Study: Peterson and Peterson (1959) short-term retention

Study: Peterson and Peterson (1959) Short-Term Retention

Ever wondered why you can remember a phone number just long enough to dial it, but if someone interrupts you to ask a question, the numbers vanish instantly? This famous study by Peterson and Peterson (1959) explains exactly why that happens! It is a key study in Topic 2: Memory because it explores the duration of our short-term memory.

Note: This study links directly to the Multi-store Model of Memory (Atkinson and Shiffrin), which suggests that if we don't rehearse information, it disappears from our short-term store.

The Aim of the Study

The researchers wanted to find out how long information stays in our short-term memory (STM) when we are not allowed to repeat it to ourselves (rehearse it). They specifically wanted to see if information in the STM fades away quickly over a short period of time.

The Procedure: How did they do it?

The researchers used \(24\) students as their participants. Here is how the experiment worked step-by-step:

1. Each student was shown a trigram. A trigram is a set of three consonants (for example, PXT or WFB).

2. Immediately after seeing the trigram, the student was given a three-digit number (like \(591\)).

3. They had to count backwards from that number in threes (e.g., \(591, 588, 585...\)) out loud. This was an interference task designed to stop them from rehearsing the trigram in their heads.

4. After a specific amount of time (the delay), a red light would signal them to stop counting and try to recall the trigram.

5. The delays used were \(3, 6, 9, 12, 15,\) and \(18\) seconds. Each student did several trials with these different time gaps.

Quick Tip: Think of the "counting backwards" part like a wall. It blocks the path for the information to be repeated, forcing the brain to rely only on the natural "holding time" of the short-term memory!

The Findings: Results and Conclusions

The results showed a very clear pattern: the longer the delay, the worse the students performed.

The Results:
• After a \(3\)-second delay, participants remembered about \(80\%\) of the trigrams correctly.
• After a \(6\)-second delay, this dropped to about \(50\%\).
• By the time they reached an \(18\)-second delay, fewer than \(10\%\) of the trigrams were remembered correctly.

The Conclusion:
Peterson and Peterson concluded that short-term memory has a very limited duration. If we are prevented from rehearsing information, it fades almost entirely after about \(18\) to \(30\) seconds. This supports the idea that STM is a separate store from Long-Term Memory (LTM), which can hold information for years.

Evaluating the Study: Strengths

High Reliability: The study used a highly standardised procedure. This means every participant was tested in the same way (same trigrams, same time intervals, same counting task). Because it was so controlled, other researchers can repeat the study to see if they get the same results.

Good Control: By using the counting task, the researchers successfully stopped participants from rehearsing. This allowed them to measure the true duration of the STM without the "cheating" of mental rehearsal.

Evaluating the Study: Weaknesses

Low Ecological Validity: The task was very artificial. In real life, we don't usually spend our time trying to remember random three-letter consonants while counting backwards in threes! This means the study might not tell us how memory works in everyday situations, like remembering a grocery list or a story.

Sample Bias: The participants were all students. Students might have better-practised memories or different study habits than the general population. This makes it harder to generalise the findings to older people or people who aren't in education.

Summary Checklist: Key Takeaways

• Aim: To measure the duration of STM without rehearsal.
• Task: Remember trigrams (consonants) while counting backwards in \(3s\).
• Main Result: Recall dropped from \(80\%\) at \(3\) seconds to less than \(10\%\) at \(18\) seconds.
• Conclusion: STM duration is about \(18-30\) seconds.
• Evaluation: Highly reliable and controlled, but lacked ecological validity (artificial task).

Common Mistake to Avoid: Don't confuse duration with capacity. Duration is about how long memory lasts (the focus of this study). Capacity is about how much it can hold (usually \(7 \pm 2\) items).