Effector movement triggers gaze-dependent spatial coding of tactile and proprioceptive-tactile reach targets

Reaching in space requires that the target and the hand are represented in the same coordinate system. While studies on visually-guided reaching consistently demonstrate the use of a gaze-dependent spatial reference frame, controversial results exist in the somatosensory domain. We investigated whether effector movement (eye or arm/hand) after target presentation and before reaching leads to gaze-dependent coding of somatosensory targets. Subjects reached to a felt target while directing gaze towards one of seven fixation locations. Touches were applied to the fingertip(s) of the left hand (proprioceptive-tactile targets) or to the dorsal surface of the left forearm (tactile targets). Effector movement was varied in terms of movement of the target limb or a gaze shift. Horizontal reach errors systematically varied as a function of gaze when a movement of either the target effector or gaze was introduced. However, we found no effect of gaze on horizontal reach errors when a movement was absent before the reach. These findings were comparable for tactile and proprioceptive-tactile targets. Our results suggest that effector movement promotes a switch from a gaze-independent to a gaze-dependent representation of somatosensory reach targets.