  Clinical myoelectric prostheses lack the sensory feedback and sufficient
dexterity required to complete activities of daily living efficiently and
accurately. Providing haptic feedback of relevant environmental cues to the
user or imbuing the prosthesis with autonomous control authority have been
separately shown to improve prosthesis utility. Few studies, however, have
investigated the effect of combining these two approaches in a shared control
paradigm, and none have evaluated such an approach from the perspective of
neural efficiency (the relationship between task performance and mental effort
measured directly from the brain). In this work, we analyzed the neural
efficiency of 30 non-amputee participants in a grasp-and-lift task of a brittle
object. Here, a myoelectric prosthesis featuring vibrotactile feedback of grip
force and autonomous control of grasping was compared with a standard
myoelectric prosthesis with and without vibrotactile feedback. As a measure of
mental effort, we captured the prefrontal cortex activity changes using
functional near infrared spectroscopy during the experiment. Results showed
that only the haptic shared control system enabled users to achieve high neural
efficiency, and that vibrotactile feedback was important for grasping with the
appropriate grip force. These results indicate that the haptic shared control
system synergistically combines the benefits of haptic feedback and autonomous
controllers, and is well-poised to inform such hybrid advancements in
myoelectric prosthesis technology.
