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Infant vocalizations : a developmental analysis of selected prosodic features Hanford, Barbara M.


Non-crying utterances of six 5- to 16-week-old infants recorded in their home environments are analyzed spectrographically for fundamental frequency (F₀) and duration. Biographical and perceptual data are used qualitatively to suggest reasons for intra- and inter-subject variability. Three major statistical analyses were performed: (1) regressions of acoustic features on age, (2) relationship of F₀ and duration, and (3) contrasts of the child's fundamental frequency in different contexts. Not all regressions of acoustic features on chronological age were significant. However, two trends were evident: (1) exponential increase of duration on age and (2) linear increase of within-utterance range on age. With chronological age as a basis for analysis, inter-subject variability was noted even for these trends. Since neither development nor environment are completely uniform within or among children, developmental and social data might provide a firmer basis for analysis in future. The result that children of the same chronological age vocalized differently simply by number of utterances further supports the need for quantitative developmental and social data as analytical criteria. Analysis of fundamental frequency by duration generally showed that frequency range was dependent on amount of fluctuation and duration of utterance. A more complex analysis of the F₀-contour than can be provided spectrographically might yield more definitive information about this relationship. The child's vocal interaction with his environment was analyzed both qualitatively and quantitatively. A frequency count of the number of utterances in different contexts revealed that most children vocalized more when alone than in the presence of an object or person. Hotelling's T² tests of fundamental frequency in different contexts showed further that children did not alter the F₀-contour or within-utterance range of their vocalizations as a response to different objects or situations. However, the fact that twenty percent of the T² tests were significant -- particularly for the most advanced subject -- demonstrates that these children are at least capable of altering their fundamental frequency according to different situations during the early weeks of life. Further research is indicated in this as well as in the other areas. All trends noted in this study will have to be reviewed in the context of the larger project from which the present sample of six subjects was drawn.

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