Objectives:
Building on the concept that task type may influence fundamental frequency (F(0)) values, the purpose of this case study was to investigate the difference in a child's F(0) during structured, elicited tasks and long-term, unstructured activities. It also explores the possibility that the distribution in children's F(0) may make the standard statistical measures of mean and standard deviation less than ideal metrics.
Methods:
A healthy male child (5 years, 7 months) was evaluated. The child completed four voice tasks used in a previous study of the influence of task type on F(0) values: (1) sustaining the vowel /a/ in isolation; (2) sustaining the vowel /a/ embedded in a word at the end of a phrase; (3) repeating a sentence; and (4) counting from 1 to 10. The child also wore a National Center for Voice and Speech voice dosimeter, a device that collects voice data over the course of an entire day, during all activities for 34 h over 4 days.
Results:
Throughout the structured vocal tasks within the clinical environment, the child's F(0), as measured by both the dosimeter and acoustic analysis of microphone data, was similar for all four tasks, with the counting task the most dissimilar. The mean F(0) (approximately 257 Hz) matched very closely to the average task results in the literature given for the child's age group. However, the child's mean fundamental frequency during the unstructured activities was significantly higher (approximately 376 Hz). Finally, the mode and median of the structured vocal tasks were 260 Hz and 259 Hz respectively (both near the mean), while the unstructured mode and median were 290 Hz and 355 Hz respectively.
Conclusions:
The results of this study suggest that children may produce a notably different voice pattern during clinical observations compared to routine daily activities. In addition, the child's long-term F(0) distribution is not normal. If this distribution is consistent in long-term, unstructured natural vocalization patterns of children, statistical mean would not be a valid measure. Mode and median are suggested as two parameters which convey more accurate information about typical F(0) usage. Finally, future research avenues, including further exploration of how children may adapt their F(0) to various environments, conversation partners, and activity, are suggested.