Effect of "inside-out" and "outside-in" attitude displays on off-axis tracking in pilots and nonpilots

Pilots employing helmet-mounted displays spend sustained periods of time looking off-axis, necessitating the inclusion of attitude symbology on the helmet to maintain spatial awareness. We examined how fundamentally different attitude references, a moving-horizon ("inside-out") or a moving-aircraft ("outside-in"), affected pilot and nonpilot attitude control when looking on- or off-axis. Both a rear-view and a side-view outside-in perspective were depicted to investigate the effect of control-display compatibility.

Subjects performed a compensatory pitch-roll tracking task either looking on-axis or 90 degrees off-axis using three symbologies: 1) a compressed pitch ladder with horizon line; 2) a 3-D aircraft representation viewed from the rear; and 3) a 3-D aircraft representation viewed from the side. Tracking error in roll and pitch, control bias, and subjective ratings were collected and analyzed.

There was no significant difference in the tracking performance of U.S. Air Force pilots in pitch and roll using the inside-out or outside-in rear-view formats on- and off-axis, although they preferred the inside-out format. Nonpilots tracked significantly better using the outside-in rear-view format, which they also preferred. Both groups tracked poorly using the outside-in side-view format and control-display compatibility had no important effect.

Pilots are equally adept using outside-in and inside-out displays. Given that an outside-in display may better reflect a person's inherent frame of reference for orientation (as evidenced by the nonpilots' superior performance with it), the results seem to indicate that pilots, through experience, have adapted to an inside-out frame of reference.