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Capacity of STM

Study of word-length effect on immediate span by Baddeldy et al

Aim: To see if people could remember short words rather than long words

Procedure: The reading speed of the participants was measured, participants were then presented with sets of five words on a screen. The words were taken from one of two sets: a set of one syllable words or a set of polysyllabic words. Particiapnts were asked to write down the five words in serial order immediately after the presentation, they recalled several lists of long and short words

Findings: Participants could recall more short words than long words. They were able to recall as many words as they were able to articulate in about 2 secs. There was a strong positive correlation between reading speed and memory span

Conclusion: Immediate memory span represents the number of items of whatever length that can be recalled in approximately 2 secs

Evaluation: It may be that short words are easier to remember than long words becasue they are more similar to us. Miller had not been able to account for the findings of research which showed immediate memory, this study does

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Encoding in STM - Baddeley et al (1966)

Aim: To explore the effects of acoustic and semantic encoding in STM

Procedure: P's were divided into four groups. Each group heard a list of five words drawn from one of the following catergories: Acoustically similar words (e.g man, mad, map), acoustically dissimilar words (e.g. pen, day, few), semantically similar words (great, nig, large), semantically dissimilar words (e.g. hot, old, late). Immediately after hearing the five words, they were asked to recall them in the correct order. The procedure was carried out four times

Findings: Acoustically similar words were much harder to recall in the correct order (only 55% accurate) than words with disimilar sounds (about 75% accurate). Similarity of meaning had only a very slight detrimental effect. The effects of sound similarity disappeared when he tested p's long term learning, this suggests that a major factor affecting encoding is whether the items are stored in LTM or STM

Conclusion: These findings support those of Conrad: STM relies more on the sound of words than on their meaning

Evaluation: Conclusion of the study may not reflect the complexity of encoding


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Miller's magic seven numbers

Miller claimed that this finding works for lists of digits, letters, words, or larger 'chunks' of information

Over a number of trials the sequence length at which the participant is correct 50% of the time is defined as the digit span. Most people have a digit span of 'seven, plus or minus two.' According to Miller chunking occurs when we combine individual letters or numbers into a larger meaningful unit

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Realiability: Consistancy

Reconstructive memory: We probably dont have total recall for events but fill in gaps of what we think happened. Reconstructions are a combination of real elements of memory with your knowledge of the world

Schema: An organised package of information which stores knowledge about the world, and is stored in the LTM. E.g. they tell you that if you were wearing shorts its likely it will be summer

Sterotypes: Schemas that summerise large amounts of data, usually about people. They also influence how we organise information and how accurately we can recall information. They can be a source of prejudice

Leading question: Question phrased in a way that it biases a respondants reply.

Misleading information usually takes form of a question or statement following an eyewitness experience which wrongly implies that something happened when it did not

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Factors affecting eyewitness testimony

Age and memory - as you get older, your memory fades




Demand characteristics

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The cognitive interview

Developed by Geiselman et al (1985) and is designed to be used by police investigators. This interview technique is based on four instructions:

To recreate the context of the original incident: this does not involve revisiting the scene of the crime, by trying to recall an image of the setting such as the weather, the lighting, distinctive smells, any people nearby, what were you feeling etc

To report every detail: you are required to report back any information about the evnt you can remember, even if it does not seem to have a bearing on the crime

To recall the event in different orders: You are encouraged to describe the event in reverse order, or to start with an aspect of the the scene which seems most memerable and work backwards or forward from that point

To change perspectives: You are asked to attempt to describe the incident from the petspective of other people who were present at the time

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Research on the cognitive interview

Geiselman and colleagues tested the effectiveness of cognitive interview schedule by comparing it with standard police interviewing techiniques. They showed police training videos of violent crimes to a group of 89 students. About 48 hours later, the students were interviewed individually by American law enforcement officers. The interviewers had either been trained in standard police interviewing techniques or the new cognitive interview technique. Each interview was taped and analysed for accuracy of recall. Results were recorded as:

The number of correct items recalled

The number of errors

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Research on the cognitive interview


Correct items: 41.5       Incorrect items: 7.3        Confabulated items: 0.7


Correct items: 29.4       Incorrect items: 6.1       Confabulated items: 0.4

As the table shows the students recalled considerably more items in the cognitive interview than the standard interview, although the error rates were very similar. This study could be critized for its artificiality as it had undergraduate students

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Loftus and Burns (1982)

Aim: To investigate the effect of stress and violence on recall of a witnessed crime

Method: Participants were shown a video of a stimulated armed robbery. In condition one a boy was shot in the face whilist robbers made their get away. In the control condition the video was the same except for the shooting. The amounts and accuracy of recall were compared

Results: Participants who saw the violent version had less accurate and less complete recall than the control group. This was the case for events up to 2 minutes before the shooting and immediately before the shooting

Conclusion: The violent version had increased arousal and therefore reduced the processing of the information into memory

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