title: Anisotropy and spatial tactile acuity on human lips.
abstract: OBJECTIVE
  To investigate tactile anisotropy on human lips.
  
  
  METHODS
  Spatial tactile acuity was assessed with a three-alternative, forced-choice grating orientation task. Circular probes with horizontal (parallel to lip), vertical (perpendicular to lip), or oblique (45° right of vertical) grooves and ridges of equal width were applied (n=60) to the midline of each lip. Participants (n=13) were asked to state the grating orientation whilst blindfolded. The percentage of correct responses was plotted as a function of the log gap width. Data were fitted with a four-parameter sigmoid function. Response bias was assessed (n=13) with application of a smooth polished Perspex probe. 65.5%, 71.5%, and 63.0% correct was adopted as the threshold estimate for the vertical, horizontal, and oblique orientations based on the measured response bias.
  
  
  RESULTS
  Across orientations, the threshold on the upper lip (1.5 ± 0.9 mm) was significantly greater than on the lower lip (1.0 ± 0.7 mm; P=0.006). However, there was no significant main effect of orientation or orientation-by-lip interaction on threshold.
  
  
  CONCLUSIONS
  Tactile anisotropy is absent on human lips.
  
  
  CONCLUSIONS
  The lack of anisotropy is surprising given that anisotropy is present on fingers and that afferent input and sensory processing for human lips and fingers share similarities.
authors.affiliation: Discipline of Physiology, University of Adelaide, Adelaide, Australia. gabrielle.todd@unisa.edu.au
authors.forename: Gabrielle
authors.initials: G
authors.lastname: Todd
mesh_terms: D000328:Adult; D016880:Anisotropy; D005260:Female; D006801:Humans; D008046:Lip / Q000502:physiology*; D008297:Male; D009949:Orientation / Q000502:physiology; D012684:Sensory Thresholds / Q000502:physiology; D014110:Touch / Q000502:physiology*; D055698:Touch Perception / Q000502:physiology*