Hybrid Cochlear Implants and Localization
Lammers et al (2014) evaluated 18 subjects who had bilateral low-frequency hearing and were implanted with a hybrid cochlear implant (HCI). The authors note that when traditional cochlear implants (CIs) localize sound they depend on interaural loudness differences (ILDs). The authors queried whether the additional low-frequency acoustic information provided through HCI would provide additional localization cues through interaural timing differences (ITDs).
According to the U.S. Food and Drug Administration (2014), the HCI is “…designed to allow patients to hear in two ways: (1) electronically—similar to approved cochlear implants—for severe to profound hearing loss at mid and high frequencies, and (2) acoustically—similar to hearing aids—for normal-to-moderate hearing loss at low frequencies….the sound processor picks up sound from the patient’s surroundings and separates it into different groups of sounds by frequency. The higher frequency information is sent to the receiver/stimulator and electrode array. Inside the patient’s cochlea, the sound processor also provides amplified low-frequency sound to the patient’s ear through the acoustic component. After implantation, some patients do not have enough low-frequency hearing to use the acoustic component. These patients hear only electrically using the implant for all (lower and higher) sound frequencies….”
Lammers et al reported that the additional acoustic information provided through the HCI did not significantly improve localization ability. They stated that “the fact that the results in the bimodal condition are similar to the results obtained with the conventional CI indicates that sound localization abilities with the shorter (electrode) array are equivalent to the conventional, longer electrode arrays….” They further report that “comparable findings or equivalence between the longer conventional and shorter electrodes has been reported for speech perception tests in quiet and noise….”
For More Information, References, and Recommendations
Lammers MJW, Lenarz T, van Zanten GA, Grolman W, Buechner A. (2014) Sound Localization Abilities of Unilateral Hybrid Cochlear Implant Users with Bilateral Low-Frequency Hearing. Otology & Neurotology 35:1433-1439.