Lip reading

Lip reading, also known as lipreading or speechreading, is a technique of understanding speech by visually interpreting the movements of the lips, face and tongue when normal sound is not available, relying also on information provided by the context, knowledge of the language, and any residual hearing. Although primarily used by deaf and hard-of-hearing people, people with normal hearing generally process visual information from the moving mouth at a subconscious level.

Process

In everyday conversation, people with normal vision, hearing and social skills sub-consciously use information from the lips and face to aid aural comprehension and most fluent speakers of a language are able to speechread to some extent (see McGurk effect). This is because each speech sound (phoneme) has a particular facial and mouth position (viseme), and people can to some extent deduce what phoneme has been produced based on visual cues, even if the sound is unavailable or degraded (e.g. by background noise).