One of the key differences between the concepts of STM and LTM is duration. “Duration” refers to how long a memory lasts before it is no longer available. Short term memories don’t last very long. An example of STM in action would be trying to remember a seven-digit phone number that you have just been given. This is maintained in the short-term memory by REPETITION until the number is dialled, and then fades once the conversation starts. The way most people keep information in their STM for more than a few seconds is to rehearse it.
So rehearsal is one way of keeping a memory active. The result of verbal rehearsal is that STM are held in the STM store and eventually become long term. Duration of LTM LTM refers to memories that last anywhere for 2 hours to 100 years plus, i. e. anything that isn’t short term. Some memories are very long lasting. For example Shepard (1967) tested duration of LTM.
He showed participants 612 memorable pictures, one at a time. An hour later they were shown some of these pictures among a set of others and showed almost perfect recognition. Four months later they were still able to recognise 50% of photographs.
The material to be remembered was more meaningful to the participants and therefore the duration of the LTM was better. Key study on duration of STM Lloyd and Margaret Peterson (1959) conducted a landmark study of the duration of STM. They enlisted the help of 24 students attending their university. The experimenter said a consonant syllable to the participant followed by a three-digit number (e. g. WRT 303 or SCX 591). The consonant syllable was selected to have no meaning. Immediately after hearing the syllable and number, the participants had to count backwards from this number in 3s or 4s until told to stop.
Then the participants were asked to recall the nonsense syllable. The reason for counting backwards was to stop the participants rehearsing the syllable because rehearsal would aid recall. Each participant was given two practice trials followed by eight trials. On each trial the retention interval (time spent counting backwards) was different. They found that participants remembered about 90% when there was only a 3-second interval and about 2% when there was an 18-second interval. This suggests that, when rehearsal is prevented, STM lasts about 20 seconds at most.
Evaluation The findings from the Peterson and Peterson study have been challenged. We might argue that, in this experiment, participants were relying on more than STM alone because they knew they were going to be asked to recall the items after an interval filled with a distracting activity. Other research such as Marsh et al, (1997) has suggested that when participants do not expect to be tested after this interval, forgetting may occur after just 2 seconds. This suggests that our understanding of the duration of STM may not be as clear-cut as first thought.
In fact, more recent research even suggests that the duration of STM is not as short as Peterson and Peterson’s study would suggest. Nairne’s et al (1999) found that items could be recalled after as long as 96 seconds. In Nairne’s study, participants were asked to recall the same items across trials, whereas in the earlier study different items were used on each trial, which would have led to interference between items, decreasing recall. Capacity and Encoding Capacity is a measure of how much can be held in memory. It is measured in terms of bits of information such as number of digits.
STM has a very limited capacity (less than 7 chunks of information) whereas LTM has potentially unlimited capacity. Increasing the capacity of STM The magic number 7+/-2 George Miller (1956) wrote a memorable article called “The magic number seven plus or minus two”. He reviewed psychological research and concluded that the span of immediate memory is 7; people can cope reasonably well with counting seven dots flashed onto a screen but not many more than this. Miller also found out that people can recall 5 words as well as they can recall 5 letters – we chunk things together and can then remember more.
The size of the chunk matters Simon (1974) found that people had a shorter memory span for larger chunks, such as 8-word phrases, than smaller chunks, such as one-syllable words. Evaluation Cowan (2001) reviewed a variety of studies on the capacity of STM and concluded that STM is likely to be limited to above 4 chunks. This suggests that STM may not be as extensive as was first thought. Vogel et al, (2001) looked at the capacity of STM for visual information and also found that 4 items was about the limit. Encoding in STM and LTM PAGE 23 Encoding is the way information is changed so that it can be stored in memory.
Information enters the brain via the senses. It is then stored in various forms such as visual codes (picture), acoustic forms (sounds), or a semantic form (the meaning of the experience). Information in the STM is mainly encoded acoustically (information is represented as sound); whereas information in LTM tends to be encoded semantically (information is represented by its meaning). Acoustic and semantic encoding We can compare the ways information is stored in STM and LTM in terms of encoding of the memory trace. Acoustic coding involved coding information in terms of the way it sounds
The multi-store model of memory The multi-store model of memory (MSM) is an explanation of how memory processes work. The MSM was first described by Richard Atkinson and Richard Shiffrin in 1968. There is three stores/components in the MSM which are the sensory memory, short-term memory and long-term memory. Sensory memory The sensory memory is composed of several stores which are the eyes, ears, nose, etc, and the corresponding areas of the brain. If a person’s attention is focused on one of the sensory stores, then the data is transferred to STM. Attention is the first step in remembering something.
Short-term memory Information held in STM is in a “fragile state”. It will disappear relatively quickly if rehearsal is prevented. Information will also disappear if new information enters STM pushing out the original information. This happens because STM has a limited capacity. Long-term memory The second step is moving information from STM to LTM. Atkinson and Shiffrin said that this also happens through rehearsal. The more something is rehearsed the more it will be remembered. This kind of rehearsal is referred to maintenance rehearsal. Evaluation The sensory store
Sperling (1920) gave participants a grid of digits and letters for 50 milliseconds. They were either asked to write down all 12 items or they were told they would hear a tone immediately after the exposure and they should just write down that row. When asked to report the whole thing their recall was poorer (5 items recalled, about 42%) then when asked to give one row only (3 items recalled, 75%). This show that information decays rapidly in the sensory store. The serial position effect Glazer and Cunitz (1966) gave participants a list of 20 words, presented one at a time, and then asked to recall words they could remember.
They tended to remember the words from the start of the list (primary effect) and from the end of the list (recency effect) but were less good at recalling words in the middle. The primary effects occur because the first words are best rehearsed and transferred to LTM. The recency effect occurs because these words are in the STM when people start recalling the list. Areas of the brain associated with STM and LTM One way to demonstrate the existence of separate stores in memory is to link STM and LTM to specific areas of the brain.
Modern techniques of scanning the brain can be used to take images of the active brain and enable us to see what region is active when a person is undertaking particular tasks. Research (Beardsley, 1977) has found that the prefrontal cortex is active when individuals are working on a task in STM. The working memory model Baddeley and Hitch (1974) used the term ‘working memory’ to refer to that bit of memory that you are using when you are working on a complex task which requires you to store information as you go along. The components of the working memory Central executive This is the key component of the working memory.
The function of the central executive is to direct attention to particular tasks, determining at any time how ‘resources’ are allocated to tasks. The central executive has a very limited capacity. Phonological loop This also has a limited capacity. The phonological loop deals with the auditory information and preserves the order of information. Baddeley (1986) further subdivided this loop into the phonological store and an articulatory process. The phonological store holds the words you hear, like an inner ear. The articulatory process is used for words that are heard or seen (inner voice). Visuo-spatial sketch pad
The Visuo-spatial sketch pad is used when you have to plan a spatial task (like getting from one room to another). Visual and/or spatial information is temporary stored here. Visual information is what things looks like and spatial information is the relationship between things. Logie (1995) suggested that the Visuo-spatial sketchpad can be divided into a visual cache (store) and inner scribe which deals with spatial relations. Episodic buffer Baddeley (2000) added the episodic buffer because he realised the model needed a general store. The episodic buffer is an extra storage system that has a limited capacity.
It integrates information from the central executive, the phonological loop and the Visuo-spatial sketchpad and also from the long-term memory. Evaluation Doing two tasks using the same or different components Hitch and Baddeley (1976) gave participants two tasks to do simultaneously. Task 1 occupied the central executive and task 2 either involved the articulatory loop or both the central executive and articulatory loop. Task 1 was slower when given a task involving both the central executive and articulatory loop. The speed on task 1 was the same whether using the articulatory loop or no extra task.
This shows that doing two tasks that involve the same component causes difficulty. Evidence for the central executive Bunge et al. (2000) used an fmri to see which parts of the brain were most active when participants were doing two tasks (reading a sentence and recalling the final word in each sentence). The same brain areas were active in either dual- or single – task conditions but there was significantly more activation in the dual-task condition indicating that increased demands were reflected in brain activity. Evidence for the Visuo-spatial sketchpad Baddeley et al. (1975b) demonstrated the existence of thee Visuo-spatial sketch pad.
Participants were given a visual tracking task (they had to track a moving light with a pointer). At the same time they were given kne of two other tasks: task 1 was to describe all the angles on the letter F, task 2 was to perform a verbal task. Task 1 was very difficult but not task 2. This is also evidence related to the effects of doing two tasks using the same or different components. Evidence for the episodic buffer Baddeley et al. (1987) found that, when participants were shown words and then asked for immediate recall, their performance was much better for sentences (related words) then for unrelated words.
This supports the idea of an immediate memory store for itesms that are neither visual nor phonological. Accuracy of Eye Witness testimony Loftus and Palmer were interested in whether misleading interesting distorted the accuracy of an eyewitness’s immediate recall. What did they do? 45 students were shown seven films of different traffic accidents. After each film the participants were given a questionnaire which asked them to describe the accident and then answer a series of specific questions about it. There was one critical question. This question was about ‘how fast were the cars going when they hit each other?
One group of participants were given this question whereas the other five groups were given the verbs smashed, collided, bumped or contacted in place of the word hit. What did they find? The group given the world ‘smashed’ estimated a higher speed that the other groups (about 41 mph). The group given the word ‘contacted’ estimated the lower speed (about 30 mph). Evaluation Supporting DO LATER (PAGE 33) Factors influencing the accuracy of eye witnessing testimony Many researchers have looked at the relationship between anxiety and accuracy in eyewitness testimony. Deffenbacher et al. 2004) carried out a meta-analysis of 18 studies published between 1974 and 1997, looking at the effects of heightening anxiety on accuracy of eyewitness recall. From these studies it was clear that there was considerable support for the hypothesis that high levels of stress negativity impacted on the accuracy of eyewitness memory. Anxiety enhances recall Christianson and Hubienette (1993) found when they questioned 58 real witnesses to bank robberies. Those witnesses who were threatened in some way were more accurate in their recall and remembered more detail than those who had been onlookers.
This continued to be true even 15 months later. The weapon focus effect Johnson and Scott (1976) identified the weapon-focus effect. In their initial experiment, Loftus et al. used two conditions, one involving a weapon and one not. In both conditions participants heard a discussion in an adjoining room. In condition 1 a man emerged holding a pen and with grease on his hands. In conditions 2 the discussion was rather more heated and a man emerged holding a paperknife covered in blood. When asked to identify the man from 50 photos, participants in condition 1 were 49% more accurate, compared with 33% accuracy in condition 2.
This suggests that the weapon may have distracted attention from the person holding it and therefore explain why eyewitnesses sometimes have poor recall for certain details of violent crimes. Evaluation Explaining the apparent contradiction Deffenbacher suggests that this contradiction in research finding could best be explained with reference to the Yerkes-Dodson law, which states that performance improves with increase of arousal up to some optical point then declines with further increase. Many researchers believe that anxiety effects in eye-witness testimony are curvilinear.
This means that small to medium increases in arousal may increase the accuracy of memory, but high levels interfere with accuracy. Those studies which had found improved memory accuracy were most likely dealing with increased arousal within the first part of the Yerkes-Dodson curve, whereas studies which showed that accuracy decreases with increased arousal were most likely operating in the second part of the curve. MORE EVALUATION!! The cognition interview Fisher and Geiselman (1992) developed an interviewing technique, the cognitive interview.
The original cognitive interview technique could be characterised by four distinct components 1. Report everything (hypermnesia) 2. Mental reinstatement of context- the interviewer encourages the interviewee to mentally recreate the environment and contacts from the original incident. 3. Changing the order- the interviewer may try alternative ways through the timeline of the incident, for example by reversing the order in which events occurred. 4. Changing the perspective- the interviewee is asked to recall the incident from multiple perspectives
The first two components are based on the principle that if there is consistency between the actual incident and the recreated situation, there is an increased likeliness that witnesses will recall more detail therefore more accurate in their recall. The latter two components are based on the assumption that information that observed can be retrieved through a number of different routes into an individual’s memory. Evaluation Kohnken et al. , (1999) did a meta-analysis of 53 studies found, on average, an increase of 34% in the amount of correct information generated in the cognitive interview compared with standard interviewing techniques.
Milne and Bull (2002) examined the relative effectiveness of each of the four components of the cognitive interview. Undergraduate students and children were interviewed using one of the components of the cognitive interview and compared to a control condition (where they were instructed to simply ‘try again’). When participants were interviewed using a combination of the components ‘mental reinstatement’ and ‘report everything’ their recall was significantly higher than in all other conditions.
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