A viseme is any of several speech sounds that look the same, for example when lip reading (Fisher 1968).

Each dominance function represents the influence over time that a viseme has on a speech utterance.

The viseme shapes were sampled from syllables uttered by the babies on the set.

Speechreading is limited, however, in that many phonemes share the same viseme and thus are impossible to distinguish from visual information alone.

The source of this variation is termed coarticulation which is the influence of surrounding visemes upon the current viseme (i.e. the effect of context).

Typically the influence will be greatest at the center of the viseme and will degrade with distance from the viseme center.

Confusability of Phonemes Grouped According to their Viseme Classes in Noisy Environments"."

To account for coarticulation current systems either explicitly take into account context when blending viseme keyframes or use longer units such as diphone, triphone, syllable or even word and sentence-length units.

As the basis units already incorporate the variation of each viseme according to context and to some degree the dynamics of each viseme, no model of coarticulation is required.

Lip-reading football speak is a precarious occupation after the debacle over Marco Materazzi’s comments to Zinédine Zidane during the 2006 World Cup final, when the world’s professional interpreters of phoneme and viseme came up with so many versions of what was said as to render the process ridiculous.