Sign language is often spoken of as a “manual” language, meaning that the signers’ hands produce the language. But in fact there is a much more to the language then simply hand motion. Facial expressions, head and body movements, and posture all factor into the meaning of the signs. One study suggests that ASL should more appropriately be described as a “visual-gestural language—where gesture is a generic term referring to body movement.”

Facial expression and body movement help form the sign. They add intensity. They provide grammatical and prosodic information. They also act as adverbs or adjectives. A particular combination of movements determine whether a sentence is a question, an assertion, or a command. It can also indicate negation or structural information about the sentence.

The Facial Action Coding System (FACS) has been used to identify the universal movements of when people experience one of the six basic emotions (happiness, fear, sadness, disgust, anger, surprise). But now it’s been used to code expressions in ASL. The results below show what behaviors occur with various types of questions when signed in ASL. These behaviors indicate eyebrow raise, eyelid movements, and altered eyebrow shape. Slight changes in facial position determine what type of question is being posed.
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Baker-Shenk, Charlotte. “The Facial Behavior of Deaf Signers: Evidence of a Complex Language.” American Annals of the Deaf 130.4 (1985): 297-304. Project MUSE. Web. 13 Nov. 2014.