INTENSITY DLS AND MASKING IN NORMAL AND IMPAIRED HEARING

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Our long term objective is to reach an understanding of the auditory system that will allow quantitative modeling of the perception of tones, noise, and speech in both normal and impaired hearing. Such models are important for understanding normal auditory processes and provide a basis for improving diagnosis and rehabilitation of hearing-impaired listeners. The proposed project aims to obtain psychoacoustic data that will allow further tests of the concept that excitation patterns and multi-band decision rules may provide a general framework for quantitative modeling of normal and impaired hearing. Based on 21,2AFC experiments, in normal, impaired, and masked-normal listeners, the proposed project will establish a firm basis for refining our excitation-pattern model of intensity discrimination and testing a number of hypotheses related to the decision process in this and other models. Our specific aims are: (1) to test the hypothesis that excitation-level Information decreases over time due to adaptation processes in the auditory system, intensity DLs for multiple tone bursts will be measured as functions of the number of bursts and the interburst interval. In other experiments, intensity DLs for brief tones will be measured in the presence of a preceding, adapting tone of various durations; (2) to provide a direct test of the hypothesis that Comodulation Masking Release, CMR, results from "listening in the valleys" and can be explained by an energy-detector model with a stimulus-driven, time-varying weighting of the signal channel, Conditional-On-a-Single-Stimulus (COSS) detection-probability functions will be measured for stimuli presented in multi-band maskers with coherent envelopes (which produce CMR) and with incoherent envelopes (which do not produce CMR); (3) to test the hypothesis that stimulus-driven, time-varying weights affect temporal integration for detection of a tone masked by noise, thresholds for tones presented in gated and continuous maskers with and without cue tones will be measured as a function of signal duration; (4) to assess how stimulus parameters govern the channel weights, thresholds for brief tones presented in gated maskers of various bandwidths will be measured as a function of a cue tone's level and duration; (5) to test the hypothesis that stimulus-driven, time-varying weights cause across-frequency integration to depend on signal duration and listening condition, thresholds for multi-tone complexes of various bandwidths will be measured as functions of stimulus duration and listening condition (gated versus continuous masker, signal bandwidth fixed or randomized across trials, and cue present or absent); (6) to test the hypothesis that widened attention bands obtained in gated maskers reflect the operation of stimulus-driven, time-varying weights, measurements on how attention bandwidth is affected by presentation of a cue prior to each signal interval will be obtained as functions of the masker's off-time and the masker-signal onset separation. These data will add significantly to our understanding of normal and impaired hearing and will be important for the development and testing of models of the auditory system.