Peterson and Peterson (1956)

• Researched duration of STM
• Used consonant syllables such as BNT in their research
• Used counting backwards as a means of preventing rehearsal
• Found that STM lasts about 18secs
• Aim: To investigate how different short intervals containing an interference task affect the recall of items presented verbally, and to infer the duration of STM.
• Method: The participants were 24 male and female university students. The verbal items tested for recall were 48 three-consonant nonsense syllables (such as JBW or PDX) spelled out letter by letter. These have since been named 'trigrams". There were also cards containing three-digit numbers (such as 360 or 294).
• The researcher spelled the syllable out and then immediately said a three-digit number. The participant had to count down backwards in either 3s or 4s (as instructed) from that number. This was to prevent repetition of the trigram by the participant.
• At the end of a preset interval of between 3 and 18 seconds a red light went on and the participant had to recall the trigram.
• Results: 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.
• Conclusion: STM has a limited duration ofapproximately 18 seconds. Furthermore, if we are unable to rehearse information it will not be passed to LTM, providing further support for the MSM and the idea of discrete components.
• Trigrams cometExperiment 1 Relationship between the length of theand the mean percentage of trigrams recalled correctly12