Few activities are as cognitively demanding as writing, says psychologist Ronald Kellogg, PhD, a writing-cognition researcher at Saint Louis University. A comparison by Kellogg in his book "The Psychology of Writing" (Oxford University Press, 1999) shows that writing taxes the working memory system more than reading, and even such demanding laboratory tasks as memorizing lists of nonsense syllables. New research by Kellogg and others is adding to that finding, showing how planning, writing and revising can engage different facets of the working memory system.

When people compose, they primarily use their verbal working memory, rather than spatial working memory, according to research by Kellogg in press at Acta Psychologica. In his study, undergraduate students performed simple tasks that drew on different aspects of working memory, and some of the participants simultaneously attempted to write definitions of common nouns.

In one task, intended to tax verbal working memory, the participants would occasionally see a syllable, such as "ba," on their computer screen. They clicked a button if the syllable was the same as one they previously read. Another group of students simply identified whether a shape appeared in the same location on the screen as before.

The students who matched the syllables while also trying to write took 200 milliseconds longer to do so than the students who weren't attempting the two tasks at once. However, the students who, while writing, only had to take note of an object's location took no longer to do so than the students who could devote all their attention to the task.

This suggests that writing uses the verbal aspect of working memory but not the brain's spatial workspace, says Kellogg.

"The inner voice we subjectively experience when we write is showing up as a demand in verbal working memory," he says.

But while spatial memory may not be required for writing short definitions, it could be necessary for writing longer pieces or planning the shape of composition, according to David Galbraith, PhD, a psychology professor at England's Staffordshire University. Research by Galbraith published in "L1: Educational studies in language and literature" (Springer, 2005) shows that distracting students with a spatial memory task results in poorer outlines and, ultimately, essays.

In the study, Galbraith asked students to spend 15 minutes planning an essay. At the same time, some of the students also had to trace the path of a Velcro strip with a free hand.

The track-tracing students generated about half as many ideas as a control group of foot-tapping students, and they were less able to then organize their thoughts into an outline. The findings suggest that people represent their ideas visually when trying to structure their essays, Galbraith notes.

Taken together, the research shows that writing puts multiple and heavy demands on the mind's limited capacity to juggle different ideas simultaneously, says Kellogg.

"Even something as simple as making an agreement between a subject and a verb puts a demand on working memory," says Kellogg.

--S. Dingfelder