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The April issue of Wired UK gives a top ten list of clever—or, in some cases, downright disturbing—titles of scientific papers, as identified by this blog over at Discover. The list includes such gems as "Swearing as a response to pain," "The nature of navel fluff," and, uh, "Fellatio by fruit bats prolongs copulation time."
The Headcase humbly proposes a paper from the February issue of Current Directions in Psychological Science: "The Magical Mystery Four." In it, Missouri psychologist Nelson Cowan not only spins a name from one of John, Paul, George, and Ringo's finest albums, he also indirectly explains the nonexistence of a Fifth Beatle: Working memory, it turns out, is limited to roughly four pieces of information at a time.
Sorry, Pete.
Working memory is generally defined as the "temporarily active" thoughts people can keep in their head at a given time. As Cowan points out, this type of memory comes in handy while reading (to retain ideas presented earlier in a text), solving basic problems—even planning our days.
To define the limits of working memory, psychologists must run tests that prevent people from using mnemonic tricks. Past studies, for instance, have presented a running list of items to participants without letting them know when the list will end. When the list abruptly stops and participants are asked to recall the last few items, only three to five bits of information typically come to mind. This finding holds true in many cases, says Cowan:
With similar results across many types of materials and tasks, we believe that there truly is a central working memory faculty limited to 3 to 5 chunks for adults, which can predict mistakes in thinking and reasoning.
There are several theories behind the purpose of this limit. One is that it would be "biologically expensive" for our brains to retain more than a few working items. The more information one must encode, Cowan points out, the more likely brains might be to confuse details—turning a red circle and blue square into a red square and blue circle, for instance.
Another theory holds that our brains do best when wading through information with a beginning, middle, and end, suggesting benefits to three- or five-item lists, which averages out to four. Beyond five, the items in a list may lose distinctiveness.
Cowan considers a vast body of recent literature—much of it his own—in drawing his conclusions:
... there is an underlying limit on a central component of working memory-typically 3 to 5 chunks in young adults. ... There are probably factors of biological economy limiting central capacity, but in some ways, the existing limits may be ideal, or nearly so, for humans.
Speaking of ideal, or nearly so:
(Image: WikiCommons)
