Introduction: Clinically, the audiogram is the most commonly used measure when evaluating hearing loss and fitting hearing aids. As an extension, we present the loudness audiogram, which does not only show auditory thresholds but also visualises the full course of loudness perception. Methods: In a group of 15 bimodal users, loudness growth was measured with the cochlear implant and hearing aid separately using a loudness scaling procedure. Loudness growth curves were constructed, using a novel loudness function, for each modality and then integrated in a graph plotting frequency, stimulus intensity level, and loudness perception. Bimodal benefit, defined as the difference between wearing a cochlear implant and hearing aid together versus wearing only a cochlear implant, was assessed for multiple speech outcomes. Results: Loudness growth was related to bimodal benefit for speech understanding in noise and to some aspects of speech quality. No correlations between loudness and speech in quiet were found. Patients who had predominantly unequal loudness input from the hearing aid, gained more bimodal benefit for speech understanding in noise compared to those patients whose hearing aid provided mainly equivalent input. Discussion: Fitting the cochlear implant and a contralateral hearing aid to create equal loudness at all frequencies may not always be beneficial for speech understanding.

The authors have declared no competing interest.

Dutch National Trial Register (NTR3932)

A research grant from Advanced Bionics Inc. to Maastricht University Medical Centre (MUMC+) financially supported the work of the first (Lars Lambriks) and last author (Elke Devocht) in this investigator-initiated study. The funder had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

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This study has been approved by the ethics committee of the Maastricht University Medical Center (MUMC+) under registration number NL42011.068.13 and has been registered in the Dutch National Trial Register (NTR3932). Subjects provided written informed consent before participation and were compensated for their travelling costs.

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