The effect of head tilt on perception of self-orientation while in a greater than one G environment.

The effect of head tilt on the perception of self-orientation while in a greater than one G environment was studied in nine subjects using the Armstrong Laboratory Dynamic Environment Simulator. After a 12-s stabilization period at a constant head tilt and G level, subjects reported their perception of the horizon by placing their right hand in a position they believed to be horizontal. Head tilt conditions ranged from -30 degrees to +45 degrees pitch over each of three head yaw positions. G levels ranged from one to four and were in the longitudinal axis of the body (Gz). Hand position was recorded in both the pitch and roll body axes. A function of head tilt did improve the fit of a multiple regression model to the collected data in both the pitch and roll axes (P < .05). The best fit was accomplished with a nonlinear function of G and head pitch. When the head remained level but the environment tilted with respect to the G vector (at angles similar to those perceived during head tilt), subjects accurately reported the environmental tilt. Head tilt under G can result in vestibular-based illusionary perception of environmental tilt. Actual environmental tilt is accurately perceived due to added channels of haptic information.