A lifespan study on body schema and perceived reaching distance

The plasticity of body representation in response to tool use is a dynamic process that evolves across the lifespan. Research has shown that tools can become integrated into the body representation, effectively being treated as extensions of the body. However, this incorporation is age-dependent, reflecting the ongoing development, stabilization, and potential decline of sensorimotor integration and body representation mechanisms. In this study, we explored how age influences the plasticity of the body schema and perceived reaching distance during short-term tool-use training within near and far space. Eighty-four participants spanning various age groups (12-80 years old) participated in two experimental sessions, utilizing a well-established tool-use paradigm to manipulate objects within both near and far spaces. To assess changes in body schema, a tactile distance judgment test was administered on the forearm in the proximodistal orientation. Furthermore, we employed a reaching distance estimation task to evaluate perceived reaching distance prior and after tool-use training. Across all age groups, participants showed reduced distance estimation between tactile stimuli on the forearm, but tool-use training did not produce any significant changes in these judgments. Findings further revealed no significant changes in perceived reaching distance after tool-use training over either near or far distances. We conclude that, although a large body of prior literature reports tool-use effects on body representational plasticity, our findings indicate that short-term tool-use does not significantly alter tactile distance perception of the forearm or perceived reaching distance across age groups. This suggests that brief tool-use exposure may be insufficient to induce lasting sensorimotor adaptations, and that more prolonged or immersive training may be required. While tool-use proficiency improves with age, the fundamental integration of tools into body representation appears to remain stable across the lifespan.