Word Recognition for Temporally and Spectrally Distorted Materials:The Effects of Age and Hearing Loss

Objectives: The purpose of Experiment 1 was to measure word recognition in younger adults with normal hearing when speech or babble was temporally or spectrally distorted. In Experiment 2, older listeners with near-normal hearing and with hearing loss (for pure tones) were tested to evaluate their susceptibility to changes in speech level and distortion types. The results across groups and listening conditions were compared to assess the extent to which the effects of the distortions on word recognition resembled the effects of age-related differences in auditory processing or pure-tone hearing loss. Design: In Experiment 1, word recognition was measured in 16 younger adults with normal hearing using Northwestern University Auditory Test No. 6 words in quiet and the Words-in-Noise test distorted by temporal jittering, spectral smearing, or combined jittering and smearing. Another 16 younger adults were evaluated in four conditions using the Words-in-Noise test in combinations of unaltered or jittered speech and unaltered or jittered babble. In Experiment 2, word recognition in quiet and in babble was measured in 72 older adults with near-normal hearing and 72 older adults with hearing loss in four conditions: unaltered, jittered, smeared, and combined jittering and smearing. Results: For the listeners in Experiment 1, word recognition was poorer in the distorted conditions compared with the unaltered condition. The signal to noise ratio at 50% correct word recognition was 4.6 dB for the unaltered condition, 6.3 dB for the jittered, 6.8 dB for the smeared, 6.9 dB for the double-jitter, and 8.2 dB for the combined jitter-smear conditions. Jittering both the babble and speech signals did not significantly reduce performance compared with jittering only the speech. In Experiment 2, the older listeners with near-normal hearing and hearing loss performed best in the unaltered condition, followed by the jitter and smear conditions, with the poorest performance in the combined jitter-smear condition in both quiet and noise. Overall, listeners with near-normal hearing performed better than listeners with hearing loss by ∼30% in quiet and ∼6 dB in noise. In the quiet distorted conditions, when the level of the speech was increased, performance improved for the hearing loss group, but decreased for the older group with near-normal hearing. Recognition performance of younger listeners in the jitter-smear condition and the performance of older listeners with near-normal hearing in the unaltered conditions were similar. Likewise, the performance of older listeners with near-normal hearing in the jitter-smear condition and the performance of older listeners with hearing loss in the unaltered conditions were similar. Conclusions: The present experiments advance our understanding regarding how spectral or temporal distortions of the fine structure of speech affect word recognition in older listeners with and without clinically significant hearing loss. The Speech Intelligibility Index was able to predict group differences, but not the effects of distortion. Individual differences in performance were similar across all distortion conditions with both age and hearing loss being implicated. The speech materials needed to be both spectrally and temporally distorted to mimic the effects of age-related differences in auditory processing and hearing loss

Speech understanding and listening effort in noise with a new speech processing algorithm

This study examined the effect of a new speech processing strategy (SpeechZone2) in a commercially available hearing aid on speech understanding in noise and self-reported listening effort. Seven adult, experienced hearing aid users (2 males, 5 females; mean age = 64.6 years) with mild to severe, sloping sensorineural hearing loss participated in this study. Binaural Unitron Flex receiver in the ear style hearing aids with closed domes were used to provide the manufacturer prescribed amplification for each participant. The hearing aids were programmed with two separate memories: 1) omnidirectional microphone without SpeecZone2 processing, and 2) adaptive directionality with SpeechZone2 processing. The participants were seated in the center of a five loudspeaker fixed array. HINT scores (dB SNR required for 50% speech understanding) with the speech source at 00, 900, 1800, and 2700 azimuths were measured for each program while uncorrelated speech babble noise was presented simultaneously from four speakers. The participants were also asked to fill out a short questionnaire on listening effort after each condition. Results showed that the new speech processing algorithm (adaptive directionality with SpeechZone2) did not improve speech understanding in noise compared to the omnidirectional microphone condition (F(1,6)= 1.723; p = 0.237). Pairwise comparison with Bonferroni corrections (α=0.0125) indicated that there was a significant improvement only when speech was presented from 270 degree azimuth (p=0.002). The ANOVA also revealed a significant effect of the speech source location (F(3,18)= 5.62; p=0.02). Regardless of the directionality and speech processing, the participants performed better when speech was presented from the sides (900 and 2700). A Wilcoxon signed-rank nonparametric test showed that there was no significant difference in the self-reported scores in the listening effort questionnaire (Z = 0.637, p = 0.39). There was a large intersubject variability noticed in this small sample size