Case study: Head orientation and neck electromyography for cursor control in persons with high cervical tetraplegia.

We evaluated the ability of an individual with a high cervical spinal cord injury (SCI) to control a cursor on a computer screen using two different user interfaces: (1) head movements measured via a head-mounted orientation sensor and (2) electromyography (EMG) signals from four head and neck muscles acquired using a 4-channel implanted upper-limb neuroprosthesis that had been deployed in an earlier study. The subject moved the cursor to a set of targets on the screen in a two-dimensional, center-out, target-acquisition task, and his performance was evaluated with a variety of performance measures to assess both position and velocity control accuracy. The subject's performance with both command sources was also compared with the performance of a group of nondisabled subjects. Head orientation provided more accurate performance but was less responsive than EMG. Both command sources showed some directionally dependent performance, with movement to diagonally located targets being performed by a series of sequential motions rather than via straight paths. Overall, the SCI subject's performance with each command source was similar to that reported for a nondisabled population using the same interfaces and performing the same task.