Helmet-mounted displays (HMDs) are being increasingly used by the military outside of the traditional cockpit
environment. In these applications, attention, functional field of view (FOV), and mental workload are important human
factors issues. While some research has begun to address these issues, not many have considered how alternative
placements of the monocular eyepieces in the visual field effects performance. We investigated task performance using a
monocular HMD that was adjustable so that it could be placed within or outside of the FOV of the user. There were three
parts to the experiment. In the first part, observers performed a visual search task to serve as a baseline measure of
performance. In the second part observers wore the HMD in one of two positions and again performed the search task.
Finally in the third part, observers completed the search task while performing a reaction time task that was displayed on
the HMD (again placed in the two positions). Results of task performance are discussed in terms of the functional FOV,
attentional demands on the user, and differences between tasks to be performed on an HMD. Recommendations are
given for design, use, and future research on HMDs.