Document Detail

Interaural Level Differences and Sound Source Localization for Bilateral Cochlear Implant Patients.
MedLine Citation:
PMID:  25127322     Owner:  NLM     Status:  Publisher    
OBJECTIVES:: The aims of this study were (i) to determine the magnitude of the interaural level differences (ILDs) that remain after cochlear implant (CI) signal processing and (ii) to relate the ILDs to the pattern of errors for sound source localization on the horizontal plane.
DESIGN:: The listeners were 16 bilateral CI patients fitted with MED-EL CIs and 34 normal-hearing listeners. The stimuli were wideband, high-pass, and low-pass noise signals. ILDs were calculated by passing signals, filtered by head-related transfer functions (HRTFs) to a Matlab simulation of MED-EL signal processing.
RESULTS:: For the wideband signal and high-pass signals, maximum ILDs of 15 to 17 dB in the input signal were reduced to 3 to 4 dB after CI signal processing. For the low-pass signal, ILDs were reduced to 1 to 2 dB. For wideband and high-pass signals, the largest ILDs for ±15 degree speaker locations were between 0.4 and 0.7 dB; for the ±30 degree speaker locations between 0.9 and 1.3 dB; for the 45 degree speaker locations between 2.4 and 2.9 dB; for the ±60 degree speaker locations, between 3.2 and 4.1 dB; and for the ±75 degree speaker locations between 2.7 and 3.4 dB. All of the CI patients in all the stimulus conditions showed poorer localization than the normal-hearing listeners. Localization accuracy for the CI patients was best for the wideband and high-pass signals and was poorest for the low-pass signal.
CONCLUSIONS:: Localization accuracy was related to the magnitude of the ILD cues available to the normal-hearing listeners and CI patients. The pattern of localization errors for the CI patients was related to the magnitude of the ILD differences among loudspeaker locations. The error patterns for the wideband and high-pass signals, suggest that, for the conditions of this experiment, patients, on an average, sorted signals on the horizontal plane into four sectors-on each side of the midline, one sector including 0, 15, and possibly 30 degree speaker locations, and a sector from 45 degree speaker locations to 75 degree speaker locations. The resolution within a sector was relatively poor.
Michael F Dorman; Louise Loiselle; Josh Stohl; William A Yost; Anthony Spahr; Chris Brown; Sarah Cook
Publication Detail:
Type:  JOURNAL ARTICLE     Date:  2014-8-14
Journal Detail:
Title:  Ear and hearing     Volume:  -     ISSN:  1538-4667     ISO Abbreviation:  Ear Hear     Publication Date:  2014 Aug 
Date Detail:
Created Date:  2014-8-15     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  8005585     Medline TA:  Ear Hear     Country:  -    
Other Details:
Languages:  ENG     Pagination:  -     Citation Subset:  -    
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