Does Bilateral Experience Lead to Improved Spatial Unmasking of Speech in Children Who Use Bilateral Cochlear Implants?

HYPOTHESIS In children with bilateral cochlear implants (BiCIs), experience over a 1 to 3-year period can improve speech understanding and spatial unmasking of speech. BACKGROUND One reason for providing children with BiCIs is to improve spatial hearing abilities. Little is known about changes in performance with added bilateral experience, and the relation between sound localization and spatial unmasking of speech. METHODS Twenty children with BiCIs participated. Testing was conducted typically within a year of bilateral activation, and at 1, 2, or 3 follow-up annual intervals. All testing was done while children listened with both devices activated. Target speech was presented from front (co-located); interfering speech was from front, right (asymmetrical), or right and left (symmetrical). Speech reception thresholds (SRTs) were measured in each condition. Spatial release from masking (SRM) was quantified as the difference in SRTs between conditions with interferers at 0 degrees and 90 degrees. For 11 of the children, data are also compared with sound localization measures obtained on the same visit to the laboratory but published elsewhere. RESULTS Change in SRM with bilateral experience varied; some children showed improvement and others did not. Regression analyses identified relationships between SRTs and SRM. Comparison of the SRM with localization data suggests little evidence for correlations between the two spatial tasks. CONCLUSION In children with BiCIs spatial hearing mechanisms involved in SRM and sound localization may be different. Reasons for reduced SRM include asymmetry between the ears, and individual differences in the ability to inhibit interfering information, switch and/or sustain attention.