Understanding Frequency Encoding and Perception in Adult Users of Cochlear Implants
Faulkner, Kathleen Ferrigan
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An increasingly common approach to treating severe to profound hearing loss in children and adults is cochlear implantation, with over 219,000 users worldwide. While most cochlear implant (CI) users achieve high levels of speech understanding in quiet, many continue to struggle with speech in the presence of background noise and music appreciation. One working hypothesis is that these deficits are related to impaired spectral resolution with CIs. Both device-related and patient-related factors are thought to contribute to impaired spectral resolution. This series of experiments were conducted to identify ways to improve spectral resolution in individuals using two approaches. First, a device-centered approach was used with a focused stimulus configuration to determine if it was possible to identify poorly-functioning CI channels with the hopes of improving how CIs are mapped clinically, using a behavioral (experiment 1) and an objective measure (experiment 2). Given that spectral resolution is likely not entirely related to device factors, and not all aspects of the device are modifiable or controllable, we also set out to determine if we could improve the implant user's ability to make use of the information they receive with their implant through auditory training (experiment 3). The results of the first two experiments demonstrated that problem channels can be identified using behavioral (single-channel thresholds and tuning curves) and objective measures (EABR). Using a single-subject design, we also showed that it is possible to alter perception of frequency through auditory training. All trained subjects improved on tests of speech in noise, but improvements did not generalize to tests of speech in quiet, music perception, or quality of life. The pattern of learning suggests that the improvements cannot be entirely explained by improved spectral resolution, and motivates future directions aimed at understanding what mechanism of action in the training paradigm contributed to improved speech reception in noise.
- Speech