Schaefer's team had 32 nine-year-olds and 32 adults (average age 25) complete the N-back working memory task in three conditions: walking on a treadmill at their own chosen speed; walking on a treadmill at a set speed chosen by the researchers; or sitting down. The N-back task requires that participants listen to a stream of numbers and indicate, in the easiest version, whenever the current number was the same as the number one back. For more difficult versions, it's a repeat of a number further back in the stream that must be spotted.
The headline finding was that the working memory performance of both age groups improved when walking at their chosen speed compared with when sitting or walking at a fixed speed set by the researchers. This was especially the case for more difficult versions of the working memory task, and was more pronounced among the children than the adults. So, this would appear to be clear case of mental performance actually being superior in a dual-task situation.
Why should the secondary task of walking aid, rather impair, mental performance? The researchers aren't sure of the mechanism, but they think the attentional pool tapped by a sensori-motor task like walking is likely separate from the attentional pool tapped by working memory. Moreover, physical activity increases arousal and activation, 'which then can be invested into the cognitive task,' they said.
What about the fact that memory performance wasn't improved when participants walked on the treadmill at a speed set by the researchers? The set walking speed was actually substantially slower than the participants' preferred speed so one possibility is that it wasn't rigorous enough to provide the increased arousal that could be beneficial to memory. Alternatively, perhaps the challenge of walking at a set speed is cognitively demanding, tapping the same attentional pool needed for the memory task.
Schaefer's team speculated that a useful application of their finding could be in relation to childhood ADHD. '...[H]yperactive children might also be able to profit from some type of consistent movement that does not require much attention, even though it is often argued that those children have more problems than healthy controls when they have to divide their attention between two concurrent tasks.'
Schaefer, S., Lovden, M., Wieckhorst, B., & Lindenberger, U. (2010). Cognitive performance is improved while walking: Differences in cognitive-sensorimotor couplings between children and young adults. European Journal of Developmental Psychology, 7 (3), 371-389 DOI: 10.1080/17405620802535666
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