You may think you remember every nook and cranny where you looked for those lost car keys. But a report in the current Nature suggests otherwise: The brain, it seems, does not memorize transient snapshots of the world around us.
Psychologists Todd Horowitz and Jeremy Wolfe of Brigham and Women's Hospital and Harvard Medical School asked subjects to find a single letter T in a field of L's shown on a screen. First the researchers flashed repeatedly the same configuration of letters for fractions of a second until each person spotted the T. Then the subjects watched a series of displays that were constantly rearranged, with the T in different positions during each short viewing period.
The researchers measured how much longer it took each subject to find the T in a sea of various numbers of L's. They reasoned that if the brain were recording the position of each letter, shuffling the displays should drastically slow the search because subjects would initially exclude areas on a new display that did not include a T on the previous display. However, shuffling the displays didn't slow the search at all--suggesting that the subjects were starting their search from scratch from one display to the next.
"It's certainly an important finding, and unexpected," says Harvard psychologist Patrick Cavanagh. "The common sense thought would be that you'd remember where you've been." But, he says, in hindsight this kind of forgetfulness does make sense. If you are swatting flies, for example, it may be more efficient to keep looking and swatting, than remembering where all the flies were. "We may be faster at forging ahead than remembering," Cavanagh explains.