Longitudinal Analysis of /s/ and /ʃ/ Productions in Children 2 to 7 Years

The purpose of this study was to investigate the longitudinal development of the speech sounds /s/ and /ʃ/ in child speech, utilizing both acoustic and perceptual measures. Research on the development and acquisition of fricative sounds, /s/ and /ʃ/, have been well documented, with the recently published norms describing sibilant fricatives acquisition between the ages of 4-5 years. Previous research has utilized spectral moment analysis, a method of numerically describing acoustic speech information, to document production of sibilant fricatives, including developmental patterns. For the present study, speech samples were obtained from the Arizona Child Acoustic Database repository for four participants (2 male, 2 female). Longitudinal data were available between ages 2-7 years for these participants. Single word speech targets containing the target phonemes, /s/ and /ʃ/, were selected for both the acoustic and perceptual measures. Spectral moments were measured for each speech task at each age. Perceptual data included a rating of sound accuracy for word initial and word final /s/. The four spectral moments indicated no significant stabilization of sibilant fricative production as a function of age. The findings of the perceptual component of this study are that children’s productions of /s/ gradually improve in accuracy with age, stabilizing with high accuracy ratings around five years. This finding is consistent with previous research that suggests a “fine-tuning” of speech production with development. Several suggestions for future research are identified, including the use of different acoustic measures, such as frication duration, to acoustically characterize the longitudinal development of sibilant fricatives in child speech