Discrete vs. continuous surface electromyographic interface control

Over 50% of the 273,000 individuals with spinal cord injuries in the US have cervical injuries and are therefore unable to operate a keyboard and mouse with their hands. In this experiment, we compared two systems using surface electromyography (sEMG) recorded from facial muscles to control an onscreen keyboard. Both systems used five sEMG sensors to capture muscle activity during five distinct facial gestures that then mapped to five cursor commands: move left, move right, move up, move down, and click. One system used a discrete movement and feedback algorithm, in which the user would make one quick facial gesture, causing a corresponding discrete movement to an adjacent button. The other system was continuously updated and allowed the user to move in any 360º direction smoothly. Information transfer rates (ITRs) in bits per minute were high for both systems. Users of the continuous system showed significantly higher ITRs (average of 68.5; p < 0.02) compared to users of the discrete system (average of 54.3 bits/min).