Duration of STM - Peterson and Peterson 1959


  • A strength of this study is that it has a high degree of control. This is because it is a laboratory experiment, and so the researchers had strict control over variables. They could therefore be sure that chnages in the DV (number of trigrams recalled) were due to changes in the IV (time delay).
  • Another strength of the study is that the findings are reliable. For example, Sebrechts et al 1989 asked pp to unexpectedly recall words either immediately after seeing them or some time after seeing them. The pps were not expecting to to have to recall the words so should not have been rehearsing them. It was found that recall was zero even after 4 seconds. Whilst this study shows that the STM has a much shorter duration than suggested by Peterson and Peterson it does support the overall idea that the duration of STM is very limited when rehearsal is prevented.


  • A limitation of the study is that it is low in ecological validity. Whilst the experimental method used gave the researchers a high degree of control over all variables it can be argued that the set up was very artificial. It is not a common occurrence to learn trigrams whilst counting backwards in threes and so the study may tell us little about the duration of STM in real life.
  • A final limitation of the study is that it lacks population validity.This is because the participants were all students. Therefore, the findings may not generaliseto the wider population. It should also be considered that the sample size was also fairly small which again limits the ability to generlise the findings.


Conclusions - The memory trace in the STM has just about disappeared after 18 seconds. Information held in the STM is quickly lost without rehearsal. This supports the hypothesis that the duration of STM is limited to approximately 18 seconds. They also conclude that this is evidence that the STM is distinct from the LTM as LTM has a much longer LTM


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