Air Date: Week of April 16, 2004

Living on Earth’s Jennifer Chu reports on a study that provides a neurological explanation for the old adage “out of sight, out of mind.”

Transcript

CURWOOD: Just ahead: greening the city of the angels. First, this Note on Emerging Science from Jennifer Chu.

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CHU: Short-term memory can be a slippery fish. Since the 1960s, scientists have shown that the old adage “out of sight, out of mind” does, in fact, have a neurological basis. While our brains can register a staggering amount of what we see at any given moment, most of these visual details evaporate as soon as we close our eyes. The reason we can’t hold many images in mind is simple enough: our visual short-term memory is extremely limited and there’s a threshold for the amount of information we can store in our brain’s short-term memory box.

Little is known about how or why this is the case but researchers at Vanderbilt University now say they’ve solved the first part of this riddle. According to their study, one particular region of the brain, the posterior parietal cortex, is solely responsible for our limited visual recall powers. Moreover, they say we can actually quantify its limits. Researchers scanned the brains of 17 participants who were shown scenes containing one to eight colored objects. After a delay of just over a second, the subjects were asked about the scene they had viewed.

While the subjects were good at remembering all of the objects in scenes with four or fewer objects, their memories fumbled when asked to describe scenes containing more than four objects. The brain scans revealed that activity in the posterior parietal cortex increased as participants recalled up to four objects, and then leveled off as more objects were shown. Scientists suggest these results may represent how much visual information the mind can absorb. That’s this week’s Note on Emerging Science. I’m Jennifer Chu.

CURWOOD: And you’re listening to NPR’s Living on Earth.

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[MUSIC: Frifot “The Glutton” SUMMERSONG (Caprice Records – 1999)]