When Far Becomes Near: Remapping of Space by Tool Use

Abstract

Abstract& Far (extrapersonal) and near (peripersonal) spaces are behaviorally defined as the space outside the hand-reaching distance and the space within the hand-reaching distance. Animal and human studies have confirmed this distinction, showing that space is not homogeneously represented in the brain. In this paper we demonstrate that the coding of space as ''far'' and ''near'' is not only determined by the hand-reaching distance, but it is also dependent on how the brain represents the extension of the body space. We will show that when the cerebral representation of body space is extended to include objects or tools used by the subject, space previously mapped as far can be remapped as near. Patient P.P., after a right hemisphere stroke, showed a dissociation between near and far spaces in the manifestation of neglect. Indeed, in a line bisection task, neglect was apparent in near space, but not in far space when bisection in the far space was performed with a projection lightpen. However, when in the far space bisection was performed with a stick, used by the patient to reach the line, neglect appeared and was as severe as neglect in the near space. An artificial extension of the patient's body (the stick) caused a remapping of far space as near space. &

Spatial cognition: evidence from visual neglect

“…When lines of constant visual angle are bisected by laser pen in near versus far space, some patients show accurate performance in far space but a significant rightward deviation in near space, [22,23] whereas other patients show the reverse dissociation: far left neglect without near left neglect [24,25]. These positive findings contrast with an early failure to show dissociations between near and far left neglect when perceptual tasks with no manual component were used [26].…”

“…How, in these circumstances, does the brain encode this enlarged peripersonal space? Berti and Frassinetti [23] reported a patient who showed clear left neglect on a range of tasks (including bisection) in near space but little or no neglect on bisection when using a laser pointer to operate in far space. Yet when a long stick was substituted for the laser pointer, significant left neglect was again manifest.…”

Tool use changes multisensory interactions in seconds: evidence from the crossmodal congruency task

“…In their study, the use of the four tools was pseudorandomly interleaved on a trial-by-trial basis. The fact that tool-length differences were found at all suggests that line bisection performance can be modulated on a very short timescale if not immediately upon using the tool (see also Berti and Frassinetti 2000). There is now a pressing need to account for the potentially different neural mechanisms and behavioural processes underlying these immediate (or trial-by-trial) effects, as compared to the longer-lasting effects of tool use training on multisensory interactions measured up to several minutes after tool use (see, for example, Weiss et al 2000 for a neuroimaging study of line bisection performance).…”

“…Interestingly, in one study of crossmodal extinction and tool use, the phase during which crossmodal extinction was tested was also the active tool use phase itself -i.e., this study followed a different, 'concurrent' design (Maravita et al 2001; see also Berti & Frassinetti 2000;Holmes et al 2007;Pegna et al 2001). The tool use task in Maravita and colleagues' experiment involved actively maintaining the tool in position, and checking the tool location repeatedly during the testing period, but between trials.…”

A novel approach to mechanical foot stimulation during human locomotion under body weight support

“…Nevertheless, the functional role of specific groups of sensory receptors in regulating human locomotion is still uncertain because they cannot be easily separated since they interact with each other and with central rhythm-generating centers in a complex manner. In addition, support surface and contact with a ground may also be included as components of our ego space in a similar way as external objects and tools can be included in our body scheme (Berti & Frassinetti, 2000;Iriki, Tanaka, & Iwamura, 1996;Ivanenko, Levik, Talis, & Gurfinkel, 1997;Solopova, Kazennikov, Deniskina, Levik, & Ivanenko, 2003).…”