The proposed work will evaluate the feasibility and efficacy of using laboratory and wearable versions of a digital signal-processing (DSP) development system in research and clinical studies of the reliability and validity of hearing aid fitting procedures. A multiple-baseline, "time-lagged control," design will used in conjunction with a new preference-based fitting procedure to demonstrate the nature of the relationships between preference behavior of hearing-impaired individuals in laboratory test situations and preferences under real-world conditions. Reliability of frequency response preferences in the laboratory and in the real world, and the effects of real-world experience with hearing aids on judgments of aided performance in different listening situations and environments simulated in the laboratory, will be investigated. The proposed work is expected to establish basic conditions under which frequency response characteristics can be fitted reliably and validly to individual hearing-impaired listeners. Ultimately, this research may lead to the development and evaluation of improved algorithms for resolving the communicative difficulties faced by hearing-impaired persons in a variety of listening situations.