The body, from experience to representation

The concept of Peripersonal space (PS) refers to a limited space surrounding the body where visual, auditory and tactile inputs are integrated. PS can be extended by a brief use of a tool to reach objects place in the far space. Here we investigated whether long term experience of tool-use can result in a durable extension of PS. We studied audio-tactile integration in blind subjects using a cane to navigate in everyday life and in sighted subjects. Participants performed a speeded tactile discrimination task at the dominant hand, with task-irrelevant concurrent sounds being presented either nearby or at a distance from the hand approximating the length of a blind cane. In sighted participants, RT to tactile stimuli were faster when sounds were given near their hand, this suggesting that acoustic and tactile stimuli are integrated in a limited space surrounding the hand. After a brief experience using the cane to explore a dark space, RT difference was reduced. The same difference reappeared after one day of not using the tool. Therefore, in sighted subjects auditory PS expanded or contracted following tool-use. On the contrary, blind subjects immediately responded faster to tactile stimuli associated with far sounds rather than with near sounds. This happened only when they held the cane, whereas, if they held a short handle, their results were as in sighted subjects. This suggests that long term experience with the cane induce an extended representation of the PS, selectively activated by the cane.