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Neurale correlaten van luidheid: luidheidsadaptatie, luidheidsaangroei en luidheidsbalancering

Book - Dissertation

Current clinical practice requires active cooperation of the patient to individually fit a hearing device. The most important parameters for this fitting process are related to loudness. The aim of this PhD was to find neural correlates of loudness using 40-Hz auditory steady-state responses. These responses are auditory evoked potentials that can be measured fully objectively, non-invasively, and frequency-specifically in the electroencephalogram (EEG) using scalp electrodes. The use of neural correlates has potential for future objective, more automatic, and individualized fitting of hearing devices. More specifically, the project was divided into three parts: loudness adaptation, loudness growth, and loudness balancing. In the first part, two studies are described related to loudness adaptation. In chapter 2, we found that modulated stimuli that are commonly used to evoke auditory steady-state responses, are subject to loudness adaptation at low levels, high carrier frequencies, and for all modulation types, with more loudness adaptation for mixed modulation than for sinusoidal amplitude modulation. However, in chapter 3, we evoked 40-Hz auditory steady-state responses to the mixed-modulated stimuli that caused most of the loudness adaptation behaviorally, and found that response amplitudes remain stable over time. In the second part, we measured complete loudness growth functions with two behavioral loudness tasks as well as 40-Hz auditory steady-state response amplitude growth functions. Monaural loudness growth seemed to match well with 40-Hz auditory steady-state response amplitude growth functions in all groups of participants. In chapter 4, we investigated participants who hear acoustically, i.e., normal hearing and hearing-impaired participants. In chapter 5, we investigated participants who hear electrically with cochlear implants. In the third part, the focus was binaural loudness balancing. In chapter 6, the adaptive and adjustment procedure to measure binaural loudness balance were investigated. Both procedures yielded similar final loudness balanced results if the adjustment procedure was conducted twice, from opposite perceptual sides. In the last chapters, the use of 40-Hz auditory steady-state response amplitudes was investigated to predict the binaural loudness balance for normal-hearing participants (chapter 7), and participants with asymmetric hearing (chapter 8). The latter group consisted of participants with acoustical asymmetric hearing and participants with bimodal hearing, who hear electrically with a cochlear implant and acoustically in the non-implanted ear. While variability across participants was observed, median across-ear ratios at balanced levels were close to 1 for all groups of participants. In summary, loudness adaptation was not reflected by 40-Hz auditory steady-state responses, but the response amplitudes showed a correspondence to loudness growth and could predict the balanced loudness point in many participants, although variability across participants was found as well.
Publication year:2018
Accessibility:Open