Duration of STM & LTM

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Duration: A measure of how long a memory lasts before it's no longer available. STM has a very limited duration whereas LTM has potentially unlimited duration.

Duration is a key difference between short term memory and long term memory.

Duration of STM

STM is used when we need to remember something for a short period of time, an example of this is a seven digit phone number - this remains in the STM due to repetition however once dialled it is no longer needed, and once the conversation starts, it begins to fade.

Most keep their information in their STM via rehearsal (saying something over and over to keep re-presenting it to the STM) - this is one way of keeping the memory active. Such verbal rehearsal can lead to the memory being stored in the short-term memory store, and then eventually become long term.

Key Study: Peterson & Peterson

Margaret and Lloyd Peterson conducted a study to test the duration of STM.


  • There was a sample of 24 students who were attending their university.
  • Each participant was tested over eight trials
  • Over each trial, the participants were given a consonant syllable and a three-digit number (e.g HBS 365)
  • They were asked to recall the syllable after a retention syllable of 3, 6, 9, 12, 15, 18 seconds.
  • During the retention interval; they had to count backwards from the three-digit number (in either 3s or 4s) to prevent rehearsal from taking place.


  • On average, participants were 90% correct over 3 seconds.
  • They were 20% correct after 9 seconds.
  • They were 2% correct after 18 seconds.
  • This suggest that STM has a very short durarion less than 18 seconds, if verbal rehearsal is prevented.


- This study lacked ecological validity because the stimulus material was artifical. Trying to memorise consonant syllables does not truly reflect most everyday memory activities where what we are trying to remember is meaningful. However, we do sometimes try to remember meaningless things, such as groups of numbers or letters as in a phone number or post code. This means the study does have some relevance to everyday life.

- One problem with this study is that the


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