Limb assignment with pointing responses (A058)

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.

学界普遍认为，触摸的皮肤位置默认会被重编码为三维空间位置。本实验中，人类被试在同一肢体或两个不同肢体上接收成对触觉刺激，并需判断刺激是否呈现于同一肢体，或是空间的同侧。通过肢体交叉使皮肤位置编码与三维空间编码产生错位，该操作对空间判断的影响强于对肢体判断的影响，这与"触摸的三维位置可被直接获取"的观点相悖。此外，当成对刺激位于同一皮节（dermatome）时，肢体交叉的效应会显著减弱，这表明肢体判断基于解剖学而非三维空间的刺激信息。上述结果表明，在三维空间中被编码的是肢体，而非触觉本身。学界常见的身体触觉位置报告误差，源于被试混淆了受触肢体的常规位置与当前动作相关肢体的空间布局。