Moving in space in a wheelchair: the embodiment of one’s own wheelchair and its effects on navigational space representation in people with spinal cord injury.

Recent studies suggest that cognitive functions change in spinal cord injured people1,2,3 (SCI), supporting to the theories that suggest a role for sensory-motor systems in cognition. Anecdotal reports indicate that SCI incorporate their wheelchair and modify the representation of navigational space. However, to date there are no experimental data. We tested two hypotheses: that SCI incorporate their own wheelchair and that this impacts on the representation of navigational space. 20 paraplegics with complete spinal lesions (i.e., the lower part of the body totally paralyzed and insensitive) participated in two experiments. In the first, embodiment was examined by exploiting the body enhancement effect (i.e., stimuli administered to the body are detected faster than those administered elsewhere). Participants were requested to click on a mouse-key when they saw an LED flashing. The LEDs were positioned on their trunk, their legs and on the wheelchair in three counterbalanced conditions: i) sitting in their wheelchair, ii) sitting in another wheelchair, or iii) with the LEDs on a wooden bar. The SCI’s responses were faster for LEDs positioned on the body and their own wheelchair than on the other wheelchair and the wooden bar. In the second experiment, participants had to assess the slope of a ramp and the distance of a flag rendered in virtual reality. Two counterbalanced conditions were compared with participants sitting in their own or in a different wheelchair. The results show that when sitting in their own wheelchair, participants estimated the spatial distance to be shorter than when sitting in another wheelchair. These results indicate that SCI incorporate their own wheelchair and that this modulates their representation of navigational space.