was not in working memory, the participant just randomly guessed," Rouder says."Each participant had a fixed capacity that could not be exceeded." That working memory had this "all or nothing" limitation came as something of a revelation to many experts in the field.
"I was surprised by this result, but find the study persuasive," says EEG Institute chief scientist Siegfried Othmer, a Woodland Hills, Calif.-based author of several books on therapies for attention deficit disorders (ADD and ADHD).
"If there is indeed such a hard limit on visual working memory capacity, then it becomes easier to discern the influence of attention and other factors on working memory performance."
University of Notre Dame associate professor of psychology Bradley Gibson says he's been "thinking a lot about these issues lately in my own research, and I really liked this paper."
Gibson, who studies visual cognition, perception and attention, found the Rouder-Cowan study "eloquent." His own work, he adds, reinforces their conclusions.
"The strength of this study lies in its analytic treatment of the findings," Gibson says. "Because of its analytic rigor, it may well provide one of the most precise estimates to date of the capacity of working memory."
One way to think of working memory, explains Barbara Ingersoll, an associate professor of behavioral medicine and clinical associate professor of psychiatry at West Virginia University, is the ability to retain a phone number long enough to accomplish a given task -- such as dialing a phone.Figuring out how working memory functions is important, she adds, because it could improve therapies for various attention deficit disorders.
Gibson, who has performed significant research on working memory in children with ADHD, concurs. "Having a precise measure of working memory is important," he says, "because weaknesses in working memory have been shown to underlie academic difficulties in reading comprehension and mathematical competence, as well as clinical symptoms of inattentiveness."
Nelson Cowan has long been a leader in this search for such measures. Long before his most recent paper, he was well known among psychology researchers for developing "Cowan's Formula," a measure that estimates memory capacity by linking the art of "guesstimating" to visual memory. He's also been a leading debunker of outdated working-memory hypotheses.