You'd probably like to think you're blessed with an accurate "position sense" - that if you were to close your eyes, you'd nonetheless know where you are in space and in relation to other objects. But without the help of vision you're likely to overestimate your girth and underestimate your length, at least when it comes to your hands, according to a study (abstract) just published in Proceedings of the National Academy of Sciences.
Researchers at the Institute of Cognitive Neuroscience at University College London created an experiment in which the hands of study subjects were hidden from view. The subjects were then asked to guess the position of their unseen knuckles and fingertips and erred consistently on the side of stubby. They guessed on average that their hands were about 28 percent shorter and 69 percent wider than they actually were.
That doesn't mean healthy people don't know what they look like, says author Matthew Longo, but:
[He] speculated that these disproportions might occur in other parts of the body as well. "These findings may well be relevant to psychiatric conditions involving body image such as anorexia nervosa, as there may be a general bias toward perceiving the body to be wider than it is," Longo said. "Our healthy participants had a basically accurate visual image of their own body, but the brain's model of the hand underling position sense was highly distorted. This distorted perception could come to dominate in some people, leading to distortions of body image."