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Based on the current results, the inconsistent pattern of vocal duration development found previously can be reconciled when voice quality properties of vocalizations are taken into account. A nonlinear curve is evident when a broad corpus of infant vocalizations is used, whereas a narrow corpus containing predominantly modal vocalizations displays a linear trend. The results demonstrate the necessity of including nonmodal voice qualities in infant duration experiments so as to not overstate the linear nature of duration increases.

The duration of three infants' vocalisations were examined during a six-month longitudinal study. In contrast to most other infant research, this study included in its analysis all vocalisations including those deemed vegetative or those having nonmodal voice quality. All three infants produced vocalisations which decreased in duration in the initial months. However between the 3rd and 5th month a significant increase (p<0.001) in the duration of vocalisations was found (from mean 207ms to 431ms). When vocalisations were analysed using perceptual voice quality categories, all were found to have significant differences (p<0.05) in duration relative to modal voice. Nonmodal voice qualities showed initial decreases in duration before increasing in duration in later months. In contrast those vocalisations produced using modal voice showed a positive linear trend and had the greatest linear rate of change across the study. These findings highlight the importance of including a wide variety of infant vocalisations including those with nonmodal voice quality in infant linguistic developmental studies.

This study is an acoustic investigation of voice quality in Australian English. The speech of 33 Indigenous Australians (Aboriginal English speakers) is compared to that of 28 Anglo Australians [Mainstream Australian English (MAE) speakers] from two rural locations in Victoria. Analysis of F0 and H1*-H2* reveals that pitch and voice quality differ significantly for male speakers according to dialect and for female speakers according to location. This study highlights previously undescribed phonetic and sociophonetic variability in voice quality in Australian English.