Supported by MED-EL Corporation, Durham, North Carolina, U.S.A.
Localization by Postlingually Deafened Adults Fitted With a Single Cochlear Implant†
Article first published online: 2 JAN 2009
Copyright © 2008 The Triological Society
Volume 118, Issue 1, pages 145–151, January 2008
How to Cite
Grantham, D. W., Ricketts, T. A., Ashmead, D. H., Labadie, R. F. and Haynes, D. S. (2008), Localization by Postlingually Deafened Adults Fitted With a Single Cochlear Implant. The Laryngoscope, 118: 145–151. doi: 10.1097/MLG.0b013e31815661f9
- Issue published online: 2 JAN 2009
- Article first published online: 2 JAN 2009
- Manuscript Accepted: 23 JUL 2007
- Sound localization;
- cochlear implants;
- monaural localization
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.