title: Flight display dynamics and compensatory head movements in pilots.
abstract: BACKGROUND
  Experiments measured the optokinetic cervical reflex (OKCR), wherein the banking pilot aligns the head with the horizon. In a synthetic cockpit, the flight display was manipulated to test whether changing the visual reference frame would alter OKCR.
  
  
  METHODS
  Eight subjects (five rated pilots) flew a route in simulated visual meteorological conditions that required them to bank the aircraft frequently. Pilots' head tilt was characterized using both the conventional method of regressing against simultaneous aircraft bank, and also an event-based analysis, which identified head movements before, during, and after each turn. Three display configurations were compared to determine whether pilots' orientation would ever migrate from the horizon to the aircraft symbol. The first was a conventional "Inside-Out" condition. A "Frequency-Separated" condition combined Inside-Out horizon geometry with Outside-In dynamics for the aircraft symbol, which depicted joystick bank inputs. In the "Outside-In" condition, the aircraft symbol rolled against a static horizon.
  
  
  RESULTS
  Regressions identified an interaction (p < 0.001) between display condition and aircraft bank: head tilt followed horizon tilt in Inside-Out and Frequency-Separated conditions, while remaining mostly level in the Outside-In condition. The event-based analysis identified anticipatory head movements in Inside-Out and Frequency-Separated conditions: 95% CI indicated that before each turn, head tilt favored the direction of the imminent bank.
  
  
  CONCLUSIONS
  While the conventional analysis confirmed that the horizon comprises a primary spatial reference, the finer-grained event-based analysis indicated that pilots' reference can migrate at least temporarily to the vehicle, and that OKCR can be preceded by anticipatory head movements in the opposite direction.
authors.affiliation: Laser Vehicle Engagement Simulator Laboratory, Naval Health Research Center Directed Energy Bioeffects Laboratory: NHRC DET DEBL, 8315 Navy Road, Brooks AFB, TX 78235-5365, USA. Jeremy.Beer@navy.brooks.af.mil
authors.forename: Jeremy
authors.initials: J
authors.lastname: Beer
authors.forename: David
authors.initials: D
authors.lastname: Freeman
mesh_terms: D000060:Accidents, Aviation / Q000517:prevention & control; D000328:Adult; D000337:Aerospace Medicine; D000401:Aircraft; D001359:Aviation; D019416:Head Movements / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D008889:Military Personnel; D017120:Nystagmus, Optokinetic / Q000502:physiology*; D012018:Reflex / Q000502:physiology*; D012027:Reflex, Vestibulo-Ocular / Q000502:physiology*; D013028:Space Perception / Q000502:physiology; D013037:Spatial Behavior / Q000502:physiology; D013647:Task Performance and Analysis; D014584:User-Computer Interface; D014786:Vision Disorders; D014796:Visual Perception / Q000502:physiology