Thursday, 10 April 2014

Memory Duration STM/LTM Revision

STM Duration

Peterson and Peterson (1959)
Aim: To see how long items could remain in STM without rehearsal.
Procedure: Participants were presented with a Consonant trigram. Participants were then asked to count backwards in threes from specified number i.e 451. This was to stop them rehearsing the trigram. After intervals of 3,6,9,12,15 or 18 seconds, participants were asked to stop counting and to repeat the trigram. This procedure was repeated several times using different trigrams on each presentation. 
Results: Participants were able to recall about 80% of trigrams after a three second interval but their recall became progressively worse as the time intervals lengthened until, after 18 seconds, they could recall fewer than 10% correctly.
Conclusions: P&P concluded that information disappears or decays very rapidly from STM when rehearsal is prevented.
Evaluation: Lab so highly controlled, uses repeated measures design so avoids individual differences.
-However, trigrams are artificial things to remember and may not reflect everyday life.
-It is possible that the loss of information was more to do with capacity limitations than duration. The subsequent counting task might have pushed out (displaced the trigram).
-It is also possible that trigrams presented on earlier trails caused confusion (proactive interference*) for the participants and so later trigrams are incorrectly recalled.

*Proactive Interference: where things that have already been learned make it harder to learn new things

Extra Studies: Bherer et al. (2002)
Aim: to see if age and education affected STM duration
Procedure: recruited 24 young adults (mean age 25.8) and 24 older adults (mean 67.2 years) and further divided each group by educational level i.e lower being fewer than 13 years of education and higher being 13 years or more. They adapted the PP technique using oral presentation and recall of trigrams at 10-second retention intervals. Repeated Measures were used, in which there was a control condition (no prevention of rehearsal) and two experimental conditions (prevention of rehearsal by requiring participants to carry out either a numerical task or meaningless verbal task, such as saying blah blah). 
Results: In healthy adults age had no effect on performance level but educational level did. The lower education level performed less well than the more educated group across all conditions. Although both education levels were affected by the interference tasks, their impact on the higher education level by group's performance was impaired more by the numerical verbal task.

Factors affecting duration in STM:
Rehearsal: we can extend the duration of STM by rehearsing information. For example, if we look up a phone number in a directory, we tend to repeat it over in our heads in order to hold it in our memory for long enough to dial it correctly 
Intention to recall: it seems to make a difference whether we are making a conscious effort to recall material or not. Sebrechts et al. (1989) tested serial recall sets of three familiar English nouns. In the condition where pps were not expected to be asked to have to remember the words, correct recall fell to 1% after only four seconds.
Amount of information to be recalled: Murdock (1961) adopted the Peterson and Peterson technique but used either a single, three letter word such as cat or a set of 3 unrelated words such as pen, and lid. Unrelated words produced the same serial position curve while letters that made a recognisable word, recall was remarkably resistant to decay. Even though rehearsal had been prevented, accurate recall level was about 90 % after 18 seconds. It seems that the important factor is the number of chunks rather than the number of individual letters. 

LTM Duration 
Long Term Memory can hold limitless of information anything from a minute to a lifetime. It is difficult to measure but there is one famous study by Bahrick (1975).
Aim: An attempt to explore the length of times memories can be retained.
Method: tested the memory of 392 graduates of an American High School for their former classmates. They used various memory tests including the recognition of classmates pictures, matching names to pictures and recalling names with no picture cue.
Results: Participants performed remarkably well up to about 34 years although performance was better on recognition tasks than on recall tasks. There was a dip in performance on all types of memory test after 47 years but it is difficult to decide whether this deficit is due to the passage of time or the ageing effects in the brains of older participants.

Factors affecting duration of LTM
Experimental techniques: people can remember things better if they are given cues rather than starting from scratch. As you can see from the Bahrick study, accuracy increased when measured by a recognition rather than a recall test. 
Depth of learning: people are more likely to remember things for longer if they have learned it very well in the first place . Bahrick and Hall (1991) tested long term memory for algebra and geometry. People who had only taken maths courses up to secondary school level showed steady decline in their recall accuracy over the years. However, students who had gone on to take a higher course in maths showed high levels of accurate recall as much as 55 years later.
Pattern of learning: Bahrick(1987) looked at people who had learned Spanish and found that vocabulary items learned over spaced sessions were retained for longer than vocabulary learned in intensive sessions.
Nature of Material to be Learned: Conway et al. (1991) tested Open University psychology students and found that certain subject topics were recalled more accurately over time. Statistics was an area that seemed to be particularly well retained possibly because it involves the acquisition of skills rather than facts. 

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