Investigating long-term effects of cochlear implantation in single-sided deafness

Objectives: To evaluate methods for measuring long-term benefits of cochlear implantation in a patient with single-sided deafness (SSD) with respect to spatial hearing and to document improved quality of life because of reduced tinnitus.

Patient: A single adult male with profound right-sided senso-rineural hearing loss and normal hearing in the left ear who underwent right-sided cochlear implantation.

Methods: The subject was evaluated at 6, 9, 12, and 18 months after implantation on speech intelligibility with specific target-masker configurations, sound localization accuracy, audiologic performance, and tinnitus handicap. Testing conditions involved the acoustic (NH) ear only, the cochlear implant (CI) ear (acoustic ear plugged), and the bilateral condition (CI+NH). Measures of spatial hearing included speech intelligibility improvement because of spatial release from masking (SRM) and sound localization. In addition, traditional measures known as "head shadow," "binaural squelch," and "binaural summation" were evaluated.

Results: The best indicator for improved speech intelligibility was SRM, in which both ears are activated, but the relative locations of target and masker(s) are manipulated. Measures that compare performance with a single ear to performance using bilateral auditory input indicated evidence of the ability to integrate inputs across the ears, possibly reflecting early binaural processing, with 12 months of bilateral input. Sound localization accuracy improved with addition of the implant, and a large improvement with respect to tinnitus handicap was observed.

Conclusion: Cochlear implantation resulted in improved sound localization accuracy when compared with performance using only the NH ear, and reduced tinnitus handicap was observed with use of the implant. The use of SRM addresses some of the current limitations of traditional measures of spatial and binaural hearing, as spatial cues related to target and maskers are manipulated, rather than the ear(s) tested. Sound testing methods and calculations described here are therefore recommended for assessing performance of a larger sample size of individuals with SSD who receive a CI.