title: Number of sampling movements and manual stiffness judgments.
abstract: OBJECTIVE
  It has been suggested that when using posteroanterior pressure to assess the stiffness of the spine, no more than two or three oscillations should be used. This study sought to examine this clinical impression by investigating the effect of the number of sampling movements on stiffness perception.
  
  
  METHODS
  Perceptual study using a mechanical device to provide stiffness stimuli, with university staff and students as judges.
  
  
  METHODS
  University psychophysics laboratory.
  
  
  METHODS
  In part 1, subjects were directed to sample the stimuli a prescribed number of times (either 1, 2, 3, 4 or 5 pushes), whereas in part 2, subjects were free to choose the number of sampling movements.
  
  
  METHODS
  Measures of interstimulus discriminability and bias.
  
  
  RESULTS
  An inverted-U relationship between the number of directed sampling movements and stiffness discriminability was found, with three cycles providing best discriminability. When subjects were given a choice, most chose to use three cycles. The number of sampling movements had no effect on bias.
  
  
  CONCLUSIONS
  This study confirms the hypothesis under investigation and suggests that therapists will be maximally sensitive when using three testing cycles of posteroanterior pressure to assess stiffness.
authors.affiliation: John Hunter Hospital, Newcastle NSW, Australia.
authors.forename: N
authors.initials: N
authors.lastname: Macfadyen
authors.forename: C G
authors.initials: CG
authors.lastname: Maher
authors.forename: R
authors.initials: R
authors.lastname: Adams
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D006801:Humans; D020393:Manipulation, Spinal; D009068:Movement; D010173:Palpation; D010465:Perception; D011601:Psychophysics; D012372:ROC Curve; D013131:Spine / Q000502:physiology*; D013223:Statistics as Topic