Peterson and Peterson (1959)

• Peterson and Peterson (1959) studied the duration of the STM.
• Aim

  To test how long the STM lasts when rehearsal is prevented.
• Procedure:

  • Participants were presented with a set of trigrams (nonsense syllables in sets of three, e.g. CPZ, MQD) which they were then asked to recall in order after a delay of increasing 3 second intervals. 3, 6, 9, 12, 15, 18...
  • In order to prevent rehearsal, participants were given an interference task of counting backwards in threes from a random three digit number to prevent rehearsal (Brown-Peterson technique)
  • Recall had to be 100% accurate and in the correct order to be counted as correct

  
• Findings:

  • Only 90% of trigrams were recalled correctly after around a 3 second delay between recall.
  • Only 5% of trigrams were recalled correctly after an 18 second delay.
• Conclusions

  The memory trace in the STM just about disappeared after 18 seconds. Information held in the STM is quickly lost without rehearsal. This supports the hypothesis that the duration of the STM is limited to between 20-30 seconds.
• Evaluation of Peterson and Peterson (1959)

  The trigrams are an artificial stimulus and trying to memorise consonant syllables is not something that reflects everyday memory so we can't generalise to real life where we often try to make things we remember more meaningful. Thus, P+P lacks ecological validity. However, sometimes we do try to memorise fairly meaningless things such as phone numbers.
• Evaluation of Peterson and Peterson (1959)

  It may be that interference for earlier trigrams may have caused the poor recall, not simply decay, there are studies which show that we do forget to interference.
• Evaluation of Peterson and Peterson (1959)

  The research method employed allows us to see that time passing in increasing 3 second intervals (IV) was directly reducing the recall of the trigrams (DV), thus establishing a cause and effect relationship between time passing in increasing intervals of 3 and the recall of trigrams.