Phonetic and pragmatic characteristics of infant directed speech in Thai : a longitudinal study

Abstract

The speech of 6 Thai mothers as directed to their infants (Infant Directed Speech-IDS) was investigated longitudinally at five different infants' ages: newborn, 3 months, 6 months, 9 months, and 12 months and to adults (ADS) in natural home setting. This maternal speech was examined in two aspects: 1) the phonetic characteristics, specifically, the prosodic aspects-pitch, tempo, and loudness; and 2) the pragmatic characteristics, i.e., the speech acts. In terms of the phonetic characteristics, prosodic features were acoustically analyzed. They are fundamental frequency, frequency range, syllable duration, utterance duration, numbers of syllable per utterance, and intensity. Results of a comparison between IDS and ADS showed that IDS used higher fundamental frequency, greater frequency range, longer syllable duration, shorter utterance duration, and less numbers of syllable per utterance. Concerning the age-related changes of prosodic features, at newborn it was characterized by longer syllable duration, longer utterance duration, and less numbers of syllable per utterance. While at six months the use of higher pitch and larger pitch range was very dominating. By 12 months, most prosodic features were almost similar to those of ADS. The variations between the age groups in all aspects were statistically analyzed using the Analysis of Variance (ANOVA). It was found that every variation of the prosodic features investigated across age groups was statistically significant. In terms of pragmatic characteristics, there were 24 types of linguistic action verbs (LAVs) found. They are to inform, describe, explain, count, call, question, order, request, blame, warn, threaten, forbid, persuade, exclaim, sing, calm, comfort, praise, tease, complain, reflect in word, greet, give turn, and keep turn. These LAVs were classified into five major types of speech act verbs (SAVs): 1) assertives 2) questions 3) directives 4) expressives 5) interaction management. Expressives were found most at all ages except at 12 months. At 6 months, mothers used expressives the most. Among the expressives, to tease was found most. Assertives and directives were found most in IDS directed to the 12 months old. A higher percentage of questions was found used with the newborns and the 3 months old.