When someone reads you a phone number, you hold it in your head for a few seconds while you dial. That short-term holding place is called working memory. Think of it as a small workbench: you can work on a few things there, but it fills up fast.
In 1956 the psychologist George Miller noticed that people could repeat back about seven items, give or take two. Later work, gathered by Nelson Cowan in 2001, showed that when people can't rehearse or group the items, the true limit is closer to four chunks, usually three to five.
Key idea
Working memory holds about four chunks. A chunk is any unit you already know as one thing: a digit, a word, a familiar year like 1776.
Why it works
If the bench holds about four things, a twelve-digit number is too much as twelve digits. But if those digits form three years you already know, the bench only has to hold three things.
Worked example: Worked example
You hear the list: cat, lamp, river, pencil, cloud, drum, apple, shoe. About how many can most people hold at once without grouping?
- Working memory holds about four chunks.
- Eight unrelated words is about twice that.
Answer: About four, so the list needs grouping or practice.
Common mistake
Thinking a bigger effort will hold more. The workbench is small for everyone. The trick is to make each item on it bigger by chunking, or to move it into long-term memory with practice.