BILATERAL HEARING AIDS FOR BILATERALLY HEARING-IMPAIRED PERSONS - ALWAYS THE BEST CHOICE?

The most logical solution if a person has a hearing impairment on both ears, seems to be bilateral hearing aid amplification in both ears. Numerous studies have shown the advantages of this fitting strategy. However, there were always some individuals not benefiting from bilateral hearing aids; until recently a neglected group of persons. The first part of the present work examines patterns of usage of bilateral hearing aids and situations where the users benefit most from bilateral hearing aids. Measurements of speech recognition in noise and localization with two, one and no hearing aids were performed. The second part of this work concentrates on persons rejecting bilateral hearing aids because of unspecified reasons, not related to practical or technical issues. Paper I describes an enquiry-based, retrospective study with questions on experienced advantages and disadvantages of bilateral hearing aids as well as the pattern in which the hearing aids were used. A majority of the 144 persons participating in the survey used bilateral hearing aids. Two hearing aids were mainly appreciated in complex listening situations with high demands on speech recognition. Improved sound quality was one of the reasons to use two rather than one hearing aid. The users of two hearing aids described better localization abilities than users of one hearing aid. In the second study, paper II, 19 bilaterally hearing-impaired persons, provided with two hearing aids, participated in psychoacoustical measurements of speech recognition in noise and localization. Both measurements showed an advantage for bilateral hearing aids. Localization could not be improved beyond the score, that the participants reached without hearing aids, but the level of localization could at least be retained with two hearing aids whereas it deteriorated with a unilateral hearing aid. In the study described in paper III, methods to measure individual auditory performance with focus on binaural aspects of the auditory system were put together. An evaluation with normalhearing subjects showed significantly different results for measurements of speech recognition in noise and signal analysis abilities under monaural and binaural listening conditions. A measurement of central auditory and cognitive function also was included in this evaluation. The final step of this work, paper IV, was the application of the methods developed in paper III on two groups of hearing-impaired persons, one group appreciating bilateral hearing aids, one group rejecting them and using unilateral amplification instead. The study had a diagnostic approach with all measurements performed unaided. Significant differences between the two groups were found in central auditory performance and cognition with an advantage for the group benefiting from bilateral hearing aids. To a less degree, also peripheral hearing might be degraded in the group preferring one hearing aid and they also might have been provided with too much amplification in their hearing aids. The binaural performance was about the same in both groups. This work has shown, in which situations it is advantageous to use bilateral hearing aids. Tests have been identified to provide better understanding and diagnostic possibilities for hearingimpaired persons, who are not able to benefit from bilateral amplification.