Communicative hand gestures as an implicit measure of artificial limb embodiment and daily usage

When people talk, they move their hands to enhance meaning. Here we ask whether people spontaneously use their artificial limbs (prostheses) to gesture, and whether prosthesis gesture behaviour relates to everyday prosthesis use and perceived embodiment. One-handed participants with congenital and acquired hand loss and two-handed controls participated in gesture-facilitating tasks, measured using acceleration monitors and further validated with offline video coding. Everyday functional prosthesis use and perceived prosthesis embodiment were assessed using questionnaires. Perhaps surprisingly, one- and two-handed participants did not differ in the amount of gestures they produced. However, they did differ in their gesture profile. One-handers performed more, and bigger, movements with their intact hand while gesturing relative to their prosthesis, whereas two-handers produced more equal movements across hands. Importantly, one-handers who incorporated their prosthesis more into gesturing, that is -- produced gestures that were more similar to their two-handed counterparts -- also showed more frequent prosthesis use in day-to-day life. Although as a group, one-handers only marginally agreed that their prosthesis feels like a body-part, people reporting positive embodiment also showed great prosthesis habits, both for communication and daily function. We propose that measuring gesture behaviour in prosthesis-users can be used as an implicit and objective clinical tool to monitor and assess successful prosthesis adoption.