Why can't people go straight ahead

Science in dialogue

Why can't you walk straight ahead in the dark, but at some point go in circles?

It is unclear whether all people actually walk in circles in the dark. It is true, however, that in this case it is much more difficult to maintain a direction that has been taken.

This is - to a certain extent - due to the ability of humans to learn and the fact that they use several channels of perception to control their movement in space. On the one hand, this includes what is known as proprioception. That is the perception of the position of arms and legs in space. The brain receives information about this directly from the joints and muscles. The vestibular organ, part of the inner ear, is used to control balance. Seeing enables visual orientation in space.

It is only through the interaction of these three channels of perception that people perceive themselves and their actions in reality. How and with what weighting the individual channels contribute is not fixed once and for all, but can be adapted to the circumstances of the environment. In the case of people with visual defects, for example, the contribution of the visual channel will be less pronounced.

In general, however, vision plays a very important role in movement. People have learned to rely primarily on the visual perception of their surroundings. If you move in the dark or with your eyes closed, this channel of perception is lost and you have to orientate yourself exclusively on the basis of the other two - less practiced - channels of perception. Then it is difficult to keep going in the same direction.

The following experiment illustrates the importance of learning movement sequences: If you let people walk on a rotating disk and then ask them to walk straight ahead on “solid ground” with their eyes closed, they actually walk in circles. You learned this movement before. If they can then not use all the channels of perception available to them, they are no longer able to perform any other movement correctly.

The question was answered by Hans-Günther Nusseck, Max Planck Institute for Biological Cybernetics, Tübingen.