Abstract
Because of the inverse relationship between an object's distance and its retinal image size, visual judgments of size require information on distance. Holding an object can obviously influence where one considers it to be. Does kinesthetic information on the posture of one's arm influence visual judgments of the object's size?
Subjects were given a 5 cm cube at which they were asked to look before the experiment started, and to hold under the table in their left hand during the experiment. In their right hand, they held a rod behind a mirror. A simulated cube was presented binocularly—at the tip of the rod—via the mirror. Each presentation started with the subject placing the rod somewhere on a surface behind the mirror. The simulated cube appeared at that position (or 2.5 cm closer or further away) for 4 s, after which the subject had to indicate whether the cube he/she had seen was larger, the same, or smaller than the reference. The size of the simulated cube was varied between trials.
Whether the simulated cube was closer, at the same position, or further than the rod influenced the point of subjective equality (the size of the simulation at which subjects judged it to match the reference). However, the average distance between the subject and the simulation was also different. When the latter differences were taken into account (by selecting data with the same average distance between the subject and the simulation) the abovementioned influence of the distance between the rod and the simulated cube disappeared.
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