How much can your short term memory hold?

In 1956, a cognitive psychologist at Princeton University named George A. Miller published what would become one of the most frequently cited papers in his field. His ideas were so popular that you’ve probably heard them even if you’ve never read his name. He’s responsible for what’s known as Miller’s law: at any given time, the average human can only hold about seven items in their short-term memory.

What you might not know about Miller’s trailblazing paper is that it was hilarious, as far as academic publications go. Entitled “The Magical Number Seven, Plus or Minus Two: Some Limits on our Capacity for Processing Information,” it began, “My problem is that I have been persecuted by an integer. For seven years this number has followed me around, has intruded in my most private data, and has assaulted me from the pages of our most public journals … Either there really is something unusual about the number or else I am suffering from delusions of persecution.” (He reportedly threw the paper together from multiple areas of his research after being cajoled into giving a talk for a psychology association, which could explain the tongue-in-cheek style.)

The integer he wrote about, of course, was 7. He noticed over and over that no matter what the subject matter, people were only able to hold on to about seven units of new information, “plus or minus two” — that is, roughly five to nine items. He explained how when people were asked to identify individual musical tones, they did okay when they had two or three to choose from, but started getting confused once the number of choices exceeded six. When people had to remember a list of random words in order, that list could be as long as seven words long before they got confused. The same was true for lists of digits. Even when given tests with lots of variables, like the sweetness and saltiness of various water samples or the locations of dots on a square, people tended to hit their accuracy limit around seven … plus or minus two.

That seven-item limit is what most people talk about. What’s less widely known, though, is Miller’s idea of “chunks.” That is, you might be able to recall seven digits or letters, but you’re also able to recall seven numbers, words, or even phrases. If you “chunk” the information into familiar units, you can remember them as individual items. For example, “FBICIANSAIRS” is 12 letters long — much longer than Miller’s law says you should be able to remember. But if you’re familiar with those US government acronyms, it’s just four chunks long: FBI, CIA, NSA, IRS. Likewise, your phone number is 10 digits long, but you remember it in hyphenated chunks.

That detail is key to overcoming the limits of Miller’s law. If you need to memorize something quickly, your best bet is to organize it into familiar chunks. That’s why time-honored memorization techniques like mnemonic devices work so well. For example, the eight planets of Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune pushes Miller’s upper limit. But “My Very Eager Mother Just Served Us Nachos” is a single sentence. Remember that individual chunk, and you can remember the order of all eight planets. In that way, your short-term memory is kind of like a suitcase: it can only fit so much, but if you know how to pack, you can maximize the space you have.

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