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Viewing difficulties with head-mounted aids for mechanical assembly using nearby virtual objects

A head-mounted electronic haploscope was used in a see-through format to present computer generated, space-stabilized, nearby wire-like virtual objects to 18 subjects. The visual requirements of this task are very similar to those needed for use of a similar head-mounted information display under study as a primary information aid for manual aircraft wire harness assembly. The subjects visually traced the snake-like and rectilinear wire paths with a visual cursor before their dominant eye. Three subject groups used either monocular, biocular, or stereoscopic display conditions for 30 minutes of tracing. Pre and post tracing subjective viewing difficulties, disorientation, nausea, and measures of stereoscopic threshold, near and far horizontal and vertical phoria were made. Only the viewing difficulty, i.e. the eye and head/neck aches score, changed significantly. Biocular conditions were worse than either monocular or stereo which were nearly equivalent for this measure. The biocular viewing difficulties are likely due to conflicting looming and stereo disparity cues to vergence. Accordingly, special geometric design enhancements probably will be needed for biocular displays for work within arms reach.