Tonal confusions in Thai patients with sensorineural hearing loss

In a tone language, every syllable or word may have a distinctive pitch pattern as part of its phonemic composition. This study examined the extent and nature of impairment in the perception of phonemic tones by hearing-impaired listeners in Thai, a tone language that has five phonemic tones. Seventy-six subjects were assigned to four listener groups: normal-hearing (n = 21), mild-hearing-loss (n = 21), moderate-hearing-loss (n = 26), and severe-hearing-loss (n = 8). Five Thai words differing only in tone were presented for identification in both natural speech and synthetic speech versions. Results from the phonemic identification tests indicated that tonal identification is affected by the presence of sensorineural hearing loss. In particular, the number and often the type of tonal confusions made by Thai hearing-impaired listeners varied with the extent of hearing loss for both natural and synthetic speech versions. In contrast to previous findings on the patterns of consonant and vowel confusions in hearing-impaired listeners, the patterns of tonal confusions in hearing-impaired listeners can be related to the degree of hearing loss.