WHAT PRODUCES SHRINKAGE OF APPARENT SIZE FOR A MOVING OBJECT

An object moving in the frontal plane is perceived to shrink to a frac tion of its stationary size, and the greater the velocity of the objec t, the greater the shrinkage of apparent size. This fact has been expl ained either by the shrinkage of effective retinal size of light emitt ed by the moving object or by the subjective Lorentz contraction in wh ich apparent size of an object is assumed to diminish as the apparent velocity increases. To examine the validity of these theories, the 13 subjects made size- and velocity-matches for a moving target under eac h of 16 combinations of angular velocity, gaze state, and visual field . The greatest shrinkage of size was obtained for the object moving sw iftly across a narrow visual field while the eyes gazed a stationary p oint, and the velocity matches were related to both angular velocity a nd gaze state but were not related to apparent size. All aspects of th e results did not agree with the previous theories. Instead, effective duration for which the retinal image is formed at the fovea is shown to be critical for apparent size of the moving object.