Volume 103, Issue 1, January 1998
Index of content:
- SPEECH PERCEPTION 
Evaluation of the effect of speech-rate slowing on speech intelligibility in noise using a simulation of cochlear hearing loss103(1998); http://dx.doi.org/10.1121/1.421123View Description Hide Description
The effect of digital processing, which slows the speed of speech (speech-rate) without changing its pitch, has been examined. The processing is intended to make speech communication easier by allowing more time for cognitive processing when the listening situation is difficult, for example, when listening to a foreign language, or when the user has a hearing loss. The speech-rate slowing makes use of a pitch-synchronous partial expansion of the waveform in the time domain. The processing was evaluated using a simulation of hearing loss which has been shown to lead to reduced intelligibility for normally hearing subjects. The simulation included the major consequences of cochlear hearing loss;loudness recruitment, threshold elevation, and reduced frequency selectivity. Two simulations were used: a moderate flat hearing loss with auditory filters broadened by a constant factor of three (B3R2); and the same loss with linear amplification applied prior to the simulation processing Two expansion rates were used for the speech-rate slowing, 1.25 and 1.50. The intelligibility of sentences in speech-shaped noise was measured. For both simulation conditions, the speech-rate slowing did not give any improvement in intelligibility. Rather, in condition the slowing produced statistically significant deleterious effects on intelligibility. The results suggest that artificial speech-rate slowing will not improve the intelligibility of speech in noise for hearing-impaired people who have the type of cochlear damage simulated in this test.
Speech reception thresholds in noise with and without spectral and temporal dips for hearing-impaired and normally hearing people103(1998); http://dx.doi.org/10.1121/1.421128View Description Hide Description
People with cochlear hearing loss often have considerable difficulty in understanding speech in the presence of background sounds. In this paper the relative importance of spectral and temporal dips in the background sounds is quantified by varying the degree to which they contain such dips. Speech reception thresholds in a 65-dB SPLnoise were measured for four groups of subjects: (a) young with normal hearing; (b) elderly with near-normal hearing; (c) young with moderate to severe cochlear hearing loss; and (d) elderly with moderate to severe cochlear hearing loss. The results indicate that both spectral and temporal dips are important. In a background that contained both spectral and temporal dips, groups (c) and (d) performed much more poorly than group (a). The signal-to-background ratio required for 50% intelligibility was about 19 dB higher for group (d) than for group (a). Young hearing-impaired subjects showed a slightly smaller deficit, but still a substantial one. Linear amplification combined with appropriate frequency-response shaping (NAL amplification), as would be provided by a well-fitted “conventional” hearing aid, only partially compensated for these deficits. For example, group (d) still required a speech-to-background ratio that was 15 dB higher than for group (a). Calculations of the articulation index indicated that NAL amplification did not restore audibility of the whole of the speech spectrum when the speech-to-background ratio was low. For unamplified stimuli, the SRTs in background sounds were highly correlated with absolute thresholds, but not with age. For stimuli with NAL amplification, the correlations of SRTs with absolute thresholds were lower, but SRTs in backgrounds with spectral and/or temporal dips were significantly correlated with age. It is proposed that noise with spectral and temporal dips may be especially useful in evaluating possible benefits of multi-channel compression.