The goal of this research program is to establish a better framework for the use of loudness data in hearing-aid design and ultimately hearing-aid fitting. Several hearing-aid fitting algorithms attempt to restore normal loudness or reduce peaks in loudness, but there is no consensus on appropriate procedures that would enable researchers, engineers or clinicians to verify the extent to which these goals were met. Furthermore, the lack of data on which to base the rules governing the loudness of broadband sounds in listeners with normal hearing (NH) makes it impossible to provide an adequate specification of what restoration of normal loudness in listeners with sensorineural hearing loss (SNHL) would entail. We will explore the use of perceptual weights to establish the contribution of individual frequency bands to the total loudness of broadband sounds. This methodology will allow us to test the basic assumptions underlying current loudness models. The proposed studies are grouped under three specific aims. The first will test the hypothesis that the relation among results obtained with different measurement procedures are independent of the degree of hearing loss. The goal of this aim is to achieve consensus on methods to measure loudness. The second aim will use perceptual weights to test the hypothesis that the contribution of specific frequencies to the total loudness of broadband sounds is influenced by hearing loss. The goal is to explore the effects of level and hearing loss on the specific loudness of broadband sounds, including noise with the long-term spectrum of speech. The final aim will apply methods and insights developed in the course of work on the first two aims to measurements of loudness experienced by new hearing-aid users without and with the amounts of amplification provided by their hearing aids. The studies are designed to assess the extent to which the loudness goals of hearing-aid fitting strategies are met and to explore the effect of acclimatization to hearing aids on loudness perception. The current ANSI standard model of loudness and variations of it guided the design of experiments. The proposed studies are expected to lead to improvements of existing models that will better predict the loudness percepts of individuals with hearing loss, thus potentially leading to better intervention strategies.