Abstract
OBJECTIVES: At poor signal-to-noise ratios, speech understanding may depend on the ability to combine speech fragments that are distributed across time and frequency. The goal of this study was to determine the effects of development and hearing impairment on this ability. DESIGN: Listeners in the present study included adults and children with normal hearing and with hearing impairment. The children with normal hearing included a younger group (aged 4.6-6.9 yr, N = 10) and an older group (aged 7.3-11.1 yr, N = 11). The adults with normal hearing were aged 19 to 27 yr (N = 10). Adults (aged 19-54 yr, N = 9) and children (aged 7.2-10.7 yr, N = 8) with hearing impairment were also tested. The two groups with hearing impairment had comparable mild/moderate bilateral sensorineural hearing impairment. Masked speech reception thresholds for sentences were determined in a baseline condition of steady speech-shaped noise and in noise that was temporally modulated, spectrally modulated, or both temporally and spectrally modulated. RESULTS: The results of normal-hearing listeners indicated higher masked speech reception thresholds for children than adults in steady noise. Adults and children showed the same magnitude of masking release for spectral modulation. Adults showed more masking release than the younger children for temporal modulation and showed more masking release than both the younger and older children for combined temporal/spectral modulation. Comparing normal-hearing and hearing-impaired listeners, the hearing-impaired listeners had higher masked speech reception thresholds in the steady noise condition and reduced masking release in the modulated noise conditions. Neither the two-way interaction between age and hearing impairment nor the three-way interaction between age, hearing impairment, and masking configuration was significant. CONCLUSIONS: Although the reduced masking release for temporal modulation shown by the younger children with normal hearing could be a result of poor temporal resolution, it more likely reflects inefficient use of speech cues in temporal gaps or factors stemming from higher signal-to-noise ratios required by children in the baseline condition. The reduced masking release for combined temporal/spectral modulation demonstrated by both the younger and older children with normal hearing may indicate that children in the age range tested here have some difficulty in combining speech information that is distributed across temporal and spectral gaps. Hearing impairment was associated with higher thresholds and reduced masking release in all modulation conditions. Children with hearing impairment showed the poorest performance of any group, consistent with additive effects of hearing loss and development.