Does size matter?

For isolated objects in complete darkness, retinal image size contributes to distance judgments even if the true object size is unknown. Here we show that the same is true under more natural conditions. On a wide beach we positioned a red cube at 10-20 m distance and then asked subjects to walk to it while blindfolded. Subjects never had a close view of the cube and were unaware that on separate trials cubes with sides of 15 cm and 20 cm were positioned at the same locations. On average, subjects walked 1 m further after seeing the 15 cm cube than after seeing the 20 cm cube.