There are many potential uses of helmet-mounted displays (HMDs). One is to allow aircrew to spend increased time off- boresight scanning the outside world for threats or targets. Another is for acquiring a target and subsequently employing a weapon whilst looking off-boresight. An experiment was conducted to examine the use of HMDs for both these tasks using four different attitude displays: pitch ladder, cylinder, arc segmented attitude reference and roll-pitch. The task involved subjects flying a simulated low-level, high-speed mission which was divided into two phases. Phase one required subjects to scan off-boresight for air threats and acquire them by using the off-boresight capability of the HMD. Phase two required subjects to use the head-down display (HDD) to locate ground targets and use the HMD off- boresight capability to acquire them. Novel objective performance measures, designed specifically to evaluate HMD symbology, were collected. Overall, it was found that performance was superior when using the pitch ladder than other displays. This was supported by the subjective findings that it provided higher situational awareness than other displays. It was concluded that the advantage for the pitch ladder may have been due to having the same symbology on the HUD and HMD, enhancing smooth transitioning between the two displays. The importance of developing operationally relevant tasks and measures for the evaluation of HMDs are discussed and the implications of this research for future work are considered.
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