title: Gender and line size factors modulate the deviations of the subjective visual vertical induced by head tilt.
abstract: BACKGROUND
  The subjective visual vertical (SVV, the visual estimation of gravitational direction) is commonly considered as an indicator of the sense of orientation. The present study examined the impact of two methodological factors (the angle size of the stimulus and the participant's gender) on deviations of the SVV caused by head tilt. Forty healthy participants (20 men and 20 women) were asked to make visual vertical adjustments of a light bar with their head held vertically or roll-tilted by 30° to the left or to the right. Line angle sizes of 0.95° and 18.92° were presented.
  
  
  RESULTS
  The SVV tended to move in the direction of head tilt in women but away from the direction of head tilt in men. Moreover, the head-tilt effect was also modulated by the stimulus' angle size. The large angle size led to deviations in the direction of head-tilt, whereas the small angle size had the opposite effect.
  
  
  CONCLUSIONS
  Our results showed that gender and line angle size have an impact on the evaluation of the SVV. These findings must be taken into account in the growing body of research that uses the SVV paradigm in disease settings. Moreover, this methodological issue may explain (at least in part) the discrepancies found in the literature on the head-tilt effect.
authors.affiliation: Department of Psychology, University of Lille, Laboratory of Functional Neurosciences and Pathology EA4559, 4 rue du Barreau, Villeneuve d'Ascq, 59653, France. marion.luyat@univ-lille3.fr
authors.forename: Marion
authors.initials: M
authors.lastname: Luyat
authors.forename: Myriam
authors.initials: M
authors.lastname: Noël
authors.forename: Vincent
authors.initials: V
authors.lastname: Thery
authors.forename: Edouard
authors.initials: E
authors.lastname: Gentaz
mesh_terms: D000328:Adult; D005260:Female; D006257:Head / Q000502:physiology*; D019416:Head Movements / Q000502:physiology*; D006801:Humans; D008297:Male; D009949:Orientation / Q000502:physiology*; D011434:Proprioception / Q000502:physiology*; D012737:Sex Factors; D013028:Space Perception / Q000502:physiology; D014796:Visual Perception / Q000502:physiology