Working memory capacity and chunking

Step 1 Warm-up recall

From M2.L1: what does task switching cost?

Your answer

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Step 2 Learning goal

By the end of this lesson you can:

• describe the limits of working memory (Foundation);
• count chunks in a sequence (Core);
• create chunks for a list of your own (Core).

Step 3 A familiar example

Try remembering 1 4 9 2 1 7 7 6. It is hard as eight digits. But as two famous years, 1492 and 1776, it is easy. The digits did not change; the chunks did.

Step 4 Clear explanation

Working memory holds and manipulates a small amount of information for a short time. Two features matter: it is small, and without rehearsal it fades within seconds (Peterson and Peterson, 1959). Early estimates put the span at about “seven, plus or minus two” items (Miller, 1956), but later work that controlled for chunking suggested about four chunks (Cowan, 2001). Estimates vary with the task and the person, so treat “about four” as a guide, not a fixed number.

A chunk is a meaningful unit that you already know. Chunking packs more information into one place.

The twelve digits 149217762026 are hard as twelve items but easy as three chunks if you know the years. Experts chunk well in their own field: a chess master sees a familiar pattern of pieces, not 20 separate pieces, and a doctor sees a pattern of symptoms. So working memory limits matter most to beginners, who have few chunks. For study this means learning key vocabulary and patterns first, so later material can be held in fewer chunks. The entry on working memory gives more background.

Step 5 Worked example (4 marks)

Chunk the letters U N E S C O W H O N A S A and count the chunks.

1. 13 letters is too many to hold one by one. (1 mark)
2. Group them: UNESCO, WHO, NASA. (1 mark)
3. Count the groups: 3. (1 mark)
4. Answer: 3 chunks, within a capacity of about 4. (1 mark)

Step 6 Learner practice (instant-marked)

Step 7 Recap

• Working memory is small and fades in seconds without rehearsal.
• Capacity is best counted in chunks, about four as a guide.
• Experts chunk using long-term memory.

Step 8 Exit ticket (ungraded)

Chunk the phone-like string 2 0 7 9 4 6 0 9 5 8 and count the chunks.

Your answer

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Step 9 Go further (Extension)

Read the entry on working memory and note one way to extend what you can hold.