Spectral Dynamics and Speech Understanding by Hearing Impaired People

The purpose of this program of research is to understand the perception of the dynamic spectral properties of speech by hearing-impaired listeners, with the long-term goal of improving speech understanding by these individuals in adverse listening conditions. The proposed research compares the performance of normally-hearing and hearing-impaired listeners on measures of speech understanding in the presence of different types of signal distortion and speech understanding of signals with enhanced spectral dynamics. A computational model based on the amount of potential information available in speech will be used to quantify differences in speech intelligibility due to hearing status and stimulus characteristics.

This is a behavioral study of human auditory perception. Each experiment in this study involves prospective data collection from three types of listeners. The experimental listeners will be people with sensorineural hearing loss and the control listeners will either be subjects with normal hearing or normal-hearing listeners for whom hearing loss will be simulated through the use of a spectrally-shaped broadband noise. The tasks of the subjects in this study involve either listening to synthesized sounds over earphones while seated comfortably in a sound-treated booth, and making responses indicating the subject's auditory perception of these sounds by touching specific areas on a touch-screen terminal; or, listening to recorded, acoustically modified syllables, words, or sentences over earphones and making responses indicating the subject's identification.

Participants with auditory thresholds within the normal limits. age between 18 and 35 individuals with hearing thresholds of 20 dB HL or better at all octave frequencies between 250 Hz and 4000 Hz Acoustic distortion of speech

individuals with bilateral sensorineural hearing losses with thresholds between 25 and 70 dB HL and no losses greater than 70 dB HL at frequencies of 4000 Hz or below age 18 to 65 Acoustic distortion of speech

Participants with auditory thresholds within the normal limits. age between 36 and 65 individuals with hearing thresholds of 20 dB HL or better at all octave frequencies between 250 Hz and 4000 Hz Acoustic distortion of speech

The experimental approach compares speech identification performance among younger, normally-hearing listeners, older normally-hearing listeners and hearing-impaired listeners. Tasks will be carried out in quiet and in the presence of continuous, speech-shaped background noise. The investigators compared the understanding of unprocessed stimuli with 1) time-compressed stimuli, 2) time-compressed stimuli expanded in time via gaps and 3) uncompressed stimuli where portions of the signal were replaced with silence. Experimental metrics were percentage of correct/incorrect speech identification in each listening condition.

average of two blocks per condition obtained over the course of up to three 2-hour visits, spaced an average of one week apart

Inclusion Criteria: individuals with hearing thresholds of 20 dB HL or better at all octave frequencies between 250 Hz and 4000 Hz or, individuals with bilateral sensorineural hearing losses with thresholds between 25 and 70 dB HL and no losses greater than 70 dB HL at frequencies of 4000 Hz or below Exclusion Criteria: a conductive hearing impairment or other otological pathology hearing thresholds greater than 70 dB HL at any frequencies of 4000 Hz or below or pure-tone averages (averaged across 500, 1000, and 2000 Hz) of greater than 65 dB HL bilateral differences greater than 20 dB at any frequency below 4000 Hz an inability to complete the experimental tasks