Stability and change in a perspective reversal illusion

A phenomenologieal explanation is presented for the stability and instability of the appearance of the form of objects as a consequence of changes in (1) the spatial position of the observer with respect to the object, and (2) the amount of time the object is observed from a specific spatial position. In support of the explanation, an object was constructed so that it would have multiple appearances when observed continuously from the same viewpoint. The initial appearance of this object when observed from different spatial positions and the constancy over time of these appearances were demonstrated to be in agreement with the theoretical expectations.