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NO MATTER how bad you think you are at maths, your brain is a whiz when it
comes to trigonometry.

To help figure out how far away an object is, people unconsciously measure
the angle between two lines of sight鈥攖he horizontal plane and the line to
the base of that object鈥攔esearchers in Tennessee have found. Once the
brain estimates this angle, it can then calculate its distance with amazing
accuracy using the trigonometric tangent function.

鈥淧revious studies could not conclusively prove it,鈥� says Teng Ooi at the
Southern College of Optometry in Memphis, Tennessee, because they could not find
a way to exclude the effects of other distance clues that the visual system also
rely on, such as size.

To get round this, Ooi and her team fitted volunteers with prisms worn in
front of the eyes. The prisms allowed the researchers to shift the angle objects
appeared to be up or down, without changing their size or any other aspects of
the visual scene.

When the volunteers viewed objects through prisms that increased the
perceived angle, Ooi found that they underestimated the distance of objects. But
the subjects鈥� brains quickly adapted to this change, and when the prisms were
removed they overestimated distances for a while instead.

This ability helps to explain how our brains can judge distances using
limited visual cues from just one eye, says Ooi. It could also be useful for
designers who are trying to develop more realistic computer graphics and virtual
reality systems.