Study notes

​Duration of Short-term Memory

  • Levels: AS, A Level
  • Exam boards: AQA, Edexcel, OCR, IB

Peterson & Peterson (1959) investigated the duration of short-term memory by conducting a laboratory experiment with a sample of 24 psychology students.

The students had to recall meaningless three-letter trigrams (for example, THG, XWV) at different intervals (3, 6, 9, 12, 15 or 18 seconds). To prevent rehearsal (practice) the students had to count backwards in threes or fours from a specific number, until they were asked to recall the letters.

Peterson & Peterson found that the longer the interval the less accurate the recall. At 3 seconds, around 80% of the trigrams were correctly recalled, whereas at 18 seconds only 10% were correctly recalled.

Peterson & Peterson concluded that short-term memoryhas a limited duration of approximately 18 seconds. Furthermore, the results show that if we are unable to rehearse information, it will not be passed to long-term memory, providing further support for the multi-store model and the idea of discrete components.


Peterson & Peterson used a sample of 24 psychology students, which is an issue for two reasons. Firstly, the psychology students may have encountered the multi-store model of memory previously and therefore may have demonstrated demand characteristics by changing their behaviour to assist the experimenter. Secondly, the memory of psychology students may be different to that of other people, especially if they had previously studied strategies for memory improvement. As a result we are unable to generalise the results of this study to non-psychology students.

Furthermore, it could be argued that Peterson & Peterson’s study has low levels of ecological validity. In this study participants were asked to recall three letter trigrams, which is unlike anything people would want to memorise in their everyday lives. As a result we are unable to apply these results to everyday examples of memory and are unable to conclude if the duration of short-term memory may be longer for more important information i.e. memorising a phone number.

However, Peterson & Peterson’s study was highly controlled and took place in a laboratory of Indiana University. As a result Peterson & Peterson had a high degree of control for extraneous variables, which makes their procedure easy to replicate.

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