Viseme

A viseme is a representational unit used to classify speech sounds in the visual domain. The term viseme was introduced based on the interpretation of the phoneme as a basic unit of speech in the acoustic/auditory domain, (Fisher, 1968). This is, however, at variance with the accepted definition of the phoneme as the smallest structural unit that distinguishes meaning within a given language—as a cognitive abstraction that is not bound to any sensory modality.