Task Load Affects Tool Embodiment During Virtual Tool-use Training with Visual and Visuo-tactile Modalities in Healthy Aging

We previously reported that after virtual tool use training, younger as compared to older adults experienced a higher sense of ownership over virtual tools associated with changes in sensorimotor representation (i.e., body schema). Moreover, higher agency ratings were contingent on their performance levels and the extent to which the virtual tool was integrated into their arm representation. In contrast, older adults exhibited a heightened sense of agency, which was strongly associated with improvements in virtual tool use. Regardless, no changes to their body schema, and no emergence of a sense of ownership was revealed in older adults. Comparing data from a questionnaire and an analogue scale as two subjective measurements of embodiment during and after virtual tool-use training, we investigated whether this tool embodiment in both age groups could be predicted by task load assessed with the NASA TLX where participants rated their perceived task load related to the tool-use task in six dimensions (mental, physical, temporal, effort, performance and frustration). Data from 34 younger and 39 healthy older adults were analysed. Results revealed, that in younger adults mental load led to increased ownership over the virtual tool, and physical load negatively affected agency. Older adults showed weaker effects, with performance load being the only significant predictor of higher agency ratings. The analogue scale more directly captured the sense of control as it was collected during virtual tool use training blocks, while the questionnaire was used only after participants completed training blocks. Our results highlight age-related differences in how various dimensions of task load affect perceived ownership and agency during virtual tool use, suggesting the benefit of using multiple measures of ownership and agency for a more comprehensive understanding.