Interaural Pitch-Discrimination Range Effects for Bilateral and Single-Sided-Deafness Cochlear-Implant Users
By allowing bilateral access to sound, bilateral cochlear implants (BI-CIs) or unilateral CIs for individuals with single-sided deafness (SSD; i.e., normal or near-normal hearing in one ear) can improve sound localization and speech understanding in noise. Spatial hearing in the horizontal plane is primarily conveyed by interaural time and level differences computed from neurons in the superior olivary complex that receive frequency-matched inputs. Because BI-CIs and SSD-CIs do not necessarily convey frequency-matched information, it is critical to understand how to align the inputs to CI users. Previous studies show that interaural pitch discrimination for SSD-CI listeners is highly susceptible to contextual biases, questioning its utility for establishing interaural frequency alignment. Here, we replicate this finding for SSD-CI listeners and show that these biases also extend to BI-CI listeners. To assess the testing-range bias, three ranges of comparison electrodes (BI-CI) or pure-tone frequencies (SSD-CI) were tested: full range, apical/lower half, or basal/upper half. To assess the reference bias, the reference electrode was either held fixed throughout a testing block or randomly chosen from three electrodes (basal end, middle, or apical end of the array). Results showed no effect of reference electrode randomization, but a large testing range bias; changing the center of the testing-rage shifted the pitch match by an average 63 % (BI-CI) or 43 % (SSD-CI) of the change magnitude. This bias diminished pitch-match accuracy, with a change in reference electrode shifting the pitch match only an average 34 % (BI-CI) or 40 % (SSD-CI) of the expected amount. Because these effects extended to the relatively more symmetric BI-CI listeners, the results suggest that the bias cannot be attributed to interaural asymmetry. Unless the range effect can be minimized or accounted for, a pitch-discrimination task will produce interaural place-of-stimulation estimates that are highly influenced by the conditions tested, rather than reflecting a true interaural place-pitch comparison.
Keywordscochlear implant pitch binaural hearing interaural mismatch
We thank Cochlear Ltd. and Med-El for providing the testing equipment and technical support. We thank Danielle King, Emily Waddington, and Tori Levi who helped collect data for this study. We thank the Department of Hearing and Speech Sciences at University of Maryland, College Park (Dr. Nicole Nguyen), the Cochlear Implant Center at Greater Baltimore Medical Center (Dr. Regina Presley), the University of Maryland Medical School (Dr. David Eisenman and Dr. Ronna Hertzano), and Walter Reed National Military Medical Center (Dr. Gerald Schuchman) for their assistance with recruiting listeners. We thank Ginny Alexander for the managerial help and Kenneth Jensen for helpful comments on a previous version of this paper. The views expressed in this article are those of the authors and do not reflect the official policy of the Department of Army/Navy/Air Force, Department of Defense, or U.S. Government. The identification of specific products or scientific instrumentation does not constitute endorsement or implied endorsement on the part of the author, DoD, or any component agency.
The research reported in this publication was supported by the National Institute On Deafness And Other Communication Disorders of the National Institutes of Health under Award Number R01 DC015798 (M.J.G. and J.G.W.B.). The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.
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Conflict of Interest
The authors declare that they have no competing interests.
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