Video: Walking in circles

Walking in circles (Image: Jan Souman/Max Planck Institute for Biological Cybernetics ) The trajectories of four participants during the forest experiment. Three of the participants walked in cloudy weather; their paths are highlighted in blue. The sun was out for one participant, whose path is shown in yellow (Image: GeoContent/ESA/Tele Atlas) A participant during the desert experiment. On this day the sun was visible and the subject was not blindfolded. He was able to walk in a reasonably straight line (Image: Jan Souman/Max Planck Institute for Biological Cybernetics) Because of the location work involved, the researchers could work with only a few participants. To overcome this, they have developed an omnidirectional treadmill that will allow participants to freely explore a virtual environment from within the controlled confines of the research institute (Image: Tina Weidgans/Max Planck Institute for Biological Cybernetics) Advertisement

If we can’t see landmarks, we really do end up walking in circles. That’s the conclusion of researchers who have tracked people trying to cross pathless deserts and forests.

Jan Souman of the Max Planck Institute for Biological Cybernetics in Tübingen, Germany, spends his days researching how the human brain combines information from the senses to build up a picture of the world around it.

When he was approached by a German television station that wanted to track people lost in the Sahara desert for a programme about human navigation, he thought the idea was pretty cool. Together they set about investigating the popular belief that people who are lost often find themselves walking in circles.

Souman and his team took volunteers into a forest and the Sahara, fitted them with a GPS tracker and asked them to walk on a straight course through the unfamiliar terrain. When the sun was out participants managed this surprisingly well, but on cloudy days or at night, with no visual cues to guide them, they veered away, often walking in circles.

“I didn’t believe that people really would walk in circles, so I was quite surprised,” says Souman.

Legging it

This is the first research to investigate whether lost people do unknowingly walk in circles. Several explanations for the idea have been suggested in the past, however, including physical differences between one side of the body and the other.

Souman’s team investigated this idea in a second experiment. Participants had their leg strengths measured or had the sole of one shoe made thicker to reproduce the effect of unequal leg lengths. They were then blindfolded and asked to walk a straight line in a large, disused airfield.

By depriving people of sight the researchers hoped that any inclination to move to one side or the other would be enhanced. But this didn’t happen: from test to test, most people changed the direction in which they strayed, showing that the human tendency to veer off course is not a result of physical asymmetry.

The paper proposes that the real reason for our inability to walk in a straight line without landmarks is likely to be accumulating errors in judging a straight path. Allen Cheung at the University of Queensland in Brisbane, Australia, who was not involved in the work, agrees: “Although each turn angle may be small and so go unnoticed, if it is not corrected, it will add up.”

Virtual stroll

Only a small number of people took part in the experiments, which limited their usefulness, but the team hope to overcome this soon. They have developed a treadmill that moves in all directions; when combined with a screen, it should allow participants to freely explore a virtual landscape. This will enable researchers to collect more results than was possible with the outdoor experiments.

“Another thing we found intriguing was that despite the sun moving in the sky throughout the experiment, when it was visible people walked in a remarkably straight line,” said Souman. “This suggests that they were effectively accounting for its movement.” Using their virtual set-up, Souman and his team would like to look into this further.

Journal reference: Current Biology, DOI: 10.1016/j.cub.2009.07.053