Embodiment of assistive tools in spinal cord injury: evidence from mental rotation tasks of wheelchairs and exoskeletons

Embodiment is a critical but underexplored aspect of human adaptation to assistive devices. Measures of embodiment can assess how well prostheses integrate into users' body schemas and improve functionality. This study utilized a mental rotation task to evaluate the functional embodiment of wheelchair and exoskeleton devices and how spinal cord injury affects body part representation. Twenty male participants with SCI lesions ranging from T4 to L2 were included, and measurements were taken pre and post-EXO training in two different times at baseline (T0, immediately before the start of the EXO training protocol) and after a 2-month exoskeleton training program to T1 (after the end of 10/14 EXO training). Twenty healthy participants with demographic characteristics similar to those of the clinical sample were recruited as control group. A mental rotation task of biological (hands/feet) and non-biological (wheelchair/exoskeleton) stimuli presented on a screen in 4 different orientations (0°, 90°, 180°, 270°) was administered. Subjects had to verbally indicate the laterality (right or left) of the presented stimulus. Accuracy and Reaction times(RTs) were collected. Also, participants were asked to complete the Mental Rotation Questionnaire to inspect strategies adopted during task execution and subjective opinions on the presented stimuli. Mixed ANOVAs on RTs considering between-group differences and within factors (type of stimulus, measurement time) were conducted. There was a significant group x stimulus interaction (p = 0.02). Post hoc comparisons revealed that healthy controls were slower than patients in wheelchair rotation(p = 0.03). Interestingly, ANOVA on RTs in the exoskeleton mental rotation shows a significant effect of time (p = 0.047) with a faster rotation time at T1 compared to T0. The significant effect of PRE/POST (p =0.02) indicates that the time required to rotate exoskeleton images is faster (PRE=1068, POST=968)immediately after the training, indicating a brief term plasticity. The study's findings indicate that the mental rotation abilities of wheelchairs and exoskeletons can reflect their integration into users' body representations, both in the short and long term. This has the potential to yield valuable insights into how users perceive and accept assistive devices. Incorporatingembodiment measures in evaluating new devices is crucial for promoting exoskeleton adoption and informing targeted rehabilitation strategies for patients with spinal cord injuries.