Studies in perception At arm’s length: Plasticity of depth judgment

Arm’s length: a relative measure

People judge depth most accurately at a distance that corresponds with their arm length (green triangle). Too close and they overestimate depth (yellow); too far leads and they underestimate (blue). If they perceive their arm to be longer, researchers found, the whole continuum shifts farther away. Credit: Istituto Italiano di Techologia

People have a distance at which they are best able to judge depth. That distance, it turns out, is dictated by how long people understand their arms to be. Researchers showed this in the Journal of Neuroscience by tricking subjects with virtual reality into thinking their reach was longer than it really was. The result? Their accurate perception of depth via sight moved outward and touch became more sensitive.