Non-Manual Signal

A linguistic component of sign languages that is expressed through parts of the body other than the hands, including facial expressions, eyebrow movement, head tilts, shoulder shifts, mouth movements, and eye gaze direction. Non-manual signals serve critical grammatical functions in sign languages — for example, in ASL, raised eyebrows indicate a yes/no question while furrowed eyebrows mark a wh-question. They can also modify meaning, indicate negation, mark topics, and convey prosody. Recognition and generation of non-manual signals is a major challenge for sign language technology systems.