No handedness effect on spatial orientation or ocular counter-roll during lateral head tilts.

Although vestibular inputs are bilaterally represented within the cerebral hemispheres, the higher level vestibular functions exhibit hemispheric asymmetries. Previous studies have suggested that such asymmetries are associated with handedness. Here, we studied the impact of handedness (i.e., hemispheric lateralization) on spatial orientation using a subjective visual vertical (SVV) task. We tested 22 right-handed and 22 left-handed subjects in upright position, during prolonged lateral head tilts of 20° (~15 min), and after the head returned to upright position. The corresponding changes in torsional eye position were measured simultaneously using video-oculography. During lateral head tilts, both right- and left-handers had initial SVV biases in the opposite direction of the head tilt (right-handers: left tilt 3.0 ± 1.3°, right tilt -4.7 ± 1.5°; left-handers: left tilt 3.4 ± 1.1°, right tilt -4.1 ± 1.0°). The SVV subsequently drifted in the direction of the head tilt, and there was an aftereffect in the same direction when the head was brought back upright. The ocular torsion initially changed in the opposite direction of the head tilt (right-handers: left tilt 3.8 ± 0.4°, right tilt -3.8 ± 0.4°; left-handers: left tilt 4.2 ± 0.5°, right tilt -4.5 ± 0.5°), and there were also drift and aftereffect in the same direction as the head tilt. The changes in upright perception and ocular torsion did not differ between right- and left-handers. These findings show no functional laterality, neither in the higher level neural mechanisms that maintain spatial orientation, nor in the lower level mechanisms that generate the ocular torsion response during lateral head tilt.