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The Boston Globe

Opinion

Alex Beam

Four-bit recall

istockphoto/globe staff illustration

In his new book, “The Organized Mind,” McGill University neuroscience professor Daniel Levitin writes about filing systems: “The key to creating useful categories in our homes is to limit the number of types of things they contain to one or at most four (respecting the capacity limitations for working memory).”

This news about the four-bit brain didn’t surprise me, because I had heard psychologist Peter Doolittle’s 2013 TED talk on working memory. “We tend to remember about four things,” Doolittle said. “It used to be seven . . . but with functional memory it really is four.”

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And as we know from experience, memory is fleeting. “We can remember those four things for about ten to twenty seconds, unless we do something with it,” Doolittle explained. “Unless we process it, unless we apply it to something, or talk to somebody about it.”

Where was I? Oh, yes . . .

I find this all somewhat confusing, as I claim to remember Professor John Gabrieli explaining in a 1997 neuroscience lecture at Stanford that our brains had a 10-bit memory capacity. He suggested the telephone number as perfectly suited for ideal recall. I can indeed remember phone numbers, but my wife has memorized her 15-digit American Express card number, plus the four-digit security code, plus the expiration date.

In contrast, I can never remember my 14-digit Minuteman Library card number, which I use almost every day. However, I do recall several lines from the Chinese poem “The Shi-King,” assigned in fourth grade. (“Good men are bulwarks, while the multitudes are walls that ring the land . . .”)

So what can we remember? Four things? Seven? Ten? Who engineered this hardware, anyway?

Doolittle explained to me in an email that the seven-bit capacity refers to short-term memory (STM), or what cognitive psychologist George Miller called in a famous 1956 article “the magical number seven, plus or minus two.”

Scientists now generally talk about working memory, referring to information that the brain not only retains, but can use quickly in conjunction with other tasks. The classic example is remembering an address while driving and searching for the right street and house. In a separate email, Gabrieli, who now runs a lab at MIT, agrees that the scholarship has changed since I heard him speak 17 years ago: “Now the thought is that real STM capacity is about three/four items — for example, if people are reading a list of words, and get an unexpected memory test, they tend to remember the last three-four words out of STM (not seven-ish).”

What about my wife’s prodigious feat of AMEX memory? Both Levitin and Doolittle explain that her achievement belongs in the category of long-term memory, and can probably be ascribed to “chunking,” an infelicitous term coined by the aforementioned Miller. (Remember him?)

“The area code might be one chunk,” Levitin said, “a three-digit neighborhood prefix, another. So with all that chunking, the numbers you have to remember might consist of only six pieces of information: the area code (one), the prefix (one), and the four numbers (four).”

In the brilliant novella, “A Study in Scarlet,” Sherlock Holmes observed: “I consider that a man’s brain originally is like a little empty attic, and you have to stock it with such furniture as you choose.” Holmes never bothered to learn the names of the planets, because knowing them wouldn’t help solve crimes.

So if I had to sort through my brain attic, which info-bytes would I retain?

Seven items would be easy: My Social Security number; my wife’s birthday (mid-July, I think); my three sons’ names — a chunk, to be sure; and of course the one password that unlocks all of my computer and bank accounts.

If cerebral housecleaning required me to keep only four items, I would never part with my extensive and ever-growing Enemies List, which I update thanks to the helpful mnemonic SMERSHKGBOGPUNKVD. That combines my enemies’ surnames with acronyms of bygone Soviet security agencies.

I guess the “Shi-King” would have to go.

Wait! Thank heavens I remembered:

Correction: Last week I bungled the name of Great Britain’s World War II hero, James Howard Williams, known to history as “Elephant Bill.”

Alex Beam’s column appears regularly in the Globe. He can be reached at alexbeam@hotmail.com.
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