Individual variation in the realisation and contrast of Swedish children’s word-initial voiceless fricatives

In this study, we explore individual variation and contrast in Swedish children's voiceless fricatives. Thirty-one children between three and eight years of age participated in a picture-prompted word repetition task, wherein they repeated fricative-initial words in a variety of vowel contexts. The fricatives were transcribed and acoustically analysed, using spectral moments 1–4, spectral peak and spectral balance measures. Random forests were used to estimate the relative importance of each spectral feature in the classification of correct fricative productions, as well as to measure robustness of the late-emerging contrast between sibilants s and ɕ in individual children. Transcription analysis revealed that substitutions involving a more anterior place of articulation were common. Acoustic analysis showed individual differences in variability and contrast in the children's fricative systems across and within age groups. Cue weighting of spectral characteristics in classification was similar in all age groups for correct productions, while the magnitude of the acoustic contrast between sibilants increased with age. This paper provides a description of individual variation in Swedish children's acquisition of fricatives which can inform future large-scale speech-acquisition research.