Processing of peripersonal and extrapersonal space using tools: evidence from visual line bisection in real and virtual environments.

The dissociation between peripersonal space (within reaching) and extrapersonal space (beyond reaching) has been reported in studies using the line bisection task in left neglect patients and in healthy participants. Furthermore, this dissociation can be modulated by tool use. We conducted two experiments to compare line bisection in peripersonal (i.e., 30, 60cm) and extrapersonal space (i.e., 90, 120cm). Healthy participants bisected visual lines using sticks and a laser pointer, according to the experimental paradigm of Longo and Lourenco [On the nature of near space: Effects of tool use and the transition to far space. Neuropsychologia, 44, 977-981, 2006]. In Experiment 1 participants performed line bisection in a real environment, whereas in Experiment 2 participants performed line bisection in a virtual environment. Results from both experiments revealed an abrupt midpoint shift from the peripersonal to the extrapersonal space but only when a laser pointer was used. In addition, we confirmed that peripersonal space can be extended to extrapersonal space when participants used a stick. Notably, virtual reality can be a useful technique for studying the dissociation between peripersonal and extrapersonal space and their interaction by means of tool use.