Radial trunk-centred reference frame in haptic perception

The shape of objects is typically identified through active touch. The accrual of spatial information by the hand over time requires the continuous integration of tactile and movement information. Sensory inputs arising from one single sensory source gives rise to an infinite number of possible touched locations in space. This observation raises the question of the determination of a common reference frame that might be employed by humans to resolve spatial ambiguity. Here, we employ a paradigm where observers reconstruct the spatial attributes of a triangle from tactile inputs applied to a stationary hand correlated with the voluntary movements of the other hand. We varied the orientation of the hands with respect to one another and to the trunk, and tested three distinct hypotheses regarding a reference frame used for integration: a hand-centred, a trunk-centred or an allocentric reference frame. The results indicated strongly that the integration of movement information and tactile inputs was performed in a radial trunk-centred reference frame.