Single-sided deafness and directional hearing: contribution of spectral cues and high-frequency hearing loss in the hearing ear

Abstract

Direction-specific interactions of sound waves with the head, torso, and pinna provide unique spectral-shape cues that are used for the localization of sounds in the vertical plane, whereas horizontal sound localization is based primarily on the processing of binaural acoustic differences in arrival time (interaural time differences, or ITDs) and sound level (interaural level differences, or ILDs). Because the binaural sound-localization cues are absent in listeners with total single-sided deafness (SSD), their ability to localize sound is heavily impaired. However, some studies have reported that SSD listeners are able, to some extent, to localize sound sources in azimuth, although the underlying mechanisms used for localization are unclear. To investigate whether SSD listeners rely on monaural pinna-induced spectral-shape cues of their hearing ear for directional hearing, we investigated localization performance for low-pass filtered (LP, <1.5 kHz), high-pass filtered (HP, >3kHz), and broadband (BB, 0.5–20 kHz) noises in the two-dimensional frontal hemifield. We tested whether localization performance of SSD listeners further deteriorated when the pinna cavities of their hearing ear were filled with a mold that disrupted their spectral-shape cues. To remove the potential use of perceived sound level as an invalid azimuth cue, we randomly varied stimulus presentation levels over a broad range (45–65 dB SPL). Several listeners with SSD could localize HP and BB sound sources in the horizontal plane, but inter-subject variability was considerable. Localization performance of these listeners strongly reduced after diminishing of their spectral pinna-cues. We further show that inter-subject variability of SSD can be explained to a large extent by the severity of high-frequency hearing loss in their hearing ear.

Bone conductive implants in single-sided deafness

“…When the first BCI was introduced into clinical practice for SSD, several studies investigated their performance compared to the CROS HA. In reality, the BCI would not restore binaural hearing but, by inducing a phase difference in bone conduction stimulation in the normal-hearing cochlea, it exceeds the disadvantages imposed by the head shadow effect, enhancing the monaural function of the healthy side [10]. Although speech discrimination in noise has been shown to be greatly improved compared with the CROS HA, no great differences were found in terms of improvement for sound localization.…”

Comparison of Speech-in-Noise and Localization Benefits in Unilateral Hearing Loss Subjects Using Contralateral Routing of Signal Hearing Aids or Bone-Anchored Implants

“…This is attributed to the head shadow effect and the resulting sound level differences that occur for sounds arriving at the impaired ear versus the normal hearing ear(18). Others have shown that some monaural listeners are able to use spectral cues to improve horizontal localization ability, although large inter-subject variability is observed(17). In our clinical experience we have observed that some monaural listeners will anecdotally report perceived localization ability.…”

“…Interestingly, others have demonstrated that monaural listeners can in fact localize in the horizontal plane by using either spectral cues(17) or perceived level differences in the signal as it moves from the impaired ear to the normal hearing ear(18). It is possible that with the increased audibility provided with CROS and BAIs, some localization ability may be restored.…”

Localization training results in individuals with unilateral severe to profound hearing loss

“…Where sound spectra are more diverse, spectral cues are less reliable, which leads to dependence on changes in proximal sound levels, or the much less precise head-shadow effects (Van Wanrooij and Van Opstal, 2004). In a study of adults with unilateral SPHL, Agterberg et al (2014) attributed much of the inter-subject variability for horizontal plane localization to the varying degrees of high frequency hearing in the better ear of participants. The participants with better high frequency hearing were also better able to use pinna-induced spectral-shape cues of the better hearing ear to aid sound localization.…”