title: Unipedal balance in healthy adults: effect of visual environments yielding decreased lateral velocity feedback.
abstract: OBJECTIVE
  To test the (null) hypotheses that the reliability of unipedal balance is unaffected by the attenuation of visual velocity feedback and that, relative to baseline performance, deterioration of balance success rates from attenuated visual velocity feedback will not differ between groups of young men and older women, and the presence (or absence) of a vertical foreground object will not affect balance success rates.
  
  
  METHODS
  Single blind, single case study.
  
  
  METHODS
  University research laboratory.
  
  
  METHODS
  Two volunteer samples: 26 healthy young men (mean age, 20.0yrs; SD, 1.6); 23 healthy older women (mean age, 64.9 yrs; SD, 7.8).
  
  
  METHODS
  Normalized success rates in unipedal balance task.
  
  
  METHODS
  Subjects were asked to transfer to and maintain unipedal stance for 5 seconds in a task near the limit of their balance capabilities. Subjects completed 64 trials: 54 trials of three experimental visual scenes in blocked randomized sequences of 18 trials and 10 trials in a normal visual environment. The experimental scenes included two that provided strong velocity/weak position feedback, one of which had a vertical foreground object (SVWP+) and one without (SVWP-), and one scene providing weak velocity/strong position (WVSP) feedback. Subjects' success rates in the experimental environments were normalized by the success rate in the normal environment in order to allow comparisons between subjects using a mixed model repeated measures analysis of variance.
  
  
  RESULTS
  The normalized success rate was significantly greater in SVWP+ than in WVSP (p = .0001) and SVWP- (p = .013). Visual feedback significantly affected the normalized unipedal balance success rates (p = .001); neither the group effect nor the group X visual environment interaction was significant (p = .9362 and p = .5634, respectively). Normalized success rates did not differ significantly between the young men and older women in any visual environment.
  
  
  CONCLUSIONS
  Near the limit of the young men's or older women's balance capability, the reliability of transfer to unipedal balance was adversely affected by visual environments offering attenuated visual velocity feedback cues and those devoid of vertical foreground objects.
authors.affiliation: Department of Biomedical Engineering, University of Michigan, Ann Arbor 48109-2125, USA.
authors.forename: T W
authors.initials: TW
authors.lastname: Deyer
authors.forename: J A
authors.initials: JA
authors.lastname: Ashton-Miller
mesh_terms: D000328:Adult; D000368:Aged; D000375:Aging / Q000502:physiology*; D001288:Attention / Q000502:physiology; D005246:Feedback / Q000502:physiology*; D005260:Female; D007839:Functional Laterality / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009039:Motion Perception / Q000502:physiology; D004856:Postural Balance / Q000502:physiology*; D012016:Reference Values; D016037:Single-Blind Method; D012931:Social Environment; D014796:Visual Perception / Q000502:physiology*