In Brief

The more people exercise their working memory, the more items they can store in it--but only up to about four items, suggests a study from the November issue of APA's Journal of Experimental Psychology: Learning, Memory and Cognition (Vol. 30, No. 6).

To reach that finding, Syracuse University psychology professors Paul Verhaeghen, PhD, and John Cerella, PhD, and student Chandramallika Basak investigated the capacity of working memory--which they say before practice can be limited to one item. The research team tested the working memories of five adult participants during 10 one-hour sessions spread over five days.

The participants performed an "n-back task," which presented them with one to five columns of single-digit numbers on a computer monitor. Only one number was visible at a time, each for only two seconds.

After seeing the first row of numbers, participants indicated whether each successive number displayed in new rows matched the number previously displayed in the same column. Each hour-long session contained 55 trials with 20 numbers per trial, generating over 10,000 responses.

In the first session, participants responded much faster for the one-column version than for the more complex, multicolumn versions, which were similar to each other in response times--suggesting that participants could immediately access only one column in working memory.

But response times between one- and four-column trials flattened out by the seventh session and were stable through the 10th session. Now, the jump appeared between the four-column and five-column trials, demonstrating that the participants' focus of attention had expanded fourfold. The results, Verhaeghen explains, suggest a trade-off: As participants practiced the n-back task, they needed to devote fewer cognitive resources to it, allowing them to expand their working memory.

"This is just like what happens in everyday life," Verhaeghen says. "Practice on any given task--driving, shooting hoops, taking notes in class--allows you to do several things at once."

The findings show it's normally challenging for people to shift the focus of their attention between items in working memory, says Verhaeghen, who offers this example: People count how many pennies, nickels, dimes and quarters are in a pile of coins by sorting and counting each denomination separately, rather than counting coin by coin, simultaneously maintaining running totals for all denominations. That's because it requires too much mental effort to keep more than one total active in their focus of attention. When focused on updating the count of pennies, the nickel count slips into passive storage.

But practice may not work in all cases and it has its limitations, he added: "Four [items] seems to be the limit. It's a fundamental characteristic of human working memory."