The head midline as a reliable reference frame for encoding head-on-body orientation

Twelve right-handed male subjects were asked to use each hand to point accurately toward the center of their forehead, determining the correct position according to their mental representation, while the head was either aligned with the trunk or tilted 30 degrees to the right or left. Analysis of end-positions of pointing revealed that the right hand exhibited a slight leftward bias with respect to the putative head midline passing through the center of the glabella and the center of the fissure between the two upper central incisors, regardless of the head-on-body orientation, whereas the left hand proved very accurate when the head was aligned with the trunk but, when the head was tilted either way, it deviated to the opposite side. These results lead to the conclusion that the head midline appears to act as a reliable reference frame for encoding head-on-body orientation when pointing is carried out by the dominant hand.