Limb, not touch location, is coded in 3D space

Abstract

Skin location of touch is said to be recoded, by default, into a 3D-spatial location. Here, human participants received tactile stimulus pairs on a common or on two different limbs and judged either whether stimuli had occurred on the same limb, or on a common side of space. Misaligning skin and 3D-spatial codes through limb crossing had a stronger effect on spatial than on limb judgments, contradicting the notion that the 3D location of touch is readily available. Additionally, crossing effects were significantly reduced when stimulus pairs lay in a common dermatome, suggesting that limb choice was based on anatomical, not 3D-spatial, stimulus information. These results suggest that it is limbs, not touch, which are coded in 3D space. Commonly observed errors in reporting where touch occurred on the body depend on confusion due to where the touched limb usually resides with the spatial layout of the currently action-relevant limbs.