Bandwidth effects on children's perception of the inflectional morpheme /s/: acoustical measurements, auditory detection, and clarity rating.

The goal of this study was to examine developmental effects in auditory perception of word-final /s/ in inflectional morpheme contexts as a function of high-frequency (HF) bandwidth. Such developmental effects may support the use of hearing aids with extended bandwidths in young children with impaired hearing. The first part of the study consisted of acoustical measurements on word-initial /s/ and inflectional morpheme /s/ in sentences recorded from a male speaker. For this speaker, recordings of inflectional morpheme /s/ on average were approximately 50 ms shorter and about 5 dB lower in level than word-initial /s/ sounds. They also had a lower spectral center of gravity, but not a higher coefficient of kurtosis. The second part consisted of measurements of psychometric functions relating detection of the inflectional morpheme /s/ sounds to HF bandwidth in normally hearing 5-, 7-, and 10-year-old children and adults. In speech-shaped noise, significant main effects of age were found for detection as a function of bandwidth for both the 30- and 10-dB signal-to-noise ratio (SNR) condition, although there was no interaction between age and SNR condition. The third part consisted of subjective clarity rating as a function of HF bandwidth for the same speech stimuli used in the second part. No differences were found between age groups in the shape of the clarity rating functions, but differences were found in the rating variance. No systematic effects of the spectral composition of inflectional morpheme /s/ sounds on either detection or clarity rating were found. The higher detection thresholds and larger clarity rating variances for the youngest participants support the use of extended high-frequency bandwidths for young children with impaired hearing. The extent to which the potential benefit of extended bandwidths is affected by hearing impairment in this population, however, deserves further investigation.