Optimal gain control step sizes for bimodal stimulation

Abstract

Objective: Cochlear implants (CI) and hearing aids (HA) have a gain control that allows the bimodal user to change the loudness. Due to differences in dynamic range between CI and HA, an equal change of the gains of the two devices results in different changes in loudness. The objective was to relate and individualise the step sizes of the loudness controls to obtain a similar perceptual effect in the two ears. Design: We used loudness models parametrised for individual users to find a relation between the controls of the CI and the HA such that each step resulted in an equal change in loudness. We conducted loudness balancing experiments to validate the results. Study sample: Eleven bimodal users of whom six were tested in a prior study. Results: The difference between the optimal gain from the loudness balancing procedure and actual gain was 3.3 dB when the new relation was applied. In contrast, the difference was 8 dB if equal step sized were applied at both sides. Conclusion: We can relate the controls such that each step results in a similar loudness difference.

Key Words:

• Cochlear implant
• hearing aid
• bimodal
• gain settings
• loudness models

Acknowledgements

We thank Maaike Van Eeckhoutte and Camille Simons for the support in data acquisition and the participants recruitment. Lieselot Van Deun provided valuable feedback on this manuscript. We also thank Professor Robert Cowan and the two anonymous reviewers for their constructive remarks to improve the manuscript. Finally, we are grateful to the bimodal users who voluntarily participated in the experiments.

Declaration of interest

Bas van Dijk is an employee of Cochlear Technology Centre Belgium. The rest of the authors report no declaration of interest.

We would like to acknowledge the support from Flanders Innovation [IWT R&D 110722 and IWT Baekeland 140748]. Cochlear Ltd also provided financial support and the necessary additional equipment.

Notes

 1. The models do not account for frequency mismatches between the electrical and acoustical stimulation and the resulting (lack of) fusion, so our method may be improved using more sophisticated models that take this into account.