Audio-visual interaction (1)
For multimedia applications that involve person to person conversation (i.e., video telephony, video conferencing) , such interaction is particularly significant, because human speech is bimodal in nature.
Parallel to the basic unit of acoustic speech, i.e., the phoneme, in the visual domain, we have the notion of viseme, i.e., the basic unit of mouth movements that constitutes a visibly distinguishable unit of speech.
The acoustic and visual components of the speech signal are not purely redundant; they are complementary as well.