Open the app
  1. Home
  2. Lessons
  3. GCSE Psychology
  4. Key study: Peterson and Peterson (1959) short-term retention

Key study: Peterson and Peterson (1959) short-term retention

🎬 The doodle video for this lesson is coming soon. Subscribe on YouTube to see it first.

How long does information last in short-term memory if you cannot repeat it to yourself? Peterson and Peterson designed a clever experiment to find out.

Aim and procedure

Aim: to investigate how long information lasts in short-term memory when rehearsal is prevented.
Sample: 24 students from an introductory psychology course in the USA.
Procedure: a laboratory experiment. Participants heard a trigram (three consonants, such as CHJ), then a three-digit number. They immediately counted backwards in threes (or fours) from that number, which stopped them rehearsing the trigram.
After an interval of 3, 6, 9, 12, 15 or 18 seconds, they tried to recall the trigram.

Results and conclusion

Results: the longer the interval, the worse the recall. Recall fell from about 80% correct after 3 seconds to about 10% after 18 seconds.
In a second part, participants who were allowed to repeat the trigram out loud for longer recalled it better.
Conclusion: without rehearsal, information in STM is lost very quickly, in under about 20 seconds. Rehearsal is needed to keep information in STM. This supports the multi-store model.

Strengths and weaknesses

Strengths: a controlled laboratory experiment with a standardised procedure, so it can be replicated and cause and effect can be shown. Trigrams avoid meaning, so participants could not easily link them to existing knowledge.
Weaknesses: trigrams are artificial, so the study may lack ecological validity: we usually remember meaningful information. Forgetting may have been caused by interference from earlier trigrams or the counting task, not by information fading. All participants were students, so the sample is limited.
Worked example

Why did participants count backwards in threes?

  1. Counting backwards uses STM and takes attention.
  2. This stops participants repeating (rehearsing) the trigram.

Answer: To prevent rehearsal, so the researchers could measure how long information lasts in STM without it.

Key idea

Peterson and Peterson gave 24 students trigrams and stopped rehearsal by counting backwards. Recall fell from about 80% at 3 seconds to about 10% at 18 seconds. STM duration is short without rehearsal. It was well controlled but artificial.

The interactive lesson includes the diagrams for this topic.

Check you have got it

Answer 7 quick questions with instant marking. If you get one wrong, GCSE-ready shows you why and gives you another go. It is free, and you do not need an account.

Practise this lesson free (7 questions)All GCSE Psychology lessons