Aims: To measure the effect of inhibiting rehearsal on the duration of Short Term Memory (STM)
Procedure: Participants hear a list of trigrams (three-letter nonsense words), and then have to count, aloud, backwards in threes for a certain time (the IV in this experiment). After the time has completed, P's are tested on their recall of the trigrams
Findings: There was a marked negative correlation between the delay and the percentage of trigrams recalled by Participants; a delay of three seconds produced a mean score of almost 80%, but for a delay of eighteen seconds, the score dropped to 6%.
Conclusion: In the absence of rehearsal, STM's duration is very short.
Strength: These results have replicability; they have been reproduced many times.
Weakness 1: As Keppel & Underwood (1962) showed, the fact that Peterson & Peterson ran "practice" tests, it could be that some of these results were influenced by proactive interference
Weakness 2: Remembering trigrams is not an every day occurrence, and so it is questionable how much ecological validity these findings have.