VISUAL ACCOMMODATION PROBLEMS WITH HEAD-UP AND HELMET-MOUNTED DISPLAYS

Virtual-image displays are likely to become more prominent in the airc raft cockpit, the most common examples being the head-up display (HUD) and, more recently, the helmet-mounted display (HMD). There is, howev er, a possibility that when using such a display the eyes may be inapp ropriately accommodated (focused). A series of experiments have been c onducted in which accommodation responses were measured to a virtual-i mage display presented either in darkness or superimposed on a 'real' scene. The results suggested that a number of people may focus inappro priately on displays of this sort, and that the problem is more pronou nced if the user has to mentally process the virtual image. The conseq uences of such misaccommodation are potentially very serious, includin g misperceptions of the size and distance of objects in the 'real' wor ld and a loss of contrast sensitivity, perhaps resulting in low contra st targets being missed.