A review of the effects of unilateral hearing loss on spatial hearing

Abstract

The capacity of the auditory system to extract spatial information relies principally on the detection and interpretation of binaural cues, i.e., differences in the time of arrival or level of the sound between the two ears. In this review, we consider the effects of unilateral or asymmetric hearing loss on spatial hearing, with a focus on the adaptive changes in the brain that may help to compensate for an imbalance in input between the ears. Unilateral hearing loss during development weakens the brain's representation of the deprived ear, and this may outlast the restoration of function in that ear and therefore impair performance on tasks such as sound localization and spatial release from masking that rely on binaural processing. However, loss of hearing in one ear also triggers a reweighting of the cues used for sound localization, resulting in increased dependence on the spectral cues provided by the other ear for localization in azimuth, as well as adjustments in binaural sensitivity that help to offset the imbalance in inputs between the two ears. These adaptive strategies enable the developing auditory system to compensate to a large degree for asymmetric hearing loss, thereby maintaining accurate sound localization. They can also be leveraged by training following hearing loss in adulthood. Although further research is needed to determine whether this plasticity can generalize to more realistic listening conditions and to other tasks, such as spatial unmasking, the capacity of the auditory system to undergo these adaptive changes has important implications for rehabilitation strategies in the hearing impaired.

Differential Adaptation in Azimuth and Elevation to Acute Monaural Spatial Hearing after Training with Visual Feedback

“…Under monaural hearing conditions, the binaural time- and level-differences are heavily perturbed or absent, which severely hampers azimuth localization (Oldfield and Parker, 1986; Moore et al, 1999; Kacelnik et al, 2006; Van Wanrooij and Van Opstal, 2007; Kumpik et al, 2010; Agterberg et al, 2012; Keating and King, 2013; Keating et al, 2016; Kumpik and King, 2019). Four additional cues could subserve azimuth localization under perturbed binaural hearing: (1) the level-related head-shadow effect (HSE), (2) weakened binaural level differences, (3) the spectral cues from the hearing ear, and (4) low-pass (LP) filtering by the head (Oldfield and Parker, 1986; Van Wanrooij and Van Opstal, 2007; Kumpik and King, 2019). Note that the monaural head-shadow cue is ambiguous, as a loud sound at the perturbed side may be perceived just as loud as a soft sound at the hearing side.…”

“…Therefore, the veridical location of the sound source cannot be specified by these monaural cues alone (Van Opstal, 2016). Yet, in familiar environments, or sounds with known properties, monaural listeners could use the HSE in combination with these priors to better estimate their location (Van Wanrooij and Van Opstal, 2007; Carlile, 2014; Van Opstal, 2016; Kumpik and King, 2019).…”

Listening-Related Fatigue in Children With Unilateral Hearing Loss

“…When children have UHL, however, these binaural cues are diminished, thus producing ripple effects that may impact areas such as education, speech recognition in noise, and language and cognitive skills. Other factors that might also contribute to the problems of children with UHL include changes in auditory and brain structures as a result of auditory deprivation, age of identification/intervention, degree of HL in the impaired ear, and our inability to identify "early on" those children at risk for academic and communicative difficulties (Fitzpatrick et al, 2019;Kumpik & King, 2019;Tharpe, 2008;van Wieringen et al, 2018).…”

Hearing with One Ear: Consequences and Treatments for Profound Unilateral Hearing Loss

“…The auditory system's ability to adapt to the lack of binaural cues to preserve spatial hearing abilities as much as possible is remarkable. This process is achieved by reweighting the available cues, exploiting the location-dependent monaural cues [32]. However, in a normal every-day acoustic scenario, sounds are constantly changing in level, location and frequency, which makes it impossible to have accurate spatial hearing based only on monaural cues.…”