Authors: Darby Durbin¹, Victoria Sweeney¹, Z. Ellen Peng¹
¹Boys Town National Research Hospital
Background: Bilateral cochlear implants (CIs) provide some access to spatial hearing for individuals with severe to profound hearing loss. Although poorer than normal-hearing (NH) peers, many bilateral CI users demonstrate spatial acuity, the ability to discriminate between two adjacent sound sources. However, in daily listening situations such as indoor spaces, reverberation distorts important binaural cues causing reduced spatial acuity for NH listeners. There is a need to quantify spatial acuity under realistic reverberation for bilateral CI listeners in real-world listening environments.
Method: Spatial acuity was measured with minimum audible angle (MAA) using a three-interval, two-alternative forced choice adaptive procedure. MAA just-noticeable-difference (JND) thresholds were defined for each subject as the smallest angle at 70.7% correct around 0° azimuth. MAA thresholds were compared between 16 bilateral CI participants aged 9-23 years old and 39 NH participants aged 8-13 years old when tested using two tokens (i.e., speech-shaped noise and disyllabic word) and under three different levels of reverberation (i.e., anechoic, low-reverberation, and high-reverberation).
Results: When tested using the speech-shaped noise token, bilateral CI users showed a significant elevation in MAA thresholds from anechoic by 18 ° in high reverberation, but a non-significant elevation of 6° in low reverberation. With the disyllabic word token, MAA thresholds for bilateral CI users were non-significantly elevated from anechoic by 11° in high reverberation and by 2° in low reverberation.
Conclusion: This investigation demonstrated that bilateral CIs can provide users with access to discriminate frontal spatial locations even under varying levels of realistic reverberation. Further, bilateral CI users experienced poorer spatial acuity with high but not necessarily low reverberation, showing a similar behavioral trend as NH peers.
