title: What you see is what you step: the horizontal-vertical illusion increases toe clearance in older adults during stair ascent.
abstract: OBJECTIVE
  Falls on stairs are a significant cause of morbidity and mortality in elderly people. A simple safety strategy to avoid tripping on stairs is increasing foot clearance. We determined whether a horizontal-vertical illusion superimposed onto stairs to create an illusory perceived increase in stair-riser height would increase stair ascent foot clearance in older participants.
  
  
  METHODS
  Preliminary experiments determined the optimum parameters for the horizontal-vertical illusion. Fourteen older adults (mean age ± 1 SD, 68.5 ± 7.4 years) ascended a three-step staircase with the optimized version of the horizontal-vertical illusion (spatial frequency: 12 cycles per stair riser) positioned either on the bottom or top stair only, or on the bottom and top stair simultaneously. These were compared to a control condition, which had a plain stair riser with edge highlighters positioned flush with each stair-tread edge. Foot clearance and measures of postural stability were compared across conditions.
  
  
  RESULTS
  The optimized illusion on the bottom and top stair led to a significant increase in foot clearance over the respective stair edge, compared to the control condition. There were no significant decreases in postural stability.
  
  
  CONCLUSIONS
  An optimized horizontal-vertical visual illusion led to significant increases in foot clearance in older adults when ascending a staircase, but the effects did not destabilize their postural stability. Inclusion of the horizontal-vertical illusion on raised surfaces (e.g., curbs) or the bottom and top stairs of staircases could improve stair ascent safety in older adults.
authors.affiliation: Bradford School of Optometry and Vision Science, University of Bradford, Bradford, United Kingdom.
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Foster
authors.affiliation: Bradford School of Optometry and Vision Science, University of Bradford, Bradford, United Kingdom.
authors.forename: David
authors.initials: D
authors.lastname: Whitaker
authors.affiliation: Faculty of Health Studies, University of Bradford, Bradford, United Kingdom.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Scally
authors.affiliation: Division of Medical Engineering, School of Engineering, University of Bradford, Bradford, United Kingdom.
authors.forename: John G
authors.initials: JG
authors.lastname: Buckley
authors.affiliation: Bradford School of Optometry and Vision Science, University of Bradford, Bradford, United Kingdom.
authors.forename: David B
authors.initials: DB
authors.lastname: Elliott
mesh_terms: D000058:Accidental Falls; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001696:Biomechanical Phenomena; D005260:Female; D005684:Gait / Q000502:physiology*; D006801:Humans; D007088:Illusions / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D004856:Postural Balance / Q000502:physiology*; D014034:Toes / Q000502:physiology*; D016138:Walking / Q000502:physiology*