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  • Title: Localization by postlingually deafened adults fitted with a single cochlear implant.
    Author: Grantham DW, Ricketts TA, Ashmead DH, Labadie RF, Haynes DS.
    Journal: Laryngoscope; 2008 Jan; 118(1):145-51. PubMed ID: 17975505.
    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 degrees to +90 degrees 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 (C). C for three subjects was near chance (50.5 degrees ), whereas C for the remaining three subjects was significantly better than chance (35 degrees -44 degrees ). By comparison, C for a group of normal-hearing listeners was 5.6 degrees . 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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