The nature of memory

Short term memory, long term memory and duration

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Duration of memory

Memory refers to the process by which we retain information about events that have happened in the past.

Duration of short term memory - A few seconds

 Example; Trying to remember a 7 digit phone number that you have just been given. It is maintained in short term memory by repitition until the number is dialled, and fades away once the conversation starts.

The way most people keep information in their short term memory is by rehearsal - saying something over and over to yourself and therefore re-presents itself to short term memory and keeps the memory active.  If you carry on verbally rehearsing something it will eventually become a long term memory.

Duration of long term memory - 2 hours to 100 years

Example; Shepard tested the duration of long term memory. He showed participants 612 memorable pictures, one at a time. An hour later they were shown the same pictures amongst a set of others and showed almost perfect recognition. Four months later they were still able to recognise 50% of the photographs.

Studies of short term memory: Peterson and Peterson enlisted 24 students and recall was tested as follows: The experimenter said a nonsense trigram  followed by a 3 digit number (SCX 591) Immediatly after hearing the trigram the participants had to count backwards from the last number they heard in 3's or 4's until told to stop. Then the participant was asked to recall the trigram - the reason for counting backwards was to stop the participant rehearsing the trigram, as rehearsal aids recall. On each trial the retention interval (time spent counting backwards) was different - 3,6,9,12,15 or 18 seconds. Participants rememberd about 90% when there was a 3 second interval and about 2% when there was an 18 second interval. This study suggests that when rehearsal is prevented short term memory lasts about 20 seconds at most.

Validity - Criticism - only studying one type of memory (semantic)

Second criticism - not testing duration/when the participants were counting backwards the nonsense trigram could well have been displaced in short term memory by the numbers thus wiping out the syllables.

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