One of my graduate school mentors noted that if he was walking when presented with a really difficult cognitive challenge, he would stop, as though walking drew, however slightly, on his attention. Rousseau, in contrast, claimed “I can only meditate when I am walking.”
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The advent of the treadmill desk makes the question of walking and cognition more urgent. Okay, there may be health benefits, but if walking is not fully automatic, it siphons away some of your thinking capacity; it demands multitasking, so why put one in the workplace? 

Researchers have caught up to business trends, and a couple of recent studies indicate that dedicated office walkers can relax—treadmills don’t seem to compromise cognition. Probably.

In one, researchers administered well-normed measures of working memory and executive function (digit span forwards and backwards, digit-symbol coding, letter-number substitution, and others) to 45 college undergraduates. Each completed the tasks while sitting, standing, and walking (in random order), with 1 week elapsing between sessions. Participants could set the walking speed as they preferred, between 1 and 3 km/hour. Performance on the working memory/executive function tasks was statistically indistinguishable in the three conditions.

That study had people walk (or not) and measured the impact on working memory. Another approach is for researchers to tax working memory (or not) and observe the impact on walking. Other researchers used that method, having subjects either just walk (again, at a self-selected pace), or walk while performing a working memory task, or walk while reading. Researchers recorded several aspects of gait, focusing on variability. Again, they found no evidence of interference.

The neurophysiology of walking would seem consistent with these results. Humans have central pattern generators in the spinal cord—neural circuits that, even in the absence of input of the brain, can generate patterns of flexion and extension in muscles that look like walking. Thus, if the spinal cord can handle walking on its own, it’s easy to see why walking is not compromised when the brain is doing something else.

But central pattern generators set up pretty crude motor output; locomotion (like all movement) requires close monitoring of perceptual feedback (from vision, from balance) which is used to fine-tune walking movements (For a review, see Clark, 2015). We notice the need for perceptual information when we walk on ice, and for motor tuning when we pick our way through a rocky beach, but the fine-tuning goes on in a less obtrusive way in everyday situations. To get a feel for that, find yourself a nice long hallway, pick a spot about 50 feet away, and walk towards it with your eyes closed. If walking were a completely automatic program that could run without visual input from the brain, this would be no problem, yet most sighted people feel uneasy just a few steps in.

So if walking actually can’t run with total automaticity, why does treadmill walking show no attentional cost?

It may be that there is a cost, but it’s so small that it’s not detected in these experiments. And that may mean it’s not worth worrying about. Follow-up experiments with greater statistical power to detect small effects would be needed to address that possibility. Three other caveats are worth considering before we all buy treadmill desks.

First, the studies to date have been of relatively brief duration—less than an hour. It’s possible that subjects can with some effort of concentration, walk without cognitive cost for a short period of time, but a few hours would reveal a deficit; tiredness might make walking a little sloppy, and thus more attention-demanding.

Second, at least one study has shown a movement task (key tapping) was compromised when people walk (Oblinger et al, 2011). That’s not an effect of attention, but of trying to do two motor actions at once, like rubbing your stomach while patting your head. Hence, although office activities like typing or data entry have not been tested on treadmills, I’d be willing to bet they would be compromised. 

Third, my graduate mentor and Rousseau may have been talking about different types of thought. My mentor referred to answering a question, whereas Rousseau may have meant more creative thought. Walking may not be helpful when the environment presents pressing problems in need of timely answers. But a meandering gait may promote meandering thought, which in turn promotes creativity. The latter has not be tested on office treadmills either.

Researchers emphasize there are very few circumstances in which you can do two things at once without cost (relative to doing each on its own). Yet some drivers sneak a look at their phone while on the road, and some students have the television playing while they complete an assignment.

Why? One possibility is that they don't understand the cost of multi-tasking very well. A new study (Finley, Benjamin, and McCarley, 2014) investigated that possibility.

Subjects initially practiced a tracking task: a small target moved erratically on a computer screen and the subject was to try to keep a mouse cursor atop it.

Interleaved with practice on the tracking task, subjects practiced a standard auditory N-back task: they heard a series of digits (one every 2.4 seconds) and were asked to say whether the digits matched the one spoken 2 digits earlier (or in other versions of the task, 1 digit or 3 digits earlier).

After a total of 3 phases of practice for each task, subjects were told that they would try to do both tasks at the same time. They were told to prioritize the tracking task; just as a driver must keep the car in the lane, they should do their best to keep the cursor near the target, but they should do their best on the N-back task.

Then subjects got feedback on their performance on the three phases of tracking task (expressed as percent time they had the cursor on the target) and they were asked to predict their performance on the tracking task when simultaneously doing the N-back task.

The results showed a significant drop in tracking performance when subjects had to do the N-back task at the same time. What did subjects predict?

Subjects did predict a decrement. What they could not do was predict the size.

The graph shows the correlation between the predicted decrement in tracking performance and the actual decrement.

Subjects were not just wildly guessing. Their predicted performance in the dual task situation was related to their performance in the single-task situation, as shown here:

So to make the judgment "how much will it hurt my tracking performance to add a second task?" subjects take their single-task tracking performance and subtract something. . . but the "something" is not accurate.

The analogy to typical dual-task situations is not that great. In this case, I have never performed the two tasks simultaneously and am asked to guess at performance when I do. When a student decides to watch television while completing an assignment, he very likely has completed those tasks in a dual-task situation.

This means he has two ways of predicting his performance: one would be guessing at the dual-task cost, and this experiment shows that although subjects know there is some cost, they are terrible at predicting its size.

The second way students could predict what will happen if they multitask while working is based on their memory of similar situations. But the feedback students get in this situation is unclear. First, the feedback is significantly delayed, relative to when the work is completed. Second, every assignment varies (and so do tv programs) so the student might attribute bad performance to one of those variables (although I don't know of any study showing no cost to background television).

But there is another interpretation of students' choice to multitask.  They know their performance will suffer, they know they don't know how much it will suffer, and they don't care.


Reference:
Finley, J. R., Benjamin, A. S., & McCarley, J. S. (2014). Metacognition of multitasking: How well do we predict the costs of divided attention? Journal of Experimental Psychology: Applied, in press.