Whoa:

One way to measure working memory is to have subjects solve a list of equations (5 + 4 = x; 8 + 9 = y; 7 + 2 = z; and so on) while keeping the middle numbers in mind (4, 9 and 2 in the above example). Elite memory athletes can usually store seven items, the top score on the test the researchers used; the average for college students is around two.

“And college students tend to be good at this task,” said Dr. Roediger, a co-author of the new book “Make It Stick: The Science of Successful Learning.” “What I’d like to do is extend the scoring up to, say, 21, just to see how far the memory athletes can go.”

Yet this finding raises another question: Why don’t the competitors’ memory palaces ever fill up? Players usually have many favored locations to store studied facts, but they practice and compete repeatedly. They use and reuse the same blueprints hundreds of times, and the new images seem to overwrite the old ones — virtually without error.