Embodiment of a functionally altered virtual arm in children and adults

This study aimed to investigate whether human embodiment is dependent on the sensorimotor functions of one’s body. We hypothesised that body function constrains both the sense of ownership and sensorimotor control of the body movements. We studied these relationships in the context of control of unilateral goal-directed forward arm reaching movements made with a virtual arm. In addition, we expected that children possess more adaptable body representations compared to adults, facilitating greater acceptance of virtual bodies with altered sensorimotor contingencies. We tested 5-7 and 8-10-year-old children, and young adults. Participants took part in an animal feeding game within a Virtual Reality environment. At each age, we manipulated the visual gain of hand movements to alter reaching functionality in three groups: compared to a normal (100%) gain, reaching arm length was slightly reduced (80%); slightly increased (120%); or greatly increased (400%). Parameters representing reach kinematics, subjective perception of arm length, and subjective limb embodiment were assessed during and after reaching with normal and altered control gain. In addition to changes in their reach kinematics, changes in subjective embodiment and reaching affordance were recorded compared to baseline reaching without altered visual gain. We found that the altered reaching functionality reduced Subjective ratings of limb ownership during exposure to the 400% visual gain modification in the group of adults only. In contrast, changes in reach kinematics occurred in all the age groups of children and adults, with age group-specific adjustments in the motor control strategy, characterised by altered magnitude and spatiotemporal placement of peak velocity as well as smoothness of reaching. Finally, at all ages subjective reaching affordance estimates were enhanced following exposure to the two functionality conditions with increased arm length. Our results indicate that the sense of ownership, accuracy of body representations, and characteristics of sensorimotor control are related to bodily function. In addition, it appears that these relationships might be more plastic, or perhaps more tolerant to functional alterations in terms of perceived ownership, in children compared to adults.