Electric and acoustic harmonic integration predicts speech-in-noise performance in hybrid cochlear implant users

Bonnard D(1), Schwalje A(1), Gantz B(1), Choi I(2).

Author information:
(1)Department of Otolaryngology – Head and Neck Surgery, University of Iowa
Hospitals and Clinics, Iowa City, IA, USA.
(2)Department of Otolaryngology – Head and Neck Surgery, University of Iowa
Hospitals and Clinics, Iowa City, IA, USA; Department of Communication Sciences
and Disorders, University of Iowa, Iowa City, IA, USA. Electronic address:
.

BACKGROUND: Pitch perception of complex tones relies on place or temporal fine
structure-based mechanisms from resolved harmonics and the temporal envelope of
unresolved harmonics. Combining this information is essential for
speech-in-noise performance, as it allows segregation of a target speaker from
background noise. In hybrid cochlear implant (H-CI) users, low frequency
acoustic hearing should provide pitch from resolved harmonics while high
frequency electric hearing should provide temporal envelope pitch from
unresolved harmonics. How the acoustic and electric auditory inputs interact for
H-CI users is largely unknown. Harmonicity and inharmonicity are emergent
features of sound in which overtones are concordant or discordant with the
fundamental frequency. We hypothesized that some H-CI users would be able to
integrate acoustic and electric information for complex tone pitch perception,
and that this ability would be correlated with speech-in-noise performance. In
this study, we used perception of inharmonicity to demonstrate this integration.
METHODS: Fifteen H-CI users with only acoustic hearing below 500 Hz, only
electric hearing above 2 kHz, and more than 6 months CI experience, along with
eighteen normal hearing (NH) controls, were presented with harmonic and
inharmonic sounds. The stimulus was created with a low frequency component,
corresponding with the H-CI user’s acoustic hearing (fundamental frequency
between 125 and 174 Hz), and a high frequency component, corresponding with
electric hearing. Subjects were asked to identify the more inharmonic sound,
which requires the perceptual integration of the low and high components.
Speech-in-noise performance was tested in both groups using the California
Consonant Test (CCT), and perception of Consonant-Nucleus-Consonant (CNC) words
in quiet and AzBio sentences in noise were tested for the H-CI users.
RESULTS: Eight of the H-CI subjects (53%), and all of the NH subjects, scored
significantly above chance level for at least one subset of the inharmonicity
detection task. Inharmonicity detection ability, but not age or pure tone
average, predicted speech scores in a linear model. These results were
significantly correlated with speech scores in both quiet and noise for H-CI
users, but not with speech in noise performance for NH listeners. Musical
experience predicted inharmonicity detection ability, but did not predict speech
performance.
CONCLUSIONS: We demonstrate integration of acoustic and electric information in
H-CI users for complex pitch sensation. The correlation with speech scores in
H-CI users might be associated with the ability to segregate a target speaker
from background noise using the speaker’s fundamental frequency.

Copyright © 2018 Elsevier B.V. All rights reserved.

DOI: 10.1016/j.heares.2018.06.016
PMCID: PMC6205699
PMID: 29980380 [Indexed for MEDLINE]

Auteurs Bordeaux Neurocampus