Localization by Postlingually Deafened Adults Fitted With a Single Cochlear Implant

Authors

  • D Wesley Grantham PhD,

    Corresponding author
    1. From the Department of Hearing & Speech Sciences, Vanderbilt Bill Wilkerson Center for Otolaryngology and Communication Sciences, Vanderbilt University Medical Center, Nashville, Tennessee.
    • D. Wesley Grantham, Vanderbilt Bill Wilkerson Center for Otolaryngology and Communication Sciences, Vanderbilt University Medical Center, 1215 21st Avenue South, Room 8310, Nashville, Tennessee 37232-8242, U.S.A.
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  • Todd A. Ricketts PhD,

    1. From the Department of Hearing & Speech Sciences, Vanderbilt Bill Wilkerson Center for Otolaryngology and Communication Sciences, Vanderbilt University Medical Center, Nashville, Tennessee.
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  • Daniel H. Ashmead PhD,

    1. From the Department of Hearing & Speech Sciences, Vanderbilt Bill Wilkerson Center for Otolaryngology and Communication Sciences, Vanderbilt University Medical Center, Nashville, Tennessee.
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  • Robert F. Labadie MD, PhD,

    1. Department of Otolaryngology, Vanderbilt Bill Wilkerson Center for Otolaryngology and Communication Sciences, Vanderbilt University Medical Center, Nashville, Tennessee.
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  • David S. Haynes MD

    1. Department of Otolaryngology, Vanderbilt Bill Wilkerson Center for Otolaryngology and Communication Sciences, Vanderbilt University Medical Center, Nashville, Tennessee.
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  • Supported by MED-EL Corporation, Durham, North Carolina, U.S.A.

Abstract

Objective: The main purpose of the study was to assess the ability of adults with unilateral cochlear implants to localize noise and speech signals in the horizontal plane.

Design: Six unilaterally implanted adults, all postlingually deafened and all fitted with MED-EL COMBI 40+ devices, were tested with a modified source identification task. Subjects were tested individually in an anechoic chamber, which contained an array of 43 numbered loudspeakers extending from –90° to +90° azimuth. On each trial, a 200 millisecond signal (either a noise burst or a speech sample) was presented from one of nine active loudspeakers, and the subject had to identify which source (from the 43 loudspeakers in the array) produced the signal.

Results: The relationship between source azimuth and response azimuth was characterized in terms of the adjusted constant error (Ĉ). Ĉ for three subjects was near chance (50.5°), whereas Ĉ for the remaining three subjects was significantly better than chance (35°–44°). By comparison, Ĉ for a group of normal-hearing listeners was 5.6°. For two of the three subjects who performed better than chance, monaural cues were determined to be the basis for their localization performance.

Conclusions: Some unilaterally implanted subjects can localize sounds at a better than chance level, apparently because they can learn to make use of subtle monaural cues based on frequency-dependent head-shadow effects. However, their performance is significantly poorer than that reported in previous studies of bilaterally implanted subjects, who are able to take advantage of binaural cues.

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