Comprehension Test of Japanese and English Using Deaf Filters: Candidacy Criteria of EAS in Japanese Language Speaking Patients

Objective: The audiometric criteria for electric acoustic stimulation (EAS) is now universally defined in the USA and European countries as a mild to moderate low frequency sensorineural hearing loss (within 60–65 dB at 125, 250, and 500 Hz) sloping to a profound hearing loss in the higher frequencies. However, Japanese language is thought to have more importance in the lower frequency range compared to English. We therefore investigated whether the audiometric threshold criteria should be changed or not according to language specifications.<br> Methods: We designed a comprehension test of Japanese and English using experimentally designed deaf filters with residual hearing in the low frequencies. The test sentences were on a CD, which was played to the subjects at 60 dB SPL in the free field via four designed deaf filters in the lower frequencies. The scores of CID sentence scores (English) and CI-2004 (Japanese) were assessed. There were 8 normal hearing subjects who were bilingual in Japanese and American English. Both test sentences were given to the same subjects consecutively.<br> Results: The speech comprehension scores were much better in Japanese CI-2004 compared with in English CID. The data from the two groups were statistically analyzed using the paired t-test and the result showed that the mean scores were significantly different (p<0.01 or 0.005) using filters 1, 2, and 3. The distribution of scores was also much wider in Japanese CI-2004.<br> Conclusion: Japanese language contains more vowels and gliding consonant sounds (=semivowels) in sentences and has more importance in the lower frequency range compared to English. In addition, the personal equation in Japanese sentence recognition is also larger. Therefore, the audiometric threshold criteria should be changed and the proper guidelines including not only a monosyllabic test but a sentence comprehension test should be added according to the language specifications for EAS cochlear implantation.<br>