Apparent Motion in Geometric Depth

The ability to detect small excursions of apparent movement of a point light source was investigated. Apparent movement was achieved by alternately presenting a point source in two different planes. The presentations, each lasting about 500 milliseconds, had an overlap of approximately 8 milliseconds. Using 7 subjects, the limen for apparent motion was a stimulus separation of 43.9 mm, which is a visual angle of 1′ 21″. Possible application of the effect in a highly precise visual guidance system is discussed in light of the results.