Cognitive Psychology - Duration in STM

Human Memory Human Memory Lesson 5

STM & Duration

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Key Study – STM & Duration

Peterson & Peterson (1959) Aim: • To test how long STM last when rehearsal is prevented.

Procedure: • Participants were briefly shown consonant trigrams (i.e., three letters such as CPW or NGV).

• Participants were asked to count backwards in three’s from a specified number to stop them thinking about the letters.

• After intervals of 3, 6, 9, 12, 15, or 18 seconds, participants were asked to recall the original trigram.

• The procedure was repeated several times using different trigrams.

Findings: • Participants were able to recall 80% of the trigrams after a three-second interval.

• Progressively fewer trigrams were recalled as the time intervals lengthened.

• After 18 seconds, fewer than 10% of the trigrams were recalled correctly.

Conclusion: • If rehearsal is prevented, information vanishes rapidly from STM. • Therefore, decay is the mechanism for forgetting in short term memory.

Criticisms: • Trigrams are rather artificial things to remember and may not reflect everyday memory. • It is possible; however, that interference from the counting task (not merely decay) caused the poor recall.

Methodical Issues •

This was a laboratory experiment carried out in a controlled environment. This study used a repeated measures design to avoid individual differences (participants served as their own control).

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However, there are some problems of interpretation with this study:

a) Trigrams are artificial things to remember and may not be a good way of testing how we remember things.

b) It is possible that the loss of information was more to do with capacity limitations then duration. The subsequent counting task might have pushed out (displaced) the trigram. c) It is also possible that the trigrams presented on earlier trials caused confusion (proactive interference) for the participants and so the later trigrams are incorrectly recalled. d) There are no ethical serious ethical issues in this kind of study but investigators need to have gained consent, informed participants about their right to withdraw and participants should be debriefed at the end of the experiment.