What Are Sign Language Interpreters Mouthing?

The short answer

Interpreters are usually not chatting silently or whispering a translation to themselves. Their mouth movements are normally part of the signed message and fall into two kinds. Mouthings are silent, often shortened versions of spoken-language words. Mouth gestures are mouth shapes that belong to the sign language's own grammar and do not come from spoken words. How much an interpreter mouths, and which kind they use, depends on the sign language, the audience and the interpreter's style, so no single description fits every interpreter.

Mouthings: spoken words shown without voice

A mouthing is the visible shape of a spoken word, usually made without sound and often cut down to its first syllable or most visible sounds. An interpreter working in American Sign Language (ASL) may mouth English words alongside signs for several reasons:

• To distinguish signs that look the same or very similar on the hands but have different meanings.
• To support fingerspelled names, places, brand names and specialized vocabulary.
• To match the preference of deaf or hard-of-hearing audience members who use English-influenced signing or who combine signing with lipreading.

Mouthings do not form a word-for-word transcript that you can lipread. They are usually reduced, selective and timed to the signs, so lipreading an interpreter is an unreliable way to follow what the speaker is saying.

Mouth gestures: grammar on the face

Sign languages also use mouth shapes that have no spoken-word source. In ASL these are often called mouth morphemes. They change or add meaning to a sign much as an adverb or adjective does in English. ASL courses commonly teach examples such as these:

• MM: lips pressed together and pushed out slightly. Conveys that something is normal or relaxed, or that it is done with ease.
• CHA: the mouth opens sharply. Indicates something large, tall or plentiful.
• OO: rounded lips. Indicates something small or thin.
• TH: the tongue rests slightly between the teeth. Means carelessly or sloppily.
• CS: teeth clenched, with the cheek drawn toward the shoulder. Marks something very close in time or space, such as "just now" or "right next to."

When an interpreter seems to be making faces, these markers are often what you are seeing. They work together with other facial grammar, such as eyebrow positions that mark different types of questions. Dropping them can change the meaning of a sentence, which is why interpreters keep them even when they are not mouthing any English.

Why it varies between interpreters and languages

Sign languages are separate languages, and they differ in how heavily they use spoken-word mouthings. Linguists have described some European sign languages, German Sign Language among them, as using mouthings extensively. ASL, by comparison, relies more on mouth gestures. Within a single language, the amount of mouthing also changes with the setting and the people being served. An interpreter working with someone who prefers English-like signing may mouth much more than an interpreter working into ASL for a native signer.

The material for this guide included no measurements of how often interpreters mouth. Statements about frequency here are general descriptions from sign language linguistics, not figures.

What this means when interpreting happens over a webcam

Mouthings and mouth gestures are silent, so a microphone does not capture them. They reach the viewer only through video. In remote interpreting, or on any call with a signing participant, the face therefore needs to be as visible as the hands:

• Frame the camera so the signer's face, hands and upper body are all in view, with room for signs made out to the sides.
• Light the face from the front so mouth shapes are not lost in shadow or backlight.
• Check whether background blur, virtual backgrounds or auto-framing in the conferencing app clip or smear the hands or face, and turn those features off if they do.
• Pin or spotlight the interpreter where the app allows it, so small mouth movements stay readable.
• On a weak connection, conferencing apps may lower resolution or frame rate, which blurs fast hand and mouth movements. A stronger or wired connection helps.

The microphone matters for the spoken side of the conversation. It carries the hearing speaker's audio that the interpreter listens to, and the interpreter's own voice when they speak aloud what a deaf participant signs. Setup for those inputs depends on the specific webcam, operating system and conferencing app, so this guide does not cover it.