A Comparison of Two Subject-Controlled Attitude Measures during Somatogravic Illusion Exposure

The United States Air Force School of Aerospace Medicine USAFSAM has a requirement for a performance evaluation and comparison of two subject-controlled attitude indicators during exposure to the somatogravic or posturogravic illusion. This illusion is well known for giving aircraft pilots a false sensation of excessive pitch-up during take-off. With a lack of visual stimuli, the pilot misinterprets the resultant gravitoinertial force vector as approximating the vertical force vector of gravity. Accidents occur when pilots adjust to what they feel is level flight, when they are, in fact, pitched down toward the ground. The USAFSAM Vertifuge spatial disorientation device was used to generate this illusion in 16 subjects 8 experienced pilots and 8 nonpilots by varying gravitoinertial and actual cabin pitch positions. Each subject rode the Vertifuge twice. During one session, the subject used a canopy-mounted downpointer to estimate position in space relative to the ground, and in other session the subject used a joystick-controlled inside-out aircraft attitude indicator. As expected, the results clearly indicate that the canopy-mounted downpointer is better at quantifying the somatogravic illusion in this Vertifuge study. Furthermore, it is apparent that there are no significant differences in performance between pilots and nonpilots using either device.