Hearing thresholds during Gz acceleration with masking noise

Future fighter aircraft will include three-dimensional sound signals as part of the human-machine interface. The reduction in cerebral vascular flow associated with maneuvering acceleration (+Gz) may affect a pilot's ability to perceive and interpret such aural cues. We hypothesized that vascular deprivation along the cochlea produced by +Gz would raise hearing thresholds either globally or specifically at 1000 Hz. We compared hearing thresholds for pure tones at 250, 1000, 6000 and 10,000 Hz during exposure to +1 Gz vs. +4 Gz. Experiments were conducted with steady noise input to the earphones to mask centrifuge noise. Paradoxically the hearing threshold was slightly yet significantly reduced for 1000 Hz (53 dB at 1 G vs. 47 dB at 4 G) while remaining unchanged at other frequencies. Audition did not change at +4 Gz, contradicting our hypothesis. We infer that the change at 1000 Hz is not a central effect, but instead represents a disturbance of middle ear transmission mechanisms. The absence of any general hearing loss at +4 Gz favors the possibility of using complex sounds such as three-dimensional sound in aeronautical human-machine interfaces during acceleration.