Distance perception of stereoscopically presented virtual objects optically superimposed on physical objects by a head-mounted see-through display

The influence of physically presented background stimuli on distance judgements to optically over-laid, stereoscopic virtual images has been studied using head-mounted stereoscopic, virtual image displays. Positioning of an opaque physical object either at the perceived depth of the virtual image or a t a position substantially in front of it, has been observed to cause the virtual image to apparently move closer to the observer. In the case of physical objects positioned substantially in front of the vir-tual image, subjects often perceive the opaque object as transparent. Evidence is presented that the apparent change of position caused by interposition o € the physical object is not influenced by the strengthening of occlusion cues but is influenced by motion of the physical objects which would attract the subjects ocular vergence. The observed effect appears to be associated with the relative conspicu-ousness of the overlaid virtual image and the background. This effect may be related to Foley's mod-els of open-loop stereoscopic pointing errors which attributed the stereoscopic distance errors to mis-judgment of a reference point for interpretation of retinal disparities. Some implications for the de-sign of see-through displays for manufaduring will also be discussed briefly