Tool embodiment across the lifespan

Research has consistently shown that expertise in tool-use is associated with a phenomenon known as tool embodiment. Additionally, prior research has shown that higher ownership ratings over virtual tools in young adults are predicted by a reduction in perceived tactile distance of the forearm, whereas the sense of agency over virtual tools appears to arise independently of changes in perceptual estimation. In this study, we investigated whether the subjective ratings of ownership and agency over tools of different sizes used for grasping objects in both near and far space can be predicted by forearm tactile distance perception and perceived reaching distance (RDE). Additionally, we tested whether this embodiment process varies across the lifespan. Participants aged 12 to 80 years completed two experimental sessions using a well-established tool-use paradigm to manipulate objects in both near (within arm's reach) and far space (beyond arm's reach). A tactile distance judgment (TDJ) task was administered on the forearm in the proximodistal orientation. Subjective ratings of ownership and agency over the tool were collected through a post-task questionnaire. Results revealed significant effects of age and training space on ownership ratings, along with robust three-way interactions involving residual tactile distance estimation error and perceived reaching distance error. Overall, results revealed higher subjective ratings of ownership over the tool in adolescents and young adults compared to other age groups independent of training space. Results further revealed higher subjective ratings of ownership are significantly predicted by reduced forearm tactile distance estimation error in adolescents and young adults compared to middle-aged group in the far training condition. Higher ratings of agency over the tool were also significantly predicted by perceived forearm tactile distance interactively with training space conditions and age, however, effects were not significantly different dependent on age or training space condition. In addition, perceived reaching distance estimation error significantly predicted higher ratings of ownership and agency over the tool. More specifically, higher ratings of ownership were significantly predicted in adolescents and young adults compared to middle-aged adults in far space. For agency, however, higher ratings were predicted by perceived reaching distance independent of age or training space. Collectively, these results suggest that sensorimotor-based embodiment experiences, especially the extent that the ownership is perceived over the tool, are modulated by both perceived reaching distance and forearm tactile distance perception, with effects being most pronounced in adolescents and young adults.