Rotating Trapezia Which Appear Luminous and Transparent during Reversals

Abstract

If a rotating trapezium is lit by a visible source at one side, it sometimes reflects light to the observer and sometimes appears dark. This provides information about its orientation which is relevant to the suppression of apparent reversals. Marked suppression does occur if the light is between the observer and the object, but in other cases novel phenomena arise. The onset of light may precipitate corrections, ie discontinuous shifts from an illusory percept to a veridical one. At certain stages the object may also appear to be transparent and luminous, particularly if a bar has been passed through it: the bar then appears to be visible through the object. The effects illustrate the limited use vision makes of seemingly excellent sources of information, but they also indicate that the problem may lie in misplaced sophistication rather than crudity.