Spectral and binaural loudness summation of equally loud narrowband signals in single-sided-deafness and bilateral cochlear implant users

Abstract

Recent studies on loudness perception of binaural broadband signals in hearing impaired listeners found large individual differences, suggesting the use of such signals in hearing aid fitting. Likewise, clinical cochlear implant (CI) fitting with narrowband/single-electrode signals might cause suboptimal loudness perception in bilateral and bimodal CI listeners. Here spectral and binaural loudness summation in normal hearing (NH) listeners, bilateral CI (biCI) users, and unilateral CI (uCI) users with normal hearing in the unaided ear was investigated to assess the relevance of binaural/bilateral fitting in CI users. To compare the three groups, categorical loudness scaling was performed for an equal categorical loudness noise (ECLN) consisting of the sum of six spectrally separated third-octave noises at equal loudness. The acoustical ECLN procedure was adapted to an equivalent procedure in the electrical domain using direct stimulation. To ensure the same broadband loudness in binaural measurements with simultaneous electrical and acoustical stimulation, a modified binaural ECLN was introduced and cross validated with self-adjusted loudness in a loudness balancing experiment. Results showed a higher (spectral) loudness summation of the six equally loud narrowband signals in the ECLN in CI compared to NH. Binaural loudness summation was found for all three listener groups (NH, uCI, and biCI). No increased binaural loudness summation could be found for the current uCI and biCI listeners compared to the NH group. In uCI loudness balancing between narrowband signals and single electrodes did not automatically result in a balanced loudness perception across ears, emphasizing the importance of binaural/bilateral fitting.

A model framework for simulating spatial hearing of bilateral cochlear implant users

“…(3) Extensions to predict bilateral speech intelligibility are possible by connecting the AN spike outputs to the backend processing stages of other purposes such as an automatic speech recognition system (e.g., [37,110,111]) or by replacing it with more abstract internal model representations (e.g., [115,116]). ( 4) Applications for predicting CI users' bilateral loudness perception (e.g., [117]) by combining, e.g., the AN fiber outputs with a physiologically-motivated binaural loudness model (e.g., [118]). (5) The electrical hearing of one side could be replaced with an acoustic hearing periphery (e.g., [40,45,119]) or by combining the electrical hearing with an acoustic hearing on the same side [110,120].…”