title: Hearing thresholds during Gz acceleration with masking noise.
abstract: BACKGROUND
  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.
  
  
  METHODS
  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.
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Département sciences cognitives, Institut de médecine aérospatiale du service de santé des armées (IMASSA), Brétigny sur Orge, France. pmb_sandor@imassa.fr
authors.forename: Patrick M B
authors.initials: PM
authors.lastname: Sandor
authors.forename: Lionel
authors.initials: L
authors.lastname: Pellieux
authors.forename: Martine
authors.initials: M
authors.lastname: Godfroy
authors.forename: Gérard
authors.initials: G
authors.lastname: Ossard
authors.forename: Armand
authors.initials: A
authors.lastname: Dancer
mesh_terms: D000054:Acceleration; D000328:Adult; D000337:Aerospace Medicine; D001301:Audiometry, Pure-Tone; D001309:Auditory Threshold / Q000502:physiology*; D002498:Centrifugation; D006801:Humans; D008297:Male; D008875:Middle Aged; D009622:Noise; D010470:Perceptual Masking / Q000502:physiology*