Can blind people, or blind-folded people, walk in a straight line?
We put this to Jan Souman, formerly of the Max Planck Institute for Biological Cybernetics in Tubingen, Germany...
Jan - It is a very interesting question. I guess most people intuitively would say that blind people will be better at walking a straight line than sighted people when blindfolded; Because of course, blind people have been used to not seeing all their life and therefore probably developed some strategies of coping with that handicap. It actually turns out that blind people are not better at that than sighted people.
So people have done two kinds of studies, one kind of study is just exactly that test - just to have people walk in a straight line while either blindfolded or being blind and see how well they do and it turns out that blind people do not do better than sighted people who are blindfolded. And the other test that has been done is have people walk in a curved path by holding on to something that guides them on this curved path and then have people judge whether they're curving to the left or to the right.
Again, it turns out that blind people are not better at that than sighted people who are blindfolded. The problem for blind people is so big that sometimes it happens that when blind people try to cross a wide street or multiple lane street, that they end up at the same side of the street where they started from. So they actually walk half a circle while trying to cross the street.
Itís actually not that surprising if you think about it, that blind people are not better at walking a straight line than sighted people because the brain of people trying to walk in a straight path while blindfolded are blind only has internal information, only information that comes from the body itself, from the sense of balance, the vestibular organ, from the muscles and the tendons in the body and so on. And all those cues only gives information about the relative changes in walking directions. So with every step, it basically tells the brain whether itís still going in the same direction or veering a little bit.
Diana - So why might this be?
Jan - Because the signals are noisy signals, they're biological signals so there are some kind of noise in those signals. There will be small errors in those signals and those add up over time and therefore, you end up walking in circles because that's just the accumulation of errors over time. That works the same way for blind people as for sighted people who are blindfolded. So that might be a possible explanation of why people walk in circles when they get lost or when walking blindfolded, also why blind people are not better at it than blindfolded people.
According to this 2009 paper sighted people can't walk in a straight line without a reference like sun/moon/landmark, and the blindfolded walk in even smaller circles than the sighted.
All people have a dominant side, in other words, your right hand side is stronger than your left.
In the paper cited by RD above, they control for that - even to the extent of x-raying a subject's legs to prove that there is no length-disparity and also artificially lengthening a leg by building up a shoe (without the wearer be aware); in this latter case, no bias was introduced in terms of favoured side.
Balance, is the result of a number of body systems working together. Specifically, in order to achieve balance the eyes (visual system), ears (vestibular system) and the body's sense of where it is in space (proprioception) ideally need to be intact.