The role played by tool-use and tool-length on the Plastic Elongation of peri-hand space: a single case study

Consistent with neurophysiological findings showing expansion of the visual RF of visuo-tactile neurons along the rake used by monkeys to retrieve out-of-hand-reach objects (Iriki, Tanaka, & Iwamura, 1996), we have previously shown that also in humans the use of a tool can increase the spatial extent of the representation of peri-hand space, as revealed by an increase in the severity of cross-modal extinction after tool use (Farne & Ladavas, 2000). Here we further explored the characteristics of such a transient elongation of the multisensory peri-hand space representation in a patient with visual-tactile extinction. By investigating the variation of cross-modal extinction following different types of tool-related experience, we found that passive exposure to the tool is not sufficient per se to induce peri-hand space extension, which instead requires that the tool is used. This increase of peri-hand extension might be related to the physical length of the tool.