Localization by postlingually deafened adults fitted with a single cochlear implant.
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.


METHODS
: 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.
Grantham
D Wesley
DW
Department of Hearing & Speech Sciences, Vanderbilt Bill Wilkerson Center for Otolaryngology and Communication Sciences, Vanderbilt University Medical Center, 1215 21st Avenue South, Nashville, TN 37232, USA. d.wesley.grantham@vanderbilt.edu
Ricketts
Todd A
TA
Ashmead
Daniel H
DH
Labadie
Robert F
RF
Haynes
David S
DS
D000161:Acoustic Stimulation / Q000379:methods; D000328:Adult; D000368:Aged; D003054:Cochlear Implants; D003463:Cues; D003638:Deafness / Q000601:surgery*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009622:Noise; D013017:Sound Localization / Q000502:physiology*; D013067:Speech Perception / Q000502:physiology