Visually Perceiving What is Reachable

Four experiments designed to assess observers' ability to perceive whether or not something is within reach, under a variety of circumstances, are reported. Actual reaching ability is influenced by the posture in which reaching is to be done (e.g., with the arm alone, extending the arm while bending from the hip, and main- taining balance while bending from an upright standing position) and by the surface layout that confronts the reacher (e.g., the height of a surface to be reached and the presence of barriers to bending). Our investigation reveals that perceivers are sensitive to these influences on their reaching ability, although some are quite complex biomechanically. The results are discussed in the context of the demands that they place on computational and ecological accounts of perceiving what is within reach.