title: Effects of fore-and-aft, lateral and vertical whole-body vibration on a head-positioning task.
abstract: BACKGROUND
  The performance of tasks in which the head must be positioned close to objects in a moving vehicle may be impeded by the presence of vibration.
  
  
  OBJECTIVE
  It was hypothesized that the extent to which a head positioning task would be impeded by whole-body vibration would depend on the frequency, direction and waveform of the vibration and the posture of the body.
  
  
  METHODS
  There were 12 subjects who participated in a laboratory experiment in which they judged the difficulty of looking through a pair of sights while exposed to low frequency vibration. We investigated 4 variables: vibration axis (fore-and-aft, lateral, vertical), vibration frequency (11 frequencies in the range 0.5 to 5.0 Hz), vibration waveform (sinusoidal vibration, one-third octave bands of random vibration), seating condition (wearing a 4-point harness, sitting without back support).
  
  
  RESULTS
  We found that all variables affected the perceived task difficulty. Frequencies of horizontal vibration in the range 1 to 4 Hz caused most difficulty. Task difficulty was greatest with random vibration, especially with low frequency vibration in the horizontal axes. The wearing of a 4-point harness greatly reduced the perceived task difficulty during exposure to low frequency fore-and-aft vibration but increased task difficulty with higher frequencies of lateral vibration.
  
  
  CONCLUSIONS
  Increased motion predictability and the provision of suitable support to the upper body (e.g., a harness, back support, front support) can reduce the difficulty of head positioning tasks during exposure to some types of oscillatory motion.
authors.affiliation: Human Factors Research Unit, University of Southampton, U.K.
authors.forename: M J
authors.initials: MJ
authors.lastname: Griffin
authors.forename: M W
authors.initials: MW
authors.lastname: Brett
mesh_terms: D000328:Adult; D006801:Humans; D008297:Male; D013647:Task Performance and Analysis; D014732:Vibration