The Body-Machine Interface: A New Perspective on an Old Theme

ABSTRACT

Body-machine interfaces establish a way to interact with a variety of devices, allowing their users to extend the limits of their performance. Recent advances in this field, ranging from computer interfaces to bionic limbs, have had important consequences for people with movement disorders. The authors provide an overview of the basic concepts underlying the body-machine interface with special emphasis on their use for rehabilitation and for operating assistive devices. They outline the steps involved in building such an interface and highlight the critical role of body-machine interfaces in addressing theoretical issues in motor control as well as their utility in movement rehabilitation.

Keywords:

• brain-machine interface
• dimensionality reduction
• redundancy
• rehabilitation
• robotics
• wheelchair

ACKNOWLEDGMENTS

This work was supported by grants 1R21HD053608 and 1R01NS05358 from the National Institutes of Health.

Notes

The body-machine interface also shares the abbreviation (BMI) with the better known brain-machine interface. This is not merely a coincidence or an accident of language, as there are significant commonalities between the two concepts. In both cases, the technological challenge is to decode information about motor intent and encode information about the state of a controlled device into some kind of sensory stimulus. If rejecting the separation between mind and body it is possible to agree that the brain-machine interface is a particular instantiation—perhaps the most striking—of the body-machine interface.

The term manifold was used instead of space because the theory refers to the nonlinear geometry of the configuration space of humans and animals. So, for example, the map from the arm configuration, expressed in terms of joint angles, to the position of the index finger, expressed in Cartesian coordinates, defines regions of angular coordinates that correspond to the same position of the finger tip. These regions are generally curved surfaces rather than flat linear spaces.