Objective Binaural Loudness Balancing Based on 40-Hz Auditory Steady-State Responses. Part II: Asymmetric and Bimodal Hearing

Abstract

In Part I, we investigated 40-Hz auditory steady-state response (ASSR) amplitudes for the use of objective loudness balancing across the ears for normal-hearing participants and found median across-ear ratios in ASSR amplitudes close to 1. In this part, we further investigated whether the ASSR can be used to estimate binaural loudness balance for listeners with asymmetric hearing, for whom binaural loudness balancing is of particular interest. We tested participants with asymmetric hearing and participants with bimodal hearing, who hear with electrical stimulation through a cochlear implant (CI) in one ear and with acoustical stimulation in the other ear. Behavioral loudness balancing was performed at different percentages of the dynamic range. Acoustical carrier frequencies were 500, 1000, or 2000 Hz, and CI channels were stimulated in apical or middle regions in the cochlea. For both groups, the ASSR amplitudes at balanced loudness levels were similar for the two ears, with median ratios between left and right ear stimulation close to 1. However, individual variability was observed. For participants with asymmetric hearing loss, the difference between the behavioral balanced levels and the ASSR-predicted balanced levels was smaller than 10 dB in 50% and 56% of cases, for 500 Hz and 2000 Hz, respectively. For bimodal listeners, these percentages were 89% and 60%. Apical CI channels yielded significantly better results (median difference near 0 dB) than middle CI channels, which had a median difference of −7.25 dB.

Cortical auditory evoked potential in cochlear implant users: An objective method to improve speech perception

“…For instance, a CI is programmed through measuring the lowest current stimulation level that a patient can hear consistently (T levels) and the maximum comfortable level (C or MCL). MCLs are set with a minimal amount of current stimulation and gradually increased until the patient reports the sound is "loud but comfortable", thereby creating an electrical dynamic range (DR) for each CI electrode [3]. However, this programming method is not standardized, with techniques varying widely both between individual clinicians and between CI clinics [4,5].…”

Improved binaural speech reception thresholds through small symmetrical separation of speech and noise

“…In their recent cohort study, Hoppe et al [ 13 ] showed that hearing performance in aided hearing-impaired listeners can typically be considered as asymmetrical. Against this background [ 33 , 34 ], a quantification of binaural hearing is needed for evaluation of the treatment. Numerous approaches have attempted to assess hearing performance in asymmetrical hearing conditions.…”

Considerations for Fitting Cochlear Implants Bimodally and to the Single-Sided Deaf

“…Various behavioral and evoked-response based measurements have been suggested to derive the interaural level mismatch in CI users ( Balkenhol et al, 2020 ). Most commonly “loudness balancing” is the reported fitting goal and as such also the mismatch measurement technique ( van Eeckhoutte et al, 2018 ; Veugen et al, 2016a ). However, just because this term is used does not mean that loudness balancing was actually performed (see section “causes of level mismatch”).…”

“…A very different approach is to use evoked, response-related measurements, allowing level estimates and balancing at specific stages of the auditory pathway, for example in the brainstem and midbrain by means of auditory brainstem response (ABR) amplitudes ( van Eeckhoutte et al, 2018 ) or late auditory evoked potentials (LAEP), which are more strongly correlated with loudness ( Hoppe et al, 2001 ). Similar to the loudness-scaling procedure, obtaining level-mismatch data via evoked-response-related measures is highly time consuming.…”