The Effect of Stimulus Bandwidth on Perception of Fricative /s/ among Individuals with Different Degrees of Sensorineural Hearing Loss

Abstract

Most of the speech sounds that contribute to speech intelligibility are dominated by high-frequency components. The phoneme /s/ is the third or fourth most frequently occurring phoneme in the English language and second most frequently occurring consonantal phoneme in Hindi language. Given the importance of the phoneme /s/, it is ironic that, this sound contains the highest frequency acoustic elements of any speech sound in English and most of the non-English languages ranging from 4500 Hz to more than 8000 Hz. The most common type of hearing impairment affecting speech perception is high-frequency sensorineural loss (SN) and such individuals require good high frequency audibility in order to better perceive fricative cues, regardless of hearing status. While many studies appear to support the general notion that high-frequency amplification may not always be beneficial, the inter-subject variability in most studies precludes a clearly defined rule that would distinguish listeners who are likely to benefit from high-frequency amplification from those who are not. The current study is aimed to determine and compare the effective bandwidth required for the perception of fricative /s/ in individuals with normal hearing and hearing impairment as a function of degree of hearing loss. A total of 100 Hindi speaking subjects equally divided into four groups (Group I: Normal hearing, Group II: Moderate SN hearing loss, Group III: Moderately severe SN hearing loss, Group IV: Severe SN hearing loss) participated in the study. Nonsense syllables containing the phonemes /s/, /f/, /ṣ/ and /c/ in /i/ vowel context and low pass filtered at 1, 2, 3, 4, 5, 6, 7, 8 and 9 KHz produced by a female talker were used as stimulus. The results revealed that there was a statistically significant effect (p 0.05) was seen at 9 KHz between groups. In addition, individuals with normal hearing required lower bandwidth for accurate fricative perception and there was a statistically significant difference (p<0.05) in mean bandwidth between groups. Among the hearing impaired group, as the degree of hearing loss increased the subjects required higher bandwidth for accurate perception of fricative. This study has important implications in knowing the effective bandwidth required for the perception of high frequency speech sounds among individuals with hearing loss on individual basis which in turn helps in the selection of appropriate rehabilitative devices.