  The emergence of robot-based body augmentation promises exciting innovations
that will inform robotics, human-machine interaction, and wearable electronics.
Even though augmentative devices like extra robotic arms and fingers in many
ways build on restorative technologies, they introduce unique challenges for
bidirectional human-machine collaboration. Can humans adapt and learn to
operate a new limb collaboratively with their biological limbs without
sacrificing their physical abilities? To successfully achieve robotic body
augmentation, we need to ensure that by giving a person an additional
(artificial) limb, we are not in fact trading off an existing (biological) one.
In this manuscript, we introduce the "Neural Resource Allocation" problem,
which distinguishes body augmentation from existing robotics paradigms such as
teleoperation and prosthetics. We discuss how to allow the effective and
effortless voluntary control of augmentative devices without compromising the
voluntary control of the biological body. In reviewing the relevant literature
on extra robotic fingers and limbs we critically assess the range of potential
solutions available for the "Neural Resource Allocation" problem. For this
purpose, we combine multiple perspectives from engineering and neuroscience
with considerations from human-machine interaction, sensory-motor integration,
ethics and law. Altogether we aim to define common foundations and operating
principles for the successful implementation of motor augmentation.

Robotics;Systems and Control;Systems and Control