Walking In A Straight Line

Walking in a straight line, how difficult can it be? Well it can be really difficult walking in straight line if we are asked to do so in an unfamiliar terrain such as a jungle/desert. Even if the terrain is familiar but if we are blindfolded it’s really impossible for us to walk in a straight line, instead we tend to walk in circles or loops and this phenomena of walking in circles has been a puzzle for humans. The idea of walking in circles when lost in forest or desert have been there in the popular culture since a long time [Mark Twain in Roughing it ,1872; The Lord of the Rings, 1954; The Blair Witch Project, 1999 etc.] but no detailed scientific study has been conducted to understand it. That was until 2009, when Souman and group from Max Planck Institute of Biological Cybernetics in Germany decided to do some experiments to understand this mystery [published in Current Biology, 2009]. There have been several hypotheses as to why we tend to walk in circles instead of straight line. Two main hypotheses include 1)  hemispherical asymmetries in our brain can result in different amount of dopamine being released resulting in turning in a particular direction (directional bias), or 2) maybe different physical attributes or bio-mechanical asymmetries, such as difference in size or strength of left or right legs can add to a certan bias and lead us in a circle instead of straight line.

Soulman tested both the hypotheses and found no correlation. Subjects walked randomly towards left or right  but in a circle irrespective of their directional biases, showing that there was no constant bias favoring turning in a particular direction. For testing the second hypothesis of biomechanical assymetry, they glued additional soul in one of the boots, resulting in extra length of one of the legs but the result showed no correlation.

The subjects in this study were asked to walk in a straight line in a vast open forest and Sahara desert without any blindfolds. In one case the day was cloudy while in the other case it was sunny. the result was that on the cloudy day, the subjects started walking in a loop after travelling certain distance, even criss-crossing their earlier paths even without noticing it while on the sunny day, subjects did fairly well walking in a straight line. In the image below, the red dots mark the starting point of the walking tracks, the colored lines show the actual ways that the test persons covered. The test persons PS, KS and RF could not use the sun for orientation, whereas the sun started shining just after SM started his trial. [Source: Jan Souman,tuebingen.mpg.de]

In second set of experiements, the researchers blindfolded the subjects and asked them to walk in a straight line, and ofcourse they failed. Interestingly, they walked in very tight loop of diamter smaller than 20 m and while doing this, the subjects always perceived that they were walking in a straight line.

Possible explanations can be that when walking in an unfamiliar terrain without proper external cues (such as sun) or walking blindfolded, we introduce small random errors in what we pereceive as “straight ahead”. These random errors keep on accumulating on our subjective perception of ” straight ahead” ultimately leading us to drift in different direction as compared to “true straight ahead”. If these accumulated random noises are small, we tend to walk in straight line, but if they grow large, we tend to move in circles or loops. Lack of proper external cues such as no sun, or lack of distinguishing trees in the forest, or distinctive landmarks in desert, or lack of any sort of visual cues when blindfolded can result into large accumulation of random errors. These random errors can possibly affect our Vestibular system comprised of inner parts of  ears and brain which can in turn affect our sensorimotor system. Panic or emergency situations (lost in forest) can cause individuals or groups to ignore even distinctive landmarks and can lead them to walk in circles.

Now you can go and try for yourself if you can walk in a straight line in an open parking lot or park if you are blindfolded and what’s the longest distance you wan walk in straight line before you start walking in a loop!

Image credit: First image- Flickr user Bods; Second image: Max Planck Institute for Biological Cybernetics

Article: Walking Straight into Circles, J. Souman et al. Current Biology, doi:10.1016/j.cub.2009.07.053

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