Effects of Age on the Judged Distance to Virtual Objects in the near Visual Field

The following experiment examines effects of observers' age on their judged depth of nearby virtual objects displayed with see-through, Helmet Mounted Displays (HMDs). Monocular, biocular or stereoscopic viewing conditions were used. Two previous finding were investigated: 1) the effect of accommodative demand on judged target depth (Ellis & Menges, 1995) and 2) the change in judged depth of a virtual object due to the introduction of a physical surface at its previously judged depth (Ellis, Bucher & Menges, 1995). Observed effects were consistent with the older subjects' loss of accommodative response and reflexive accommodative vergence. In the present study it was found that only subjects younger than 38 yrs were able to benefit from correctly presented accommodative demand in the monocular viewing situations. Older subjects were especially likely to make greater depth judgment errors in the monocular viewing situations and would especially benefit from compensatory design of the stimulus to correct their larger judgment errors. Biocular and stereo viewing conditions were approximately equivalent with respect to observed judgment bias and produced roughly comparable accuracy for young and old subjects.