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The Relationship Between Intensity Coding and Binaural Sensitivity in Adults With Cochlear Implants

Todd, Ann E.; Goupell, Matthew J.; Litovsky, Ruth Y.

doi: 10.1097/AUD.0000000000000382
e-Research Articles

Objectives: Many bilateral cochlear implant users show sensitivity to binaural information when stimulation is provided using a pair of synchronized electrodes. However, there is large variability in binaural sensitivity between and within participants across stimulation sites in the cochlea. It was hypothesized that within-participant variability in binaural sensitivity is in part affected by limitations and characteristics of the auditory periphery which may be reflected by monaural hearing performance. The objective of this study was to examine the relationship between monaural and binaural hearing performance within participants with bilateral cochlear implants.

Design: Binaural measures included dichotic signal detection and interaural time difference discrimination thresholds. Diotic signal detection thresholds were also measured. Monaural measures included dynamic range and amplitude modulation detection. In addition, loudness growth was compared between ears. Measures were made at three stimulation sites per listener.

Results: Greater binaural sensitivity was found with larger dynamic ranges. Poorer interaural time difference discrimination was found with larger difference between comfortable levels of the two ears. In addition, poorer diotic signal detection thresholds were found with larger differences between the dynamic ranges of the two ears. No relationship was found between amplitude modulation detection thresholds or symmetry of loudness growth and the binaural measures.

Conclusions: The results suggest that some of the variability in binaural hearing performance within listeners across stimulation sites can be explained by factors nonspecific to binaural processing. The results are consistent with the idea that dynamic range and comfortable levels relate to peripheral neural survival and the width of the excitation pattern which could affect the fidelity with which central binaural nuclei process bilateral inputs.

1Waisman Center, University of Wisconsin-Madison, Madison, Wisconsin, USA; and 2Department of Hearing and Speech Sciences, University of Maryland, College Park, Maryland, USA.

This study was supported by NIH Grant R01DC003083 (to R.Y.L.), R01DC014948 (to M.J.G.), and F31DC013238 (to A.E.T.). Support was also provided by NIH Grant P30HD03352 (to the Waisman Center).

Portions of this article represent the PhD dissertation work of A.E.T., and were presented at the 38th Annual Mid-Winter Meeting of the Association for Research in Otolaryngology on February, 22, 2015 in Baltimore, MD.

The authors have no conflicts of interest to disclose.

Received March 30, 2016; accepted August 30, 2016.

Address for correspondence: Ann E. Todd, Department of Otolaryngology, New York University, 462 1st Ave, NBV 5E5, New York, NY 10016, USA. E-mail: anntodd3@gmail.com

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