, from a possible 50 photos, was significantly worse when the man was involved in a hostile exchange and emerged carrying a blood stained knife compared to when the man was involved in a quiet discussion and emerged carrying a pen, 33% and 49% respectively. This phenomenon has been named the ‘weapon focus’ effect and occurs when people focus their attention on the weapon and fail to attend to any details of the person themselves, thus resulting in poor identification of the perpetrator at a later date.

The age of the witness has also been identified as a factor that impacts the accuracy of recall. Anastasi and Rhodes (2006) used participants from 3 different age groups that were labelled as young (18-25), middle aged (35-45) and older (55-78). These participants were shown 24 photographs which they were instructed to rate on attractiveness and were then given a ‘filler’ activity. Their memory for the original 24 photos was tested by presenting them with 48 photos and asking them to identify the 24 that they had originally seen. The findings revealed that young and middle aged participants were significantly more accurate than older participants at identification but that all age groups were better at correctly identifying people from their own age group, now referred to as 'own age bias'.

Eye-witness testimony research - Misleading information

Another factor that affects accuracy of EWT is the use of leading questions during interviews after the event. It appears that information provided after the event can disrupt the already existing memory and reconstruction of the memory occurs. Loftus and Palmer (1974) were able to demonstrate that even very slight changes in wording of questions could produce this effect. They showed participants a film of a car accident and asked them to estimate the speed the vehicle was travelling at when the crash occurred. The critical question was “how fast were the cars going when they _____________ each other?” the participants were split into 5 conditions and were asked this question with a specific verb included in the gap. The 5 verbs varied in intensity from contacted, hit, bumped, collided to smashed. Loftus and Palmer found that as the intensity of the word increased so did the average estimation of speed e.g. contacted 31 mph, smashed 41mph. In a second experiment, Loftus and Palmer followed up their experiment by asking participants a week later “did you see any broken glass?”. Those who were exposed to the verb smashed were consistently more likely to answer ‘yes’ to this question, despite the fact there had been no broken glass in the original film. This suggests that the word used initially in the questioning had influenced their memory of the event and they were now recounting a reconstruction of the car crash, where they assumed there must have been glass because the cars had “smashed” into each other.

Cognitive interview research

Gesielman et al. (1988) conducted research into the effectiveness of the cognitive interview in comparison to a traditional police interview technique. The participants were 89 college students who were shown a video of violent crimes and interviewed individually after a period of 48 hours. The recordings of the interviews were analysed for the number of correct items recalled by the participants but also the number of errors made (incorrect items and confabulated (made-up) items). Gesielman et al. found that the cognitive interview technique was, on average, more effective in helping people recall correct information about the crimes compared to the standard interview technique (41.5 items, 29.4 items respectively), although, the number of errors for both groups were very similar (7.3 item, 6.1 items). Similar results reflecting the effectiveness of the cognitive interview have also been found by Fisher et al. (1989). He demonstrated a 47% increase in information gained from witnesses, for detectives who had received training in the technique compared to their previous questioning technique.