In one experiment objects with varying complexity were used as stimuli. On each trial an object or a distorted version is shown at an arbitrary orientation. The subject’s task is to decide whether the object is distorted or not, under several viewing conditions (monocular/binocular, with/without motion parallax, and near/far). The subject’s performance is measured by the detectability d', a conventional dependent variable in signal detection experiments. Highest d’ values were measured for the 3D display when the subject is allowed to walk around the display.

In a second experiment we tested the perception of 3D surfaces that have been rendered by a set of lines drawn on the surface. Each surface is rendered as a family of curves which are in the simplest case the intersections with a family of parallel planes. On each trial, a surface or its "distorted" version is shown in this way, in an arbitrary orientation on an LCD screen or in a volumetric 3D display. The subject’s task is to decide whether two sequentially presented surfaces are identical or not. The work investigates the question whether a surface rendered with planar and geodesic curves is easier to recognize than one where the curves are not planar or not geodesic. Our results show that the effect of the type of the contour is very similar in both monoscopic and stereoscopic viewing, but with a substantially higher performance in the stereoscopic case.