Precise tactile localization on tools in two dimensions.

The ability to localize touch on the skin is a fundamental perceptual skill. Recent results show that this ability extends to hand-held tools, allowing participants to precisely localize along a rod's length. This tool-based localization may involve repurposing body-based somatosensory mechanisms. It remains unclear whether precise localization is limited to one-dimensional tools aligned with the long axis of the arm. Here, we show that touch can be localized along multiple dimensions of a held object. Participants held a square board while we measured tactile localization performance. Accuracy was well above chance, both overall and for both the proximodistal and medio-lateral axes. Notably, localization was more precise in the medio-lateral axis, reflecting an anisotropy similar to tactile perception on the skin. This anisotropy was defined in a hand-centered reference frame. These results show that wielded objects can be integrated with the somatosensory system, allowing rich tactile perception from tools.