The study will help us in understanding the neural mechanisms by which listeners with a cochlear implant detect speech in noisy environments.

Despite the success of a cochlear implant (CI) for providing or improving hearing ability for people with severe hearing loss, everyday conversations in background noise are still the main clinical complaint. The goal of this study is to understand the neural mechanisms by which listeners with a CI detect speech in noisy environments, and to understand how these mechanisms differ across a variety of CI listeners, in order to determine what variables are most relevant for predicting successful outcome. Therefore the purpose of PET neuroimaging in this study is to find the brain regions that relate to speech in noise effort using PET during auditory stimulation on a single session across a variety of CI users with different device configurations. An age-matched typical hearing control group provides a baseline for comparison. PET neuroimaging will be performed using a radioactive form of water, O-15 (an investigational agent), that will be injected into the body to examine brain blood flow using a PET/CT scanner.

Cochlear Implant subjects (enrollment is planned at N=120) - Inclusion criteria:

1. Between 18 and 99 years of age.
2. Have a cochlear implant activated for more than one year.
3. Eligible for research under the Iowa Cochlear Implant Project VIII.
4. Ability to understand and willingness to sign a written informed consent document.
5. Severe hearing loss after age 16.

Normal Hearing subjects (enrollment is planned at N=30) - Inclusion criteria:

1. Between 18 and 99 years of age.
2. Have age typical hearing.
3. Eligible for research under the Iowa Cochlear Implant Project VIII.
4. Ability to understand and willingness to sign a written informed consent document.

Exclusion criteria (all groups):

1. Medical history includes seizure disorder, head injury, neurologic, metabolic, cardiovascular disease, or previous cerebrovascular event (unless approved by PI).
2. Female self-reporting pregnancy. A urine pregnancy test will be performed prior to injection of the radiopharmaceutical.
3. Currently taking medications which may affect cerebral blood flow (e.g., papaverine, ginkgo biloba, acetazolamide).
4. Uncontrolled intercurrent illness that would limit compliance with study requirements per investigator.