A high cervical spinal cord injury can result in significant loss of function below the shoulders. Often, this function is restored through the use of adaptive computer technology or neuroprostheses. While these devices can help to restore function, they need a viable user interface. This project investigated the command sources available to an individual with high tetraplegia. A novel means of command source evaluation was developed for both 2D and 3D command sources. This included the use of original performance measures that served to illustrate the underlying aspects of performance. Two command sources applicable to the SCI community were studied, head orientation and EMG of muscles of the face and neck.
Able bodied subjects and an individual with an implanted neuroprosthesis with implanted EMG electrodes participated in a 2D Fitts’ Law task controlling a computer cursor using the command sources under investigation. The performance of a computer mouse was also explored. Performance was similar between subject populations. Head orientation was the superior command source over EMG for cursor control as it was much less affected my target direction. Users could more easily control two head orientations simultaneously to move to diagonal targets where EMG was used in a more sequential manner.
In a novel 3D, out-center Fitts’ Law task, able-bodied subjects used each command source as well as three-axis joystick to control the end-point of a robot arm and the performances evaluated. All three command sources exhibited similar behavior and performance as all were used in a sequential manner, producing a large effect of target dimensionality upon performance. Given its ease of implantability, EMG is the better choice for control of an implanted neuroprosthesis for restoration of hand and arm function.
The use of multiple performance measures in both tasks served to better portray the various aspects that make up the overall performance of a user interface. The use of a single summary measure alone is not enough, particularly when target dimensionality can have such a dramatic effect.