ºÙºÙÊÓƵ

People's short-term "working memory," which allows the brain to stitch together sensory information, retains a limited number of high-resolution images for a few seconds, rather than a wider range of fuzzier impressions, ºÙºÙÊÓƵ researchers say.

As the eyes flit from object to object (because people rarely move their eyes smoothly), the visual system briefly shuts off to cut down visual "noise," said Steven J. Luck, professor of psychology at the ºÙºÙÊÓƵ Center for Mind and Brain. So the brain gets a series of snapshots of about a quarter-second, with brief gaps in between.

The working memory system smoothes out this jerky sequence by retaining memories from each snapshot so that they can be blended together. These memories typically last just a few seconds, Luck said.

"We use working memory hundreds of thousands of times each day without noticing it," Luck said. The system also seems to be linked to intelligence, he said.

Luck and postdoctoral researcher Weiwei Zhang, who described their findings in a paper published online by the journal Nature, set out to determine if the working memory stores a fixed, limited number of high-resolution images, or constitutes a more fluid system that can store either a small number of high-resolution images or a large number of low-resolution images.

The researchers showed volunteers a pattern of colored squares for a tenth of a second, and then asked the test subjects to recall the color of one of the squares. Sometimes the subjects would be completely unable to remember the color, and they just clicked at a random location on a color wheel. When a subject could remember the square, he or she usually picked a color that was quite close to the correct color.

Zhang developed a technique for using these responses to quantify how many items a test subject could store in memory and how precise those memories were. The evidence showed that working memory acts like a high-resolution camera, retaining three or four features in high detail. The brain then links those features.

People who can store more information in working memory have higher levels of "fluid intelligence," the ability to solve novel problems, Luck said. Working memory is also important in keeping track of objects that are temporarily blocked from view, and it appears to be used when people need to recognize objects shown in unfamiliar views.

Outside the visual domain, working memory is used for storing alternatives or intermediate values, for example when adding a string of numbers together, Luck said. It also appears to play an important role in learning new words, perhaps by allowing the sound of a new word to remain active in the brain until a long-term memory can be formed.

Luck and Zhang are now interested in how working memory operates in people with conditions such as attention deficit-hyperactivity disorder and schizophrenia, and those who have problems in perception and cognition.