Effects of Hearing Loss on School-Aged Children's Ability to Benefit From F0 Differences Between Target and Masker Speech.

Abstract

The objectives of the study were to (1) evaluate the impact of hearing loss on children's ability to benefit from F0 differences between target/masker speech in the context of aided speech-in-speech recognition and (2) to determine whether compromised F0 discrimination associated with hearing loss predicts F0 benefit in individual children. We hypothesized that children wearing appropriately fitted amplification would benefit from F0 differences, but they would not show the same magnitude of benefit as children with normal hearing. Reduced audibility and poor suprathreshold encoding that degrades frequency discrimination were expected to impair children's ability to segregate talkers based on F0. Listeners were 9 to 17 year olds with bilateral, symmetrical, sensorineural hearing loss ranging in degree from mild to severe. A four-alternative, forced-choice procedure was used to estimate thresholds for disyllabic word recognition in a 60-dB-SPL two-talker masker. The same male talker produced target and masker speech. Target words had either the same mean F0 as the masker or were digitally shifted higher than the masker by three, six, or nine semitones. The F0 benefit was defined as the difference in thresholds between the shifted-F0 conditions and the unshifted-F0 condition. Thresholds for discriminating F0 were also measured, using a three-alternative, three-interval forced choice procedure, to determine whether compromised sensitivity to F0 differences due to hearing loss would predict children's ability to benefit from F0. Testing was performed in the sound field, and all children wore their personal hearing aids at user settings. Children with hearing loss benefited from an F0 difference of nine semitones between target words and masker speech, with older children generally benefitting more than younger children. Some children benefitted from an F0 difference of six semitones, but this was not consistent across listeners. Thresholds for discriminating F0 improved with increasing age and predicted F0 benefit in the nine-semitone condition. An exploratory analysis indicated that F0 benefit was not significantly correlated with the four-frequency pure-tone average (0.5, 1, 2, and 4 kHz), aided audibility, or consistency of daily hearing aid use, although there was a trend for an association with the low-frequency pure-tone average (0.25 and 0.5 kHz). Comparisons of the present data to our previous study of children with normal hearing demonstrated that children with hearing loss benefitted less than children with normal hearing for the F0 differences tested. The results demonstrate that children with mild-to-severe hearing loss who wear hearing aids benefit from relatively large F0 differences between target and masker speech during aided speech-in-speech recognition. The size of the benefit increases with increasing age, consistent with previously reported age effects for children with normal hearing. However, hearing loss reduces children's ability to capitalize on F0 differences between talkers. Audibility alone does not appear to be responsible for this effect; aided audibility and degree of loss were not primary predictors of performance. The ability to benefit from F0 differences may be limited by immature central processing or aspects of peripheral encoding that are not characterized in standard clinical assessments.