Effect of audibility on better-ear glimpsing as a function of frequency in normal-hearing and hearing-impaired listeners.

Better-ear glimpsing (BEG) is an auditory phenomenon that helps understanding speech in noise by utilizing interaural level differences (ILDs). The benefit provided by BEG is limited in hearing-impaired (HI) listeners by reduced audibility at high frequencies. Rana and Buchholz [(2016). J. Acoust. Soc. Am. 140(2), 1192-1205] have shown that artificially enhancing ILDs at low and mid frequencies can help HI listeners understanding speech in noise, but the achieved benefit is smaller than in normal-hearing (NH) listeners. To understand how far this difference is explained by differences in audibility, audibility was carefully controlled here in ten NH and ten HI listeners and speech reception thresholds (SRTs) in noise were measured in a spatially separated and co-located condition as a function of frequency and sensation level. Maskers were realized by noise-vocoded speech and signals were spatialized using artificially generated broadband ILDs. The spatial benefit provided by BEG and SRTs improved consistently with increasing sensation level, but was limited in the HI listeners by loudness discomfort. Further, the HI listeners performed similar to NH listeners when differences in audibility were compensated. The results help to understand the hearing aid gain that is required to maximize the spatial benefit provided by ILDs as a function of frequency.

Effect of improving audibility on better-ear glimpsing using non-linear amplification.

Better-ear glimpsing (BEG) utilizes interaural level differences (ILDs) to improve speech intelligibility in noise. This spatial benefit is reduced in most hearing-impaired (HI) listeners due to their increased hearing loss at high frequencies. Even though this benefit can be improved by providing increased amplification, the improvement is limited by loudness discomfort. An alternative solution therefore extends ILDs to low frequencies, which has been shown to provide a substantial benefit from BEG. In contrast to previous studies, which only applied linear stimulus manipulations, wide dynamic range compression was applied here to improve the audibility of soft sounds while ensuring loudness comfort for loud sounds. Performance in both speech intelligibility and BEG was measured in 13 HI listeners at three different masker levels and for different interaural stimulus manipulations. The results revealed that at low signal levels, performance substantially improved with increasing masker level, but this improvement was reduced by the compressive behaviour at higher levels. Moreover, artificially extending ILDs by applying infinite (broadband) ILDs provided an extra spatial benefit in speech reception thresholds of up to 5 dB on top of that already provided by natural ILDs and interaural time differences, which increased with increasing signal level.

Bilateral Versus Unilateral Cochlear Implantation in Adult Listeners: Speech-On-Speech Masking and Multitalker Localization.

Binaural hearing helps normal-hearing listeners localize sound sources and understand speech in noise. However, it is not fully understood how far this is the case for bilateral cochlear implant (CI) users. To determine the potential benefits of bilateral over unilateral CIs, speech comprehension thresholds (SCTs) were measured in seven Japanese bilateral CI recipients using Helen test sentences (translated into Japanese) in a two-talker speech interferer presented from the front (co-located with the target speech), ipsilateral to the first-implanted ear (at +90° or -90°), and spatially symmetric at ±90°. Spatial release from masking was calculated as the difference between co-located and spatially separated SCTs. Localization was assessed in the horizontal plane by presenting either male or female speech or both simultaneously. All measurements were performed bilaterally and unilaterally (with the first implanted ear) inside a loudspeaker array. Both SCTs and spatial release from masking were improved with bilateral CIs, demonstrating mean bilateral benefits of 7.5 dB in spatially asymmetric and 3 dB in spatially symmetric speech mixture. Localization performance varied strongly between subjects but was clearly improved with bilateral over unilateral CIs with the mean localization error reduced by 27°. Surprisingly, adding a second talker had only a negligible effect on localization.

Better-ear glimpsing at low frequencies in normal-hearing and hearing-impaired listeners.

Better-ear glimpsing is an auditory process that takes advantage of short-term interaural level differences (ILDs) to improve the understanding of speech in spatial fluctuating noise. Since ILDs are mainly present at high frequencies, where most hearing-impaired (HI) listeners have the strongest hearing loss, HI individuals cannot fully utilize ILDs for better-ear glimpsing, which may lead to poorer understanding of speech in noise. This problem may be alleviated by hearing aids that artificially generate ILDs at low frequencies where hearing is typically less impaired. The present study therefore investigated the spatial benefit in speech intelligibility that is provided by better-ear glimpsing with low-frequency extended ILDs in a symmetric two-distractor speech background. Speech reception thresholds were measured in a spatially co-located and separated condition as a function of frequency region in ten normal-hearing (NH) and ten mild-to-moderate sensorineural HI subjects. In both groups the extended ILDs provided a substantial spatial advantage on top of the advantage already provided by natural ILDs. Moreover, the spatial advantage was largely independent of frequency region, suggesting that both NH and HI subjects can utilize low-frequency ILDs for improving speech understanding in noise. Overall performance as well as spatial advantage was reduced in the HI group.