Abstract
Conclusion In users of a cochlear implant (CI) and a hearing aid (HA) in contralateral ears, frequency-dependent loudness balancing between devices did, on average, not lead to improved speech understanding as compared to broadband balancing. However, nine out of 15 bimodal subjects showed significantly better speech understanding with either one of the fittings. Objectives Sub-optimal fittings and mismatches in loudness are possible explanations for the large individual differences seen in listeners using bimodal stimulation. Methods HA gain was adjusted for soft and loud input sounds in three frequency bands (0–548, 548–1000, and >1000 Hz) to match loudness with the CI. This procedure was compared to a simple broadband balancing procedure that reflected current clinical practice. In a three-visit cross-over design with 4 weeks between sessions, speech understanding was tested in quiet and in noise and questionnaires were administered to assess benefit in real world. Results Both procedures resulted in comparable HA gains. For speech in noise, a marginal bimodal benefit of 0.3 ± 4 dB was found, with large differences between subjects and spatial configurations. Speech understanding in quiet and in noise did not differ between the two loudness balancing procedures.
Highlights
Beneficial effects for the combined use of a cochlear implant (CI) and a contralateral hearing aid (HA) have repeatedly been reported [1]
We aimed at the more modest goal of achieving balanced loudness between both ears considering that, even if true loudness normalization cannot be achieved, the brain may still be plastic enough to extract binaural cues if loudness is balanced across input levels and frequencies [6]
We investigated the effect of loudness balancing in three separate frequency bands: (1) low frequencies up to 500 Hz that contain voicing cues and complement information provided by the CI; (2) the middle frequency band (500 Hz–1 kHz) that potentially contains segmental
Summary
Beneficial effects for the combined use of a cochlear implant (CI) and a contralateral hearing aid (HA) have repeatedly been reported [1]. Advantages provided through such ‘bimodal’ stimulation can include improved speech understanding in noise, voice pitch perception, localization abilities, and music perception [2,3,4]. The factors that underlie these differences are not fully investigated, but may include, for example, tonotopical mismatches, degree of hearing loss and binaural fusion, sub-optimal fittings, and mismatches in loudness. An essential part of fitting is to obtain equal loudness percepts at both ears, but no well-validated bimodal fitting procedure is available to achieve this. We aimed at the more modest goal of achieving balanced loudness between both ears considering that, even if true loudness normalization cannot be achieved, the brain may still be plastic enough to extract binaural cues if loudness is balanced across input levels and frequencies [6]
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