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 accommodation response of processing information presented either visually or aurally while viewing a real-world scene. A number of different conditions were tested in which a mental processing task, a virtual image overlaying the real world (as is the case with head-up displays), or both were present. These manipulations provided two factors that have previously been demonstrated to have some influence on the accommodation response: mental effort and perceived distance. They also allowed the investigation of the influence of the source modality of the information to be processed. The results suggested that these influences may have a cumulative effect on the visual accommodation response, possibly mediated by attentional factors.