SIMULATION OF THE EFFECT OF THRESHOLD ELEVATION AND LOUDNESS RECRUITMENT COMBINED WITH REDUCED FREQUENCY-SELECTIVITY ON THE INTELLIGIBILITYOF SPEECH IN NOISE

The effect of loudness recruitment and threshold elevation together wi th reduced frequency selectivity have been simulated to examine the co mbined effect of the two major consequences of cochlear hearing loss o n the intelligibility of speech in speech-shaped noise. In experiment 1, four conditions were simulated: a moderate flat loss with auditory filters broadened by a factor of three (B3R2); a moderate-to-severe sl oping loss with auditory filters broadened by a constant factor of thr ee (B3RX); and these conditions with linear amplification applied prio r to the simulation processing (B3R2+, B3RX+). For conditions B3R2 and B3RX, performance was markedly worse than for a control condition (no rmal hearing, condition R1) tested in a previous study. For conditions B3R2+ and B3RX+, linear amplification improved performance considerab ly. However, performance remained below that for condition R1 by betwe en 5% and 19%. In experiment 2 the broadening of the auditory filters was made more realistic by making it a function of the absolute thresh old at the center frequency of the auditory filter. Three different he aring losses were simulated: a moderate-to-severe sloping loss with va riable broadening of the auditory filters (BXRX); the same moderate-to -severe sloping loss with linear amplification (BXRX+); and the same b roadening of the auditory filters but without the simulation of loudne ss recruitment and threshold elevation (BX). For condition BXRX, perfo rmance was markedly worse than in condition R1, while performance in c ondition BX was somewhat worse than for condition R1. For condition BX RX+, linear amplification according to the NAL procedure improved perf ormance to a targe extent but it remained worse than for condition R1. The results are consistent with previous evidence indicating that onl y part of the decrease of performance produced by actual cochlear hear ing loss can be compensated by conventional linear hearing aids. (C) 1 997 Acoustical Society of America.