Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)


Speech and Hearing Science

Research Advisor

Patrick N. Plyler, Ph.D.


Ashley Harkrider, Ph.D. Patti Johnstone, Ph.D. Greg Petty, Ph.D.


Age, Directionality, Localization, Occlusion


Localization acuity of a given listener is dependent upon the ability discriminate between interaural time and level disparities. Interaural time differences are encoded by low frequency information whereas interaural level differences are encoded by high frequency information. Much research has examined effects of hearing aid microphone technologies and occlusion separately and prior studies have not evaluated age as a factor in localization acuity. Open-fit hearing instruments provide new earmold technologies and varying microphone capabilities; however, these instruments have yet to be evaluated with regard to horizontal localization acuity.

Thus, the purpose of this study is to examine the effects of microphone configuration, type of dome in open-fit hearing instruments, and age on the horizontal localization ability of a given listener. Thirty adults participated in this study and were grouped based upon hearing sensitivity and age (young normal hearing, >50 years normal hearing, >50 hearing impaired). Each normal hearing participant completed one localization experiment (unaided/unamplified) where they listened to the stimulus "Baseball" and selected the point of origin. Hearing impaired listeners were fit with the same two receiver-in-the-ear hearing aids and same dome types, thus controlling for microphone technologies, type of dome, and fitting between trials. Hearing impaired listeners completed a total of 7 localization experiments (unaided/unamplified; open dome: omnidirectional, adaptive directional, fixed directional; micromold: omnidirectional, adaptive directional, fixed directional).

Overall, results of this study indicate that age significantly affects horizontal localization ability as younger adult listeners with normal hearing made significantly fewer localization errors than older adult listeners with normal hearing. Also, results revealed a significant difference in performance between dome type; however, upon further examination was not significant. Therefore, results examining type of dome should be viewed with caution. Results examining microphone configuration and microphone configuration by dome type were not significant. Moreover, results evaluating performance relative to unaided (unamplified) were not significant. Taken together, these results suggest open-fit hearing instruments, regardless of microphone or dome type, do not degrade horizontal localization acuity within a given listener relative to their 'older aged' normal hearing counterparts in quiet environments.