Delight yourself in the LORD, and he will give you the desires of your heart. Psalm 37:4 The heart of man plans his way, but the LORD establishes his steps. Proverbs 16:9 iv ACKNOWLEDGEMENTS I would like to first thank the members of my dissertation committee for their time and thoughtful comments. I would like to express deepest gratitude to my advisor Dr. Paul Abbas for his full support and expert guidance throughout my research. He also showed me how to be a humble researcher, welcoming all

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... deas from students and young researchers. Also, I express my appreciation to Dr. Carolyn Brown, who is my Iowa mom, for her incredible patience and help throughout Au.D. and Ph.D. programs. I appreciate Dr. Christopher Turner for sharing his wisdom for life as well as research, providing me an opportunity to work in his speech perception laboratory, and encouraging me whenever I felt small in academics. I would like to thank all my teachers and supervisors at the University of Iowa. I thank Drs. Bentler, Finnegan, Wu, Walker, Goodman, and Diane Niebuhr, a clinical professor, for their continuous support. Also, I thank Dr. Holly Teagle and the pediatric cochlear implant (CI) team at the University of North Carolina for teaching me a caring heart for children with a CI. Thanks also go to my fellow at graduate school, Li, Aayesha, Rachel, Bruna, Eli, Viral, Nick, Marcin, and Ben, and the CI research team, especially, Sue, Christine, and Ginny, at the University of Iowa Hospitals and Clinics. Finally but most importantly, I would like to thank God, who gives me the desires of my heart and directs my steps. I thank my parents for their faith and consistent prayers. I thank my brother for sending me many packages, filled with my favorite snacks, from Korea. I appreciate my husband, Jay, who moved from Canada to Iowa and became a huge blessing to me. I thank hugs from my daughter, Ellie. Without her, I couldn't have tasted the extreme joy of being a mom. v ABSTRACT This study investigates the developmental effects on two types of cortical auditory evoked potentials. One is the P1-N1-P2 complex, which occurs within 50 to 250 ms after a stimulus onset. It is also called an onset response and is related to sound detection. Another is the acoustic change complex (ACC), elicited by any acoustic change in ongoing sounds. It is also called a change response and is related to sound discrimination. The aim of the study was to document developmental effects on the P1-N1-P2 and the ACC in normal hearing (NH) listeners and cochlear implant (CI) users in quiet and noise conditions. For NH listeners, ninety-one children aged 3-19 years and eleven young adults participated. A total of fifty-nine CI users participated: forty-eight pre-lingually deafened children aged 3-19 years and young adults, and eleven post-lingually deafened adults. All pre-lingually deafened subjects were implanted with their CI(s) before 3.5 years of age. Speech-like stimuli were presented once in quiet and once in noise conditions to elicit the cortical auditory evoked potentials. Results show that the morphology, latency, and amplitude of both onset and ACC responses showed similar developmental effects. However, the ACC matured later than the onset response in both quiet and noise conditions. With background noise, the ACC was affected by noise more than the onset response, which led to a longer developmental trajectory for the ACC. The findings were similar between NH listeners and CI users, suggesting that a CI facilitates typical development of the two cortical responses. However, the effect of background noise was prominent in the ACC of CI users. This may indicate the perceptual difficulties of discriminating sounds in noise. vi PUBLIC ABSTRACT When a baby is born deaf, a cochlear implant is often recommended as a medical habilitation tool to the parents. A cochlear implant is designed to bypass a damaged cochlea and stimulates auditory nerve directly, from where signals are sent all the way to the auditory cortex where sounds are perceived. We expect that a deaf child can detect and discriminate speech sounds with this device. With continuous auditory experiences, we hope that the auditory cortex of the deaf child can be developed as children with normal hearing do. Can a cochlear implant facilitate the development of the auditory brain? This study attempts to answer this question, exploring developmental effects on evoked potentials measured at the cortical level. Early-implanted, pre-lingually deafened cochlear implant users showed similar developmental patterns of cortical auditory evoked potentials to those of normal hearing listeners. However, the responses, related to sound discrimination, were affected by noise more in cochlear implant users. This may be related to perceptual abilities of cochlear implant users in harder listening conditions. The findings indicate that cortical auditory evoked potentials, related to both detection and discrimination, can be used to document the long developmental trajectory of the central auditory system in both normal hearing listeners and cochlear implant users. This study suggests that these responses can be used as a tool for estimating behavioral performance in cochlear implant users. vii