MULTIPLE IMAGES APPEAR WHEN MOTION ENERGY DETECTION FAILS

Under certain conditions, multiple images trail behind a target moving across a cathode ray oscilloscope. Given the relatively sluggish temp oral response of the visual system, it is surprising that when an imag e is rapidly displaced, multiple images are not seen under most circum stances. The authors have explored the conditions under which multiple images appear. The velocity at which multiple images first appear (al iasing velocity) was recorded across a range of image update rates for a drifting bar and for band-pass and low-pass filtered bars. Multiple images were found to appear when a fixed spatial displacement was exc eeded between image updates. The value of this displacement was approx imately invariant with drift speed. The effects on aliasing velocity o f band-pass and low-pass filtering are similar to those reported for m otion detection after comparable manipulations of a random dot kine-ma togram (R. Cleary and O. J. Braddick, 1990a, 1990b). The findings sugg est that multiple imaging occurs when motion energy detection fails.