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Tuesday, April 1, 2008

Do our feet deceive us more than our eyes do?

Researchers have known for some time that people are surprisingly accurate at visually judging distances to objects as far as 25 meters away. If you're allowed to briefly look at an object up to that distance away, then blindfolded, you'll walk right up to it with great precision. If you walk halfway, you can throw a ball the remaining distance, again, quite accurately.

But in 2000 Marla Bigel and Colin Ellard attempted a simple replication of the study: instead of viewing the object, volunteers were led blindfolded to the object and back, and asked to walk back to the object again. Now, instead of accurately walking the distance, they systematically overestimated the distance to the object. Could our feet deceive us more than our eyes, even when we're simply asked to retrace a path we've just taken?

There's another possible explanation: maybe being led is what causes the deception. In a new study, Ellard and Sarah Shaughnessy asked 30 volunteers to walk blindfolded along a roped-off 10-meter pathway. They could use the ropes to guide themselves, but were never led by researchers. As before, they walked the distance to the object, then returned to the starting point, and finally attempted to walk the same distance again. Another group of volunteers simply looked at the object and then tried to walk to it blindfolded. Here are the results.


Now everyone was very accurate at pacing off the distance, whether they had walked it off or viewed the target first. It appears that the act of leading a person blindfolded over a distance systematically skews their perception of the distance, but when they walk unassisted, people are able to accurately judge distances, even while blindfolded.

So if both viewing the object and walking to an object result in accurate distance estimates, then which method takes precedence? In a new experiment, Ellard and Shaughnessy had volunteers both walk to the object and view it -- but the object was a different distance from the viewer each time. So the object might have been 6 meters away when the distance was walked, but then it would be viewed 8 meters away. As you might expect, responses were biased towards the most recent distance, whether the object was viewed or walked to. But responses were biased more to the viewed object. When the viewed object was seen last and 8 meters away, viewers were just as accurate as when they had only seen the object at that distance.

So humans appear to be more comfortable using the visual system to judge distance than using the motion of their bodies. Researchers had initially found that that people were very bad at judging distances when blindfolded, but then realized that people were preoccupied with worries about whether they'd bump into a wall -- so all the experiments discussed here were conducted outside, in an open field.

Original here

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