Does the Crossed-Limb Deficit Affect the Uncrossed Portions of Limbs?

When locating touch, we remap its location from skin-based to external coordinates as a function of body posture. While remapping is thought to occur whenever there is tactile input, research has focused on a special case, the crossed-hands deficit, where tactile localization is impaired when the limbs are crossed compared with uncrossed. To date, these studies have always stimulated portions of the limbs that are crossed, such as a finger of each hand. It is therefore unknown whether the deficit induced by arm crossing is specific to the crossed portion of the limb or affects the limb as a whole. In Experiments 1 and 2, we stimulated the shoulders and elbows and found that tactile localization, measured with temporal order judgments, was unaffected by crossing the forearms. In Experiment 3, a crossed-limbs deficit was observed for touches on a single skin location when that location was distal-but not proximal-to the crossing point of the arms. In Experiment 4, we found a similar crossed-limbs deficit irrespective of how far distally to the crossing point touch was applied. Together, these results demonstrate that crossing the limbs affects tactile perception only distal to the point of crossing. The process of remapping tactile events does not take into account the end-point location of the limb, but an extremely precise metric description of the touch relative to the configuration of both arms.