When a person tries to memorize words or numbers, they rehearse the item to remember it for a longer time. In this experiment, rehearsal was prevented leading to decay in memory.
Aim
To investigate the duration of short-term memory.
Lloyd and Margaret Peterson aimed to test the hypothesis that information that is not rehearsed is lost quickly from short-term memory.
Procedure
A lab experiment was conducted in which 24 participants (psychology students) had to recall trigrams (meaningless three-consonant syllables), such as TGH, CLS.
The trigrams were presented one at a time and had to be recalled after intervals of 3, 6, 9, 12, 15 or 18 seconds respectively for each trial.
No two successive trigrams contained any of the same letters.
After hearing a trigram, participants were asked to count backward in threes or fours from a specified random digit number until they saw a red light appear (then they recalled the trigram). This is known as the Brown Peterson technique, which aimed to prevent rehearsal.
The independent variable was the time interval between hearing the experimenter say the trigram and the participant recalling the trigram (after seeing a red light), e.g. 3, 6, 9, 12, 15, or 18 seconds.
The dependent variable was the number of trigrams correctly recalled by the participants after every trial. There were six trials in total.
Findings
Their results showed that the longer each student had to count backwards, the less well they were able to recall the trigram accurately.
- After 3 seconds 80% of the trigrams were recalled correctly.
- After 6 seconds this fell to 50%.
- After 18 seconds less than 10% of the trigrams were recalled correctly.
Conclusion
Short-term memory has a limited duration (of about 18 seconds) when rehearsal is prevented. It is thought that this information is lost from short-term memory from trace decay.
The results of the study also show the short-term memory is different from long-term memory in terms of duration. Thus supporting the multi-store model of memory.
If a person is not able to rehearse information, it will not transfer to their long-term memory store.
Critical Evaluation
In this study, the researchers used fixed timings for participants to count backwards from. They also eliminated noise and other factors that could have had an influence on memory.
The research can therefore be said to have good control, using standardized procedures to make sure all participants experienced the same process. This means that the study is scientific because it can be replicated and the reliability of the findings can be checked to make sure they were not a one-off result.
However, the experimental method lacked mundane realism and external validity as they used very artificial stimuli (i.e., people do not try to recall trigrams in real life).
Also, this study only considered short-term memory duration for one type of stimuli. They did not provide information about other types of stimuli such as pictures and melodies.
One important practical application of this study is that it demonstrates how interference in the form of verbal distractions can affect our ability to retain information.
This implies that when we are revising for an exam or trying to memorize a shopping list before we pop to the shop, we should take care to avoid distractions.
References
Peterson, L.R., & Peterson, M.J. (1959). Short-term retention of individual verbal items. Journal of Experimental Psychology, 58, 193-198
FAQs
What is the Brown Peterson task method?
The Brown Peterson task is a cognitive psychology experimental method used to study the duration of short-term memory. Participants are presented with a series of items to remember, and then engaged in a distracting task to prevent rehearsal. They are later tested on their ability to recall the original items.
What was the dependent variable in Peterson and Peterson’s 1959 study on short-term memory?
The dependent variable in Peterson and Peterson’s 1959 study on short-term memory was the participants’ ability to recall and correctly reproduce the trigram (three-letter nonsense syllables) after a specified delay interval. The researchers measured the accuracy of recall to assess the duration of short-term memory.
What was the independent variable in Peterson and Peterson’s 1959 study on short-term memory?
The independent variable was the length of the delay interval between the presentation of the trigram (three-letter nonsense syllables) and the recall task. Different delay intervals, such as 3, 6, 9, 12, 15, or 18 seconds, were used to examine the effect of time on the decay of information in short-term memory.
