The benefits of bilateral versus unilateral amplification for the elderly: are two always better than one?

The use of bilateral hearing aids is based on the assumption that the human auditory system functions best when both ears receive incoming acoustic information. There is evidence, however, that some elderly individuals perform better while using unilateral as opposed to bilateral amplification. The main objective of the present study was to compare speech recognition in noise in elderly hearing-impaired patients initially fitted with bilateral hearing aids while they used unilateral versus bilateral amplification. A secondary goal was to investigate the association between performance with one versus two hearing aids and central auditory function as measured by a dichotic test, and to evaluate the effect of increasing age on these two measures. Twenty-eight patients (mean age 72.8 years, range: 62-86) with bilateral symmetrical mild-to-severe sensorineural hearing loss fitted with digital hearing aids, participated in the study. Speech recognition in noise was assessed in three conditions: (1) aided right ear, (2) aided left ear, (3) aided bilaterally, using the AB open-set monosyllabic word test at a signal-to-noise ratio of +10 dB. Speech stimuli were presented at 70 dB SPL via a loudspeaker located at 0 degree azimuth and the noise was presented via a second loudspeaker located at 180 degrees azimuth. In addition, dichotic listening abilities were evaluated using the threshold-of-interference test. The results of the present study indicated comparable mean group performance while using unilateral versus bilateral amplification. For the most of the patients (71%), however, speech recognition in noise was better while using unilateral amplification to the 'better' ear compared to bilateral amplification. While the performance in the dichotic test was not correlated with speech recognition in noise with bilateral versus unilateral amplification, the performance in these two tests deteriorated significantly with increasing age. Our results suggest that for elderly patients, bilateral amplification may not always be advantageous for speech recognition in noise. As most patients continue to use bilateral amplification, it is clear that there are listening situations in which bilateral amplification provides benefit. Sensitive performance measures that will tap critical aspects of daily binaural listening situations are therefore required. Finally, the deterioration in performance of the aging auditory system underscores the need to 'tailor' auditory habilitation to individual needs.