Coarticulation of Lip Rounding

We investigated the extent of coarticulation of lip rounding in selected speech strings. Meaningful sentences containing sequences of one to four consonants preceding the vowel /u/ were constructed, with word and syllable boundaries falling within the sequences in various ways. High-speed cinefluorographic films were taken of three subjects producing these sentences and measurements of lip protrusion were made from selected film frames. For most utterances, the lip rounding gesture began during the approach to the closure phase of the first consonant in the sequence, extending over as many as four consonants preceding /u/. Word and syllable boundaries within the sequences did not affect the amount or the starting points of protrusion. Generally, the tongue and, to a lesser extent, the lips failed to achieve target positions defined during prolonged articulation of /hu/. Our results are discussed in relation to various conceptual models of speech production. The data are consistent with models presuming phoneme-size input units as well as those involving some type of syllabic input units. Further studies of coarticulation, designed to differentiate between the two types of models, are suggested by these results.