Trace decay is an explanation for forgetting in both LTM and STM. For STM, it suggests that if information isn’t rehearsed then the trace connections which would otherwise form an engram, simply fade away. For LTM, if information isn’t regularly rehearsed, then the engram will also fade away over time.

Brown Peterson task

Aim- To investigate the hypothesis that STM has duration of 20 seconds and if information isn’t rehearsed then it disappears.

Method- Participants were presented with sets of trigrams. Immediately after, participants heard a number which required them to count backwards from the number in threes (distractor task: to prevent rehearsal). The participants then had to recall the trigrams after intervals of 3, 6, 9, 12, 15 or 18 seconds.

Results- After a 3 second delay, participants could recall 80% of trigrams whereas after 18 seconds, participants could only recall 10% of trigrams.

Conclusion- Information held in STM is lost after 20 seconds without rehearsal.


§  It can’t be guaranteed that participants are counting down.

§  Low ecological validity as it is an artificial task so people do not recall trigrams in everyday life, therefore difficult to generalise.

§  May explain interference more than trace decay as it could have been the distractor task which caused the participants to forget.

Evaluation of trace decay

§  The theory doesn’t account for when someone can remember an event from a long time ago without rehearsing it regularly, so surely all our memories which we haven’t rehearsed would fade away over time.

§  It is very difficult to test trace decay without it resulting in interference.




Interference is an explanation for LTM which suggests that information can be forgotten due to confusion with previous or later information.

§  Proactive interference- Where information learnt earlier interferes with information learnt later. Where old memories disrupt new ones.

§  Retroactive interference- Where information learnt later interferes with information learnt earlier. Where new memories disrupt old ones.

Keppel and Underwood

Aim- To investigate the effects of proactive interference on recall.

Method- Participants were given a series of trials where they had to learn trigrams and then count backwards for 3, 9 or 18 seconds.

Results- On the first trial, performance was 100% but on the second and third trials, performance dropped.

Conclusion- The poor performance on later trials was down to proactive interference where the previous trigrams interfered with the current ones. The first trigram was remembered perfectly as there was nothing there to interfere with it.

Evaluation of interference theory


§  Most laboratory studies use nonsense symbols but when real words are use, the effects of interference are less noticeable.

§  Studies used to support the theory lack ecological validity as they are artificial and not common in everyday life so it’s difficult to generalise from the findings.


§  Most of the studies used to support the theory have a high validity and as they are done


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