HELMET-MOUNTED DISPLAY ATTITUDE SYMBOLOGY - AN EVALUATION OF COMPRESSION RATIO

This study addressed the development and evaluation of empirically-based helmet-mounted display (HMD) symbology sets. Three attitude formats and three altitude formats were evaluated within a composite tactical aircraft symbology layout. The attitude formats varied in basic shape and symbol compression ratio (SCR = ratio of the angle represented by the symbol to the symbol's subtended visual angle). Symbols which incorporate high SCR represent large angles and have a slow rate-of-motion relative to uncompressed formats. The altitude symbologies were formed of vertical scale and dial formats and included vertical velocity indicators. Subjects performed a flight-path maintenance task within sessions of differing ''real'' horizon presence and orientation. The formats were evaluated under a task which was designed to require both gross and precise responses. The results showed that performance was influenced by the manipulation of the attitude symbology formats, and suggest that symbol compression may be advantageous. Transparent displays are advantageous in environments and processes where reference information is required during visual control tasks. Symbol compression may influence information interpretability in head-coupled displays where reference symbols are disassociated from velocity vector. These symbology features should be addressed when considering the application of head-coupled displays.