The wheelchair as a full-body tool extending the peripersonal space

Abstract

Dedicated multisensory mechanisms in the brain represent peripersonal space (PPS), a limited portion of space immediately surrounding the body. Previous studies have illustrated the malleability of PPS representation through hand-object interaction, showing that tool use extends the limits of the hand-centered PPS. In the present study we investigated the effects of a special tool, the wheelchair, in extending the action possibilities of the whole body. We used a behavioral measure to quantify the extension of the PPS around the body before and after Active (Experiment 1) and Passive (Experiment 2) training with a wheelchair and when participants were blindfolded (Experiment 3). Results suggest that a wheelchair-mediated passive exploration of far space extended PPS representation. This effect was specifically related to the possibility of receiving information from the environment through vision, since no extension effect was found when participants were blindfolded. Surprisingly, the active motor training did not induce any modification in PPS representation, probably because the wheelchair maneuver was demanding for non-expert users and thus they may have prioritized processing of information from close to the wheelchair rather than at far spatial locations. Our results suggest that plasticity in PPS representation after tool use seems not to strictly depend on active use of the tool itself, but is triggered by simultaneous processing of information from the body and the space where the body acts in the environment, which is more extended in the case of wheelchair use. These results contribute to our understanding of the mechanisms underlying body-environment interaction for developing and improving applications of assistive technological devices in different clinical populations.

Keywords: assistive device; embodiment; peripersonal space; tool use; visual spatial exploration.

FIGURE 1

Audio–tactile interaction task. (A) Schematic representation of sound distances respect to the participants’ location. Participants where asked to respond as fast as possible to tactile stimulation on their trunk (symbolized by the yellow flash in figure), while two arrays of loudspeakers generated a sound stimulus starting from the far space and approaching the participants, either in the front or back space. (B) Picture of the experimental set up.

FIGURE 2

The graph shows participants’ mean responses to the tactile target at different temporal delays from sound onset in Experiment 1 (active use of the wheelchair). Hatched line refers to Active Pre training condition while filled line refers to the Active Post training condition. The red line indicates the position of the subject. The shaded region indicates the boundaries of peripersonal space (PPS). Error bars denote SEM.

FIGURE 3

The graph shows participants’ mean responses to the tactile target at different temporal delays from sound onset in Experiment 2 (passive use of the wheelchair). Hatched line refers to Passive Pre training condition while filled line refers to the Passive Post training condition. The shaded region indicates the initial boundaries of PPS (in gray) and their expansion after passive use of the wheelchair (in light gray). The red arrows indicate the direction of PPS enlargement. The red line indicates the position of the subject. Error bars denote SEM.

FIGURE 4

The graph shows participants’ mean responses to the tactile target at different temporal delays from sound onset in Experiment 3 (Passive use of the wheelchair in absence of visual information). Hatched line refers to No-Sight Pre training condition while filled line refers to the No-Sight Post training condition. The red line indicates the position of the subject. The shaded region indicates the boundaries of PPS. Error bars denote SEM.

FIGURE 5

The plot shows the mean subjective ratings for items describing functional aspects of wheelchair embodiment in the three groups of participants. The error bars indicate the SEM. The arrows indicate significant results from the post hoc comparisons (p < 0.05).