In 2007, Jan Souman dropped three volunteers into the Sahara desert and watched as they walked for several miles, in an attempt to walk in a straight line. Souman was interested in the widespread belief that lost travelers end up walking in circles, a belief that has never been properly tested but has nonetheless become firmly entrenched in the popular consciousness. Just think about Frodo and Sam's hike through Mordor or the three hapless teens in the Blair Witch Project.
To see how non-fictional humans would fare, Souman tracked a group of volunteers using GPS as they walked through a thick German forest or a featureless Tunisian desert, as well as others who strolled through a large field blindfolded. The result: they did indeed go in circles but with no preference for any direction and only when they couldn't see or when the sun or moon weren't visible.
It seems that with some sort of reference point, we're entirely capable of walking in a straight line, even in a featureless desert where dunes obscure the horizon or a busy forest that's riddled with obstacles. The sun's good enough for these purposes, even though it's position changes as the hours pass. Without any such cues, we quickly veer off course.
The two volunteers who walked through in the forest on a sunny day managed to keep to a perfectly straight line, wandering only in the first fifteen minutes when the sun was behind a cloud. The four people who walked on much cloudier days all ambled in circles, repeatedly crossing their own path without knowing it. The desert walkers fared about as well - those who walked during the heat of the day veered slightly but kept reasonably straight. A third man walked at night; he too kept a direct course when the moon was visible but when it vanished behind clouds, a couple of sharp turns sent him back in the direction he came from.
Scientists have put forward many explanations for the circular rambles of lost walkers. Some say that most people have one leg that's longer or stronger than the other and over time, these differences add up to a curving course. Others say that asymmetries in our very brains set up a tendency to turn in one direction. Without a guiding light or landmark, these small biases would make their presence felt.
But Souman thinks otherwise. He set a group of 15 blindfolded people loose in a large field, told them to walk straight ahead and watched them for 50 minutes. All of them walked in very random paths, including large flamboyant loops and, on occasion, surprisingly small circles of as little as 20 metres in diameter (little enough to fit within a basketball court).
Only three of the 15 people consistently veered in one direction and they did indeed go round in circles; the others walked more chaotic paths. On the whole, their meanderings had no consistent bias and they would turn one way as often as the other. Indeed, one of the volunteers, known only as KS, took part in both experiments and while he had the strongest directional bias while blindfolded, he actually veered in the opposite direction in the forest.
That strongly argues against the influence of asymmetric legs or brains. Souman certainly ruled out the leg hypothesis by showing that the relative strengths of his walkers' legs didn't relate to the average direction of their turns. He even X-rayed the legs of one of his recruits to measure their length and then evened things up with shoes of varying soles. They made no difference to his path.
So without landmarks to guide them, the walkers were relying on feedback from their bodies (proprioception) and their sense of balance. These cues can help over short distances, but Souman says that they soon build up "sensory noise" that renders them inaccurate and causes the person's trajectory to drift both increasingly and randomly.
It's telling that the blindfolded walkers in the open field behaved in very similar ways to the ones in the cloudy forests - their jaunts included bouts of random direction interspersed with systematic circling. This may have been because of all sorts of obstacles or local landmarks in the forest, but not so in the field.
Instead, Souman suggests that people circle when their internal sense of "straight ahead" becomes corrupted by random errors in their sense of touch, balance or spatial awareness. Small errors lead to random walks, while larger errors cause circling. And that has a massive impact on their ability to get, well, anywhere.
Despite walking for 50 minutes, most of these people never made it very far. Within a few minutes, their average distance from the starting point levelled off so that they were usually around 100 metres of it. A visual cue, however, can do wonders for resetting our navigation. If Souman allowed his blindfolded bumblers to lift their blindfolds for a minute out of every five or ten, they managed to recalibrate their sense of "straight ahead" and started each block of time in a straight line again.
As Souman himself concludes, "Ironically, in the age of ubiquitous navigation systems in airplanes, cars, and even mobile phones, we are only beginning to understand how humans navigate through their environment, exploring uncharted terrain." His study shows that even the simple act of walking in a straight line is more complex than it might first appear.
Reference: Current Biology doi:10.1016/j.cub.2009.07.053 Can't find the paper? Be patient - most journals have a few hours' delay between the lifting of press embargoes and the publication of papers. For PNAS, this can be up to a week.
More on navigation:
A 6 kilometre trek on the back of a snail
Losing Nemo - acid oceans prevent baby clownfish from finding home
Bats: compasses, tongues and memories
How sharks, penguins and bacteria find food in the big, wide ocean
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Very interesting. Thanks for the post.
Do shoes vs. bare feet make a difference?
Speaking of fictional characters going in circles: I faintly remember one of the characters in the movie Flight of the Phoenix claiming that he could walk in a straight line across the desert due to his military training - because he was trained to march in a formation, his steps would be more even than a civilian's. Would be interesting to see if that advantage would really materialize in an experiment like this.
Were there any conditions where people's paths approximated a mathematical random walk? I get the impression they didn't, which would be an interesting observation in itself.
Would be interested if the statistics are in any way similar to a totally random walk, with uncorrelated steps and the distance from the origin goes as the square root of time. Presumably they would be if you could leave them for weeks and weeks - maybe not I don't know.
Will check the paper when the doi's working.
New theory: people aren't that bright.
If you happen to be navigating at night and can see only the Moon, you're in luck. From the Moon you can tell where the Sun is, and you know where the Earth is. Those three define a plane, and a perpendicular to that plane points somewhere near Polaris (or the Southern Cross) if you're into negative latitiudes.
I wonder if blind people do any better?
I started on your blog today and here I am again. Take that, data.
It's interesting that most people end up within 100 meters of where they started off. Maybe evolution has programmed us not to stray too far if we don't know where we're going. It's nature's way of keeping us in one spot when we're lost.
...sounds like the chaos game, I'd like to see it charted.
Harold Gatty in Nature is your Guide describes a technique for groups to travel in straight lines. The group walk in single-file with a reasonable distance between them. The person at the tail sights along the line and announces any tendency of the leader to drift right or left, using the line as a whole as a reference. He claims it was used by explorers in the Australian desert.
The random walks look a bit like "worm tracks" when C. elegans nematodes wander around on an agar plate. There are mathematical tools for analyzing these paths, so maybe researchers could learn more about random human walks that way.
http://www.ncbi.nlm.nih.gov/sites/entrez?db=pubmed&cmd=retrieve&dopt=Ab…
http://www.ncbi.nlm.nih.gov/sites/entrez?db=pubmed&cmd=retrieve&dopt=Ab…
My takeaway: hunker down in a blizzard, 'cause you ain't goin' nowhere.
The only straight line a person can walk IS a circle.
Earth is a spheroid, people.
Those that *seem* to walk in a straight line are simply walking bigger circles than those that immediately start curving to the right or left.
Kindergarten stuff!
I moved from the northern hemisphere to the southern at the start of the decade. When I first got here, and maybe for the first six months or a year, I got lost in the city often, more confusingly than I would have expected from having been around strange cities before. Usually on long walks, but occasionally over short distances with frequent stops.
I was a little perplexed. I wasn't used to taking a long stroll and ending up at right angles to my intended route after a couple of hours. I was used to looking at a map before leaving home, then confidently striking out in the right direction and eventually hitting my target, not a suburb in a completely different part of the city. It was like I'd developed a tendency to turn hard left, for some reason.
Then one day I realised: I may have been unconsciously using the sun to orient myself all along, but I was now in the southern hemisphere, with the sun traversing the sky in the opposite direction.
I don't get lost much any more, but If I go back to the UK, I expect I might start turning hard right for no obvious reason.
Anecdotal, but I think it's an interesting hypothesis for why I was so lost. Then again, the pubs here in Sydney are *very* good...
Jon beat me to it. I was wondering about the blind myself. There is almost always some background noise from birds and insects and traffic. Wouldn't help much in a forest, but in an open field one might hear a stand of trees getting closer or notice the sound "shadow" of a large boulder. Just moving around my house in the dark or w. my eyes shut I notice changes in the background noise (even that which is now reduced simply to noise) as I near walls and doorways.
Worth pointing out that the navigation abilites of blind people are even better than previously thought: http://scienceblogs.com/notrocketscience/2008/12/blind_man_navigates_ob…
I question the validity of the findings for the blindfold test. The tight circles make a lot of sense. No matter how big of an open field I see in front of me prior to being blindfolded, after a few steps I'm going to hesitate. The circles could indicate that most people have a very poor sense of how far they have walked when blindfolded.
I recall a teamwork exercise where I was blindfolded and walked a path guided by a partner who gently held me elbow. Even though I could heard the ocean and knew we were on a wide beach, a relatively short walk seemed unending.
So if you put people in a wide open field, then blindfold them, they will soon, and far short of the actual limits of the field, feel that they have walked to the border of the field and that they better turn or risk walking into some unknown danger.
I'm a big science geek but I like aerodynamics and I'm a mechanic, but I'll be respectful and say very good. Though as someone stated earlier, earth is a spheroid and to them I say don't forget that it's terrains varies, geologically speaking, it has a variety of terrains from domed, arched, flat, etc. Remember we learn our shaped before we even enter school. So if your gonna try to act all high and mighty DDeden because you know something doesn't mean you should try to put down others work and or findings, man your the type that lose teeth to guys like me. Respect people findings okay.Let try to keep it real and if you have something to say or add don't try to be so insulting. I know I just had to say the teeth thing it's a fact. Thanks again Ed Yong very interesting.
People in northern hemisphere tend to walk to the right because of the rotation of the earth. same as weather high pressure . But all people may not follow this pattern because of human free will. Toilet's go to the left.