  Visual lip gestures observed whilst lipreading have a few working
definitions, the most common two are; `the visual equivalent of a phoneme' and
`phonemes which are indistinguishable on the lips'. To date there is no formal
definition, in part because to date we have not established a two-way
relationship or mapping between visemes and phonemes. Some evidence suggests
that visual speech is highly dependent upon the speaker. So here, we use a
phoneme-clustering method to form new phoneme-to-viseme maps for both
individual and multiple speakers. We test these phoneme to viseme maps to
examine how similarly speakers talk visually and we use signed rank tests to
measure the distance between individuals. We conclude that broadly speaking,
speakers have the same repertoire of mouth gestures, where they differ is in
the use of the gestures.
