Fall 2008.
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Illumination magazine.
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Philosophers and scientists have for centuries puzzled over the workings of human memory, an aspect of human consciousness that, at least since the time of Aristotle, has been considered one of nature's most complicated creations.

But is it possible the world's great minds have spent the last two millennia over-thinking memory's complexities? A recent study by two University of Missouri researchers suggests this may in fact be the case -- at least for one important aspect of memory.

Multimedia: Memory at Work.Jeff Rouder, an associate professor of psychology, and Curator's Professor of Psychology Nelson Cowan have found our "working memory," that faculty of the brain that allows us to retain information of immediate importance to us, may be very simple indeed.

"Most people believe the human mind is incredibly complex," Rouder says. "We were able to use a relatively simple experiment and look at how many objects can be in maintained in the human conscious mind at any one time. We found that every person has the capacity to hold a certain number of objects in his or her mind."

Their study, published in the April 22 edition of the Proceedings of the National Academy of Sciences, determined that the average person remembers a mere three or four things at any one time.

These recalled things, items such as numbers, letters, colors, and names, are then stored in the mind as discrete, well-defined bits of information. It's similar to the way a computer works, Rouder and Cowan say.

The researchers arrived at this conclusion after devising a unique version of a simple memory experiment. First, they used a computer to quickly show study participants an array of two, five, or eight differently colored squares. When quizzed by the researchers on arrays of two squares, subjects could typically remember the colors and, later, determine whether colors changed or appeared out of sequence. Other studies show this for up to four squares.

Add a fifth square, however, and working memory begins to falter. Increase beyond five, and working memory fails increasingly often. Study participants usually provided answers anyway but, thanks to a model Cowan devised that Rouder calls "exceptionally simple and elegant," the two researchers soon figured out subjects sometimes didn't have a clue.

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