Why lost humans walk in circles

IT'S a staple of adventure stories: the hero, lost in the wilderness, painstakingly tries to find his way back to civilisation only to stumble across his own tracks and discover that he has been walking in circles.
Now the popular belief that people in unfamiliar surroundings tend to walk round in circles has been confirmed by scientists.

Experiments in a German forest and the Sahara desert in Tunisia have shown that lost people double back on themselves unless they have a marker, such as the Sun or Moon, to guide their way.

"The stories about people who end up walking in circles when lost are true," said Jan Souman, of the Max Planck Institute for Biological Cybernetics, in Tubingen, who led the research.

"People cannot walk in a straight line if they do not have absolute references, such as a tower or a mountain in the distance, or the Sun or Moon, and often end up walking in circles."

The scientists, whose work is published in Current Biology, also debunked a popular explanation of walking in circles.

It has been suggested that people might veer in one direction because one leg is slightly longer or stronger than the other. Over time such small differences could cause somebody to walk in a circle.

The new research, however, in which people were blindfolded and asked to walk in a straight line, found that while they ultimately walked in circles, they did not do so reliably in any particular direction. The subjects sometimes veered left and sometimes right, which would not happen were differential stride length or power a factor.

Dr Souman said that it was more likely that circular walking patterns tended to emerge from increasing uncertainty about direction. "Small random errors in the various sensory signals that provide information about walking direction add up over time, making what a person perceives to be straight ahead drift away from the true straight ahead direction," he said.

In the study the research team took six volunteers to the Bienwald forest, in southern Germany, and asked them to walk in as straight a line as they could while their progress was monitored using GPS devices. Four volunteers walked on a cloudy day when the Sun was hidden and two in bright sunshine.

The four who walked under clouds all moved in circles and three of them crossed their own paths repeatedly without noticing. The two volunteers who were able to see the Sun walked in straight lines, except for 15 minutes when it was obscured by cloud.

A similar pattern occurred when three other volunteers were tested in the Sahara, in southern Tunisia. Two volunteers who walked during the day and could see the Sun veered off course but did not walk in circles. The third, who walked at night, kept to a straight line when the Moon was visible but doubled back on himself when it disappeared behind clouds.

Marc Ernst, another member of the study team, said: "The results from these experiments show that even though people may be convinced that they are walking in a straight line, their perception is not always reliable. Additional, more cognitive strategies are necessary to really walk in a straight line."

The team is planning to investigate the phenomenon further in the laboratory by asking volunteers to walk through a virtual reality forest on a specially designed treadmill.