VISUAL ACCOMMODATION AND VIRTUAL IMAGES - DO ATTENTIONAL FACTORS MEDIATE THE INTERACTING EFFECTS OF PERCEIVED DISTANCE, MENTAL WORKLOAD, AND STIMULUS-PRESENTATION MODALITY

A study was conducted to examine the effect on the visual accommodatio n response of processing information presented either visually or aura lly while viewing a real-world scene. A number of different conditions were tested in which a mental processing task, a virtual image overla ying the real world (as is the case with head-up displays), or both we re present. These manipulations provided two factors that have previou sly been demonstrated to have some influence on the accommodation resp onse: mental effort and perceived distance. They also allowed the inve stigation of the influence of the source modality of the information t o be processed. The results suggested that these influences may have a cumulative effect on the visual accommodation response, possibly medi ated by attentional factors.