Abstract
ObjectivesThis study examined musical sound quality (SQ) in adult cochlear implant (CI) recipients. The study goals were to determine: the number of channels needed for high levels of musical SQ overall and by musical genre; the impact of device and patient factors on musical SQ ratings; and the relationship between musical SQ, speech recognition, and speech SQ to relate these findings to measures frequently used in clinical protocols.MethodsTwenty-one post-lingually deafened adult CI recipients participated in this study. Electrode placement, including scalar location, average electrode-to-modiolus distance (), and angular insertion depth were determined by CT imaging using validated CI position analysis algorithms (e.g., Noble et al., 2013; Zhao et al., 2018, 2019). CI programs were created using 4–22 electrodes with equal spatial distribution of active electrodes across the array. Speech recognition, speech SQ, music perception via a frequency discrimination task, and musical SQ were acutely assessed for all electrode conditions. Musical SQ was assessed using pre-selected musical excerpts from a variety of musical genres.ResultsCI recipients demonstrated continuous improvement in qualitative judgments of musical SQ with up to 10 active electrodes. Participants with straight electrodes placed in scala tympani (ST) and pre-curved electrodes with higher variance reported higher levels of musical SQ; however, this relationship is believed to be driven by levels of musical experience as well as the potential for preoperative bias in device selection. Participants reported significant increases in musical SQ beyond four channels for all musical genres examined in the current study except for Hip Hop/Rap. After musical experience outliers were removed, there was no relationship between musical experience or frequency discrimination ability and musical SQ ratings. There was a weak, but significant correlation between qualitative ratings for speech stimuli presented in quiet and in noise and musical SQ.ConclusionModern CI recipients may need more channels for musical SQ than even required for asymptotic speech recognition or speech SQ. These findings may be used to provide clinical guidance for personalized expectations management of music appreciation depending on individual device and patient factors.
Highlights
The cochlear implant (CI) is the most successful sensory prosthetic device to date, yielding significant improvements in speech understanding (e.g., Holden et al, 2013) and quality of life (e.g., McRackan et al, 2017) for the majority of recipients
◦ Control of patient variables including musical experience and music selection familiarity is recommended for future studies
The straight electrode recipients did have greater musical experience than the other participants in this sample (see below), which is a likely contributor; further work is needed to better understand these preliminary findings
Summary
The cochlear implant (CI) is the most successful sensory prosthetic device to date, yielding significant improvements in speech understanding (e.g., Holden et al, 2013) and quality of life (e.g., McRackan et al, 2017) for the majority of recipients. Despite its success for restoration of auditory detection and speech recognition, music perception and appreciation remain major challenges for most CI recipients, due to a number of factors including poor pitch and timbre perception as well as reduced spectral resolution (e.g., Kang et al, 2009; Jung et al, 2012) as well as potential for poor auditory neural health. A discrete number of 5–10 independent channels may be available to these recipients for various speech and auditory measures, despite having up to 12–22 intracochlear electrodes (Fishman et al, 1997; Friesen et al, 2001, 2005) These previous studies were completed using older-generation speech coding strategies with patients implanted using more traumatic surgical approaches, unknown electrode placement, and stricter candidacy criteria. Electrode placement is especially critical as multiple studies have documented that the electrode–neural interface is rarely uniform along the array with distances ranging from 0 to 2 mm from the closest modiolar location (Davis et al, 2016) and 13% of implanted devices have extracochlear electrodes not referenced in the operative report (Holder et al, 2018a)
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