In one scene of the 1999 movie The Blair Witch Project, three film students searching for a legendary creature hike for hours only to end up at the spot where they had started.
Their misfortune is not just a suspenseful twist in a fictional world, says psychologist Jan Souman of the Max Planck Institute for Biological Cybernetics in Tübingen, Germany. Given no external cues to direction, people trying to walk straight over unfamiliar terrain end up doing intermittent loop-de-loops, Souman and his colleagues report in a paper published online August 20 in Current Biology.
Circular walking occurs when people have to rely solely on bodily cues, such as rotational shifts and joint movements, to estimate the location of “straight ahead,” Souman hypothesizes. As random errors in bodily feedback accumulate, a person eventually drifts to one side or the other. A walker dependent on bodily cues may first make a circle to the right, drift back to a straight-ahead direction, start to zigzag and then make a circle to the left.
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“You may think that you’re walking in a straight line, but in fact the direction you’re walking in is drifting more and more away from straight ahead, making you walk in circles,” Souman says.
That’s “a simple but elegant” proposal for how walking without any external directional signs can lead people in circles, remarks psychologist Roberta Klatzky of Carnegie Mellon University in Pittsburgh.
In these situations, people start to walk in circles after travelling only about the length of a football field, Souman’s team finds. Researchers are now trying to mathematically model how random errors in heading yield systematic movements such as circular walking.
Klatzky led an earlier study in which many blindfolded adults veered toward the right or left, without circling, while traversing almost half the length of a football field. She initially attributed this finding to a biological tendency to turn in one direction, perhaps because one leg is slightly longer or stronger than the other. In Souman’s study, most individuals circled to both the left and right within the same trial, undermining Klatzky’s proposal.
Psychologist John Rieser of Vanderbilt University in Nashville calls the new findings exciting. He and his colleagues have found that blindfolded people veer off course but don’t circle when walking up to 100 meters across a grassy field. But cues from the ground, such as variations in grass length in an otherwise predictable environment, may have reduced veering from a straight line, Rieser says.
“I suspect that one’s subjective sense of straight ahead, and up-down too, are easily changed by environmental conditions,” he remarks.
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Souman wanted to test whether people wander when lost and, after meandering back to where they started, erroneously think that they have walked in a circle. His team first instructed three men—ages 24, 35 and 41—to walk in a straight direction in part of the Sahara desert. Each man set out from a different starting point, trailed at a distance by an experimenter in an all-terrain vehicle. Over 2 ½ to 3 ½ hours, walking trajectories were recorded by GPS receivers that the men carried in backpacks.
Two men walked during the day, with the sun visible. They veered off course but did not go in circles. One man walked at night during a full moon. After clouds hid the moon, he made several sharp turns in the same direction, nearly bringing him back in the direction from which he came.
In a second experiment, six college students walked for about four hours in a dense German forest where the landscape provides no clear cues to direction. Four of them walked on an overcast day. GPS data showed that each of those students walked in a series of circles. Three didn’t notice when they repeatedly crossed their own paths.
The other two students walked on sunny days. Both followed an almost perfectly straight course, except during brief periods when clouds blocked the sun.
Animals such as bees and pigeons compensate for changes in the sun’s position as they fly from one spot to another. People may do the same while walking, Souman speculates.
In a third experiment, 15 blindfolded college students tried to stride straight forward in a large, flat field. In a series of 5- and 10-minute trials, participants walked in circles that often were no more than 20 meters wide. Only three veered consistently to the right or left.
When wearing shoes with soles that differed in thickness, artificially making one leg longer than the other, students exhibited similar circular walking patterns.
Souman now plans to study people walking on a special treadmill through a virtual forest, where he can control whether walkers see just the ground or other visual cues.
In emergency situations, cinematic monster hunters and others may become so panicked that they disregard external heading cues and unintentionally end up back where they started, Souman suggests.