A prospective multi-centre study of the benefits of bilateral hearing aids

In this prospective study the benefits of a second hearing aid were evaluated objectively (functional tests) and subjectively (questionnaires). In addition, a battery of diagnostic tests (by headphones) was applied to determine whether the bilateral benefit could be predicted from a priori tests.

Diagnostic tests by headphones (binaural masking level difference, interaural time difference, and speech reception thresholds per ear) were conducted to focus on binaural functioning, and free-field tests were used for unilateral and bilateral hearing aids in the same participants to analyze differences in speech intelligibility and horizontal localization. The participants were recruited from the regular patients for hearing aid fitting in eight Audiological Centers. Eventually, 214 participants participated in this study. Each of these participants was fitted with two new hearing aids and started a trial period. Before the trial period the headphone tests were conducted, after the trial period the free-field tests were conducted with one and two hearing aids, and the participants completed a questionnaire.

In a number of respects bilaterally fitted hearing aids offered a benefit relative to unilaterally fitted hearing aids (the so-called bilateral benefit), both subjectively (questionnaire) and objectively (speech perception in noise and localization). However, we found large interindividual differences and not all differences were clinically relevant. The results of the diagnostic tests showed that it was not possible to predict the bilateral benefit from a priori information based on headphone tests. At the end of the trial period 93% of the participants preferred a bilateral fitting.