Non-Manual Signs

Components of sign language that are produced without the hands, including facial expressions, mouth movements, eye gaze direction, head tilts, body posture, and shoulder shifts. Non-manual signs are not merely expressive additions but are grammatically essential in sign languages — they can indicate questions (raised eyebrows for yes/no questions, furrowed brows for wh-questions), negation, conditional clauses, relative clauses, and topic markers. A signed sentence without the appropriate non-manual markers can be meaningless or convey entirely the wrong meaning. Non-manual signs present a significant challenge for sign language technology, including signing avatars and sign language recognition systems, which must accurately produce or detect these subtle multi-channel signals alongside manual signs to be linguistically correct.