The proposed project is designed to provide a theoretical model for the development of speech motor skills in infancy. It is proposed that there are three major landmarks of speech motor development in the first 15 months of life. These are: 1) the ability to control phonation in a non-distress context (cooing) with onset at 6 to 8 weeks; 2) the ability to alternate opening and closing of the vocal tract above the glottis (reduplicated babbling) with onset at 6 to 8 months and 3) the ability to impose a variety of pitch contours in an average fundamental frequency (Fo) range upon a succession of vowel-like (vocant) and consonant-like (closant) sounds (expressive jargon), with onset at 12 to 15 months. These landmarks reflect anatomic and physiologic changes taking place within the speech motor system. They appear in an invariant order and within a specific are range in normal infants. Other speech motor acquisitions take the form of elaboration of speech motor skills. Some elaborations follow specific sequences, e.g,. the acquisition of nonsonorant closants and of Fo in the normal pitch range. However, these sequences are not closely tied to specific age ranges and do not show a constant temporal relationship with respect to one another or to the major speech motor landmarks. Other elaborations result from new co-occurrences of acoustic-articulatory features, i.e., concatenation of different segment types in a superposition of one articulatory feature upon another and organization of segments or syllables within a variety of suprasegmental patterns. These hypotheses will be tested in a study of 34 normal infants to be audio and videorecorded under laboratory conditions. The procedures to be employed in data analysis are those of Fo extraction, analysis of formant frequencies of vowel-like sounds, and the coding of randomly selected vocalization samples by trained listeners. Statistical analyses will be designed to determine changes taking place in temporal patterning, Fo contour and the variety and complexity of segmental features employed by the infant. The information obtained will be helpful in developing clinical scales for the assessment of infant speech motor skills as well as for assessment of the proposed model for speech motor development.
| Stark, R E; Bernstein, L E; Demorest, M E (1993) Vocal communication in the first 18 months of life. J Speech Hear Res 36:548-58 |
