Gender and line size factors modulate the deviations of the subjective visual vertical induced by head tilt

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.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.On Earth, humans need to have a sense of verticality. In sensorimotor terms, our upright, bipedal, postural stance is mediated by vestibular, somesthetic and visual inputs that serve as indicators of any deviation from the vertical. On the cognitive level, our vertical perception defines a gravitational reference frame, which subserves the coding of the location and orientation of objects in the environment independently of the observer's own orientation. Consequently, the subjective vertical (SV, i.e. the subjective estimation of gravitational direction) is commonly considered as an indicator of the sense of orientation. The SV is measured by asking the observer to align a light bar with the direction of gravity (i.e. the subjective visual vertical, SVV). Other modalities (such as the haptic modality) have been also used (e.g. [1-9]).The SVV arises from the complex integration of inputs from vestibular, visual, proprioceptive and tactile receptors. It has been clearly established that subcortical structures are involved in the vestibular contribution to oculomotor control (vestibulo-oculomotor reflexes) and postural control (vestibulo-collic and vestibulo-spinal reflexes) (for a review, see [10]). However, it is not known precisely how and where in the cortex the vestibular information on spatial cognition (and on