Research Studies Involving Cochlear Implants

The Iowa Cochlear Implant Project at The University of Iowa under the direction of Bruce Gantz, MD, professor and head of otolaryngology, is supported by a $11 million grant from the National Institute on Deafness and Other Communication Disorders (NIDCD). This is the fifth NIDCD grant that the Iowa Cochlear Implant Program has received from the National Institutes of Health.

Interrelated research projects that address the goals of this project include:

  • Acoustic plus Electric
  • Speech and Language Outcomes
  • Speech and Language Processing
  • Electrophysiology

Acoustic plus Electric Directed by Christopher Turner, PhD

Preservation of residual acoustic hearing during cochlear implantation has become an important improvement in the performance of cochlear implants. Not only does it improve the performance of implants (particularly for noisy, real-world listening conditions) but also allows the treatment of patients with severe high-frequency heaing loss, who have substantial low-frequency hearing. This project proposes to continue this work on combining acoustic plus electric (A+E) hearing. In addition to the overall goal of improving patient care for hearing loss, several unique research opportunities arise from this work. First, because the short-electrode Hybrid implant assigns low- and mid-frequency speech bands to basal locations in the cochlea we have a unique opportunity to study the effects of remapping, neural plasticity, and adaptation to highly-distorted place-frequency maps in the cochlea. The second opportunity arises because of the new population of patients that will be implanted with these A+E devices. Never before have patients with such high levels of pre-operative residual hearing been implanted in such a large-scale project. We are at the same time seeing levels of performance for the transmission of speech through the short electrode that are surprising in light of the previous literature. This will allow us to re-examine some of the commonly held beliefs about the limitations of electric stimulation due to channel interaction.

Speech and Language Outcomes Directed by Bruce Tomblin, PhD, and Camille Dunn, PhD

Research on the communication and academic achievement of children receiving cochlear implants (CI) shows that these children become functional members of the hearing community alongside other children with less severe hearing loss who wear hearing aids (HAs). The extent to which children with CIs have similar functional capabilities will be addressed in this research program. We will obtain data on non-speech auditory perception, speech perception, music perception, speech, language, reading skills and service provision for a group of children fitted with unilateral, bimodal or bilateral CIs. These data will be compared qualitatively and quantitatively with mild to severe hard of hearing (HH) age mates. This research will lead to evidence-based clinical guidelines in determining candidacy criteria for cochlear implants or hearing aids.

Secondly, CIs that preserve residual acoustic hearing (hybrid devices) have been shown to provide hearing benefits to adults with some residual hearing but, these devices have not yet been used with children. In this study, children who are 5 to 15 years of age with moderate to severe hearing loss will receive a hybrid cochlear implant. Speech perception, speech production, language, music perception outcomes will be compared to bimodal and HH children. This aim explores an alternative for children who have some residual hearing, but are not benefitting from conventional hearing aids, to simultaneously take advantage of electric stimulation and their natural acoustic hearing.

Finally, this project will evaluate the feasibility implanting children with profound deafness with a short electrode in one ear and a standard-length electrode in the other ear. The purpose is an attempt to preserve regions of the cochlear partition future medical interventions in the ear with the short electrode. A within-subject design will evaluate equivalency between the ear with the short electrode array and the ear with the standard-length array on speech perception and electrophysiological measures.

Speech and Language Processing Directed by Karen Kirk, PhD, and Bob McMurray, PhD

The majority of studies examining speech perception in cochlear implant recipients have emphasized performance outcomes, that is, how well linguistic messages are understood. These studies have demonstrated large individual differences in speech and language outcomes following cochlear implantation. The reasons for this variability are not well understood, in part because we know little about how cochlear implant recipients use information in the speech signal to arrive at the intended message. The primary goal of the proposed work is to examine the central perceptual and cognitive processes used during spoken language comprehension that may contribute to variation in performance. Using empirical techniques from basic science, the proposed work will examine mechanisms of lexical processing and perceptual learning in a variety of cochlear implant users, including a group of cochlear implant participants implanted with novel hearing-preservation electrodes. The proposed research further will examine whether differences in these perceptual processing mechanisms are associated with individual variations in cochlear implant outcomes. Across the sample, this work will examine how the nature of the auditory input (electric vs. acoustic plus electric) influences lexical access, perceptual normalization, and perceptual learning in adults and children with cochlear implants. In cooperation with Projects 1 (A+E), 2 (Speech/Language Outcomes), 4 (Electrophysiology) and 5 (Music), the relationship between performance on these process-based measures and performance on other auditory and cognitive tasks will be analyzed. The results should simultaneously extend basic psycholinguistic theory and inform the development of cochlear implant processing strategies, candidate selection and novel therapeutic interventions for cochlear implant users.

Electrophysiology Directed by Paul Abbas, PhD, and Carolyn Brown, PhD

An overall goal of this center grant is to evaluate the possible advantages that cochlear implants designed to preserve acoustic hearing (Hybrid cochlear implants) might have for potential implant recipients. The experiments included in this project use electrophysiological recording techniques, both peripheral (compound action potential) and central (cortical change response) to address two important issues. First, how is complex spectral information, presented through both acoustic and electric modes, processed within the auditory system? Secondly, how is that processing changed with implant experience and training on specific tasks. These studies, which primarily address physiological measures and mechanisms, have been designed to integrate closely with the four other projects that focus primarily on the use of perceptual measures of performance in the same subject groups. The peripheral physiological measures will provide a way to characterize the limitations in the information transfer imposed by the speech processor and the auditory nerve. The cortical potentials, evoked in response to complex spectral stimuli (music, speech, and noise stimuli with relatively complex spectral profiles), will allow us to characterize at least one aspect of signal processing in the central auditory pathways. Finally, these physiological measures will be compared with performance data, collected in conjunction with other projects that make up this center grant. A statistical path analysis model will allow us to evaluate the relative contributions of different levels of physiological processing to perception. We will accomplish this in studies examining different subject groups - comparing normal hearing, Hybrid implant users, and standard implant users to address questions of how acoustic and electric stimulation is integrated by the nervous system. We also propose a series of experiments making within-subject comparisons to evaluate the effects of specific training regimens, and in particular, the predictive value of evoked potential measures in assessing training effectiveness in an individual.