Interaural Mismatch in SSD CI Users

Interaural loudness and pitch mismatch in single-sided deaf cochlear implant (SSD-CI) recipients reduces binaural processing cues and contributes to performance outcomes, specifically speech understanding in noise and localization. We aim to improve binaural cues through speech processor program modifications that reduce interaural mismatches.

Effective binaural processing depends on similar loudness growth functions at each ear (Francart et al, 2013, Blamey et al, 2000). The use of interaural level differences (ILDs), perceived as loudness differences, to locate sound is critical given the inability of cochlear implant (CI) recipients to use interaural time differences (ITDs) in binaural processing (Francart et al, 2013, Litovsky et al, 2012). In CI recipients with single-sided deafness (SSD), perceived interaural loudness differences may not be valid indicators of interaural level differences because the CI compresses amplitude (Dorman et al, 2015). Studies suggest better preservation of ILDs may contribute to improved localization and understanding in noise. Since SSD-CI recipients use only one device, an approach to improve their use of ILDs is to match perceived loudness at each ear (Buss et al, 2018). Binaural processing is also affected when signals of equal frequency are not matched in pitch at each ear. In bilateral CI recipients, we found that the greater the pitch mismatch between ears, the poorer the speech understanding in noise. We want to extend this work to SSD-CI recipients. Through CI program modifications, we aim to decrease the pitch and loudness mismatch between the CI ear and the normal hearing ear to improve binaural listening abilities, specifically speech understanding in noise and sound localization.

Testing in noise will be obtained using the R-Space test which simulates listening in a noisy restaurant. The score is a signal-to-noise ratio that reflects 50% speech understanding in noise.

Inclusion Criteria: Participants for the proposed study will be adults with single-sided deafness. Participants will have at least 6 months experience with their cochlear implant or will be newly implanted with the cochlear implant. Inclusion criteria for the experienced CI user group and the newly implant group are as follows: 18 years of age and older Postlingual onset of SSD Pure tone average (PTA) at 500, 1000, and 2000 Hz of less than or equal to 30 dB HL in the contralateral ear, known as the normal hearing ear Implanted with or chosen to be implanted with a Nucleus cochlear implant Full insertion of electrode array Exclusion Criteria: • Not meeting the inclusion criteria