  A critical assumption of all current visual speech recognition systems is
that there are visual speech units called visemes which can be mapped to units
of acoustic speech, the phonemes. Despite there being a number of published
maps it is infrequent to see the effectiveness of these tested, particularly on
visual-only lip-reading (many works use audio-visual speech). Here we examine
120 mappings and consider if any are stable across talkers. We show a method
for devising maps based on phoneme confusions from an automated lip-reading
system, and we present new mappings that show improvements for individual
talkers.
