Estimation of client-assessed hearing aid performance based upon unaided variables.

The purpose of this study was to investigate the possibility of estimating client-assessed hearing aid performance before hearing aids are purchased. Aided performance was represented by the Profile of Hearing Aid Performance (PHAP, Cox & Gilmore, 1990). Multiple regression was applied to 16 unaided predictor variables and to 8 response variables. The response variables were the scores from the seven PHAP subscales plus the overall PHAP score, which were obtained from 46 participants. Audiologic, demographic, and psychological information was included among the 16 predictor variables. The average widths of 95% prediction intervals showed that, with the exception of the Aversiveness of Sounds and Ease of Communication subscales, PHAP subscale scores were predicted within 15% on average. Eighty percent or more of the individual participants' PHAP scores were predicted within 15% for all but the Aversiveness of Sounds subscale. The predictor variables appearing in regression equations for the greatest number of PHAP subscales include age, Communication Strategies and Personal Adjustment scores from the Communication Profile for the Hearing Impaired (Demorest & Erdman, 1986), Revised Speech Perception in Noise (Bilger, Neutzel, Rabinowitz, & Rzeczkowski, 1984; Kalikow, Stevens, & Elliott, 1977) test scores, comfortable loudness levels, and the difference between National Acoustic Laboratories' target gain (Byrne & Dillon, 1986) and actual insertion gain. Further testing of the models on additional participants would be needed to determine their clinical applicability. In addition to being potentially useful for predicting client-assessed aided performance, the equations obtained in this study identify relationships between the aided and unaided variables that can be applied in the counseling of new hearing aid users.

Discriminability of the quality of amplitude-compressed speech.

In an earlier experiment on intelligibility of amplitude-compressed speech, subjects could not hear a difference between noncompressed speech and speech under some conditions of compression. Therefore, compression conditions were determined in which the quality of the two types of speech could be distinguished. When speech average level was 10 dB above a masking noise, compression ratio (CR) was equal to 2.5, and the attack time (Ta) was 3 ms, the release time (Tr) had to be shorter than 120 ms to achieve discrimination by trained normal-hearing subjects. With longer attack times and/or higher compression ratios, the critical value of release times increased. Thus, the range in which the discrimination was observed also increased (for CR = 5 and Ta = 10 ms, the critical Tr was 360 ms). The discrimination of our hearing-impaired subjects was much worse than that of the normal-hearing subjects. For example, speech processed with CR = 10, Ta = 1 ms, and Tr = 10 ms could be distinguished from the noncompressed by only 50% of the impaired subjects.

Performance of hearing-impaired listeners under various types of amplitude compression.

Speech perception by subjects with sensorineural hearing impairment was studied using various types of short-term (syllabic) amplitude compression. Average speech level was approximately constant. In quiet, a single-channel wideband compression (WBC) with compression ratio equal to 10, attack time 10 ms and release time 90 ms produced significantly higher scores than a three-channel multiband compression (MBC) or no compression when a nonsense syllable test (City University of New York) was used. The scores under MBC, WBC, or no compression were not significantly different when the modified rhyme test (MRT) was used. But when overshoots caused by compression were clipped, the MRT scores improved significantly. The influence of MBC on reverberant speech and of WBC on noisy speech were tested with the MRT. Reverberation reduced the scores, and this reduction was the same with compression as without. Noise added to speech before compression also reduced the scores, but the reduction was larger with compression than without. When noise was added after compression, an improvement was observed when WBC had a compression ratio of about 5, attack time 1 ms, and release time 30 ms. Other compression modes (e.g., with high-frequency pre-emphasis) did not show an improvement. The results indicate that WBC with a compression ratio around 5, attack time shorter than 3 ms, and release time between 30 and 90 ms can be beneficial if signal-to-noise ratio is large, or, if in a noisy or reverberant environment, the effects of noise or reverberation are eliminated by using listening systems.

Temporal summation of constant and gliding tones at masked auditory threshold.

Masked thresholds for constant and gliding tones were determined by the method of adjustment for durations between 0.5 and 5000 ms in three overlapping frequency regions between 0.25 and 3.3 kHz. The masker was a continuous white noise at 70-dB SPL. Listening was monaural; subjects had normal hearing. Below 10 ms the thresholds for upward glides were lower and those for downward glides higher than the thresholds for constant tones. In the 10--300 ms duration range, which encompasses formant transitions of speech, the highest thresholds are for downward glides and the lowest ones for constant tones. These differences could result from different time courses of neural decay and inhibition for constant tones, upward and downward glides. The differences between upward and downward glides indicate that the phase spectra influence sound detectability. The thresholds for constant tones reach minimum around 1 s. The thresholds for glides continue to decrease at least up to 5 s. The "critical" duration for constant tone integration can result from the overriding of integration effects by adaptation effects, the latter ones being eliminated by changing frequency. The curves for constant-tone threshold between 10- and 1000-ms duration were fitted by a product of exponential and hyperbolic functions.

A comparison of hearing aids with amplitude compression.

Intelligibility scores with a modified rhyme test were obtained for normally hearing subjects and subjects with sensorineural hearing impairment using several commercial hearing aids. These hearing aids differed mainly in values of time constants of compression and of harmonic distortion during overshoots. In general, better performance was obtained for the shorter time constants of compression, but performance seemed also to be affected by the occurrence of higher levels of harmonic distortion and of peak-clipping during overshoots.