Effects of Head Movements on Sound-Source Localization in Single-Sided Deaf Patients With Their Cochlear Implant On Versus Off

Abstract

Objectives-We investigated the ability of single-sided deaf listeners implanted with a cochlear implant (SSD-CI) to (i) determine the front-back and left-right location of sound sources presented from loudspeakers surrounding the listener and (ii) use small head rotations to further improve their localization performance. The resulting behavioral data were used for further analyses investigating the value of so-called "monaural" spectral shape cues for front-back sound source localization.Design-Eight SSD-CI patients were tested with their CI on and off. Eight NH listeners, with one ear plugged during the experiment, and another group of eight NH listeners, with neither ear plugged, were also tested. Gaussian noises of three-second duration were bandpass filtered to 2-8 kHz and presented from one of six loudspeakers surrounding the listener, spaced 60° apart. Perceived sound source localization was tested under conditions where the patients faced forward with the head stationary, and under conditions where they rotated their heads between ±30°. Results-(i)Under stationary listener conditions, unilaterally-plugged NH listeners and SSD-CI listeners (with their CIs both on and off) were nearly at chance in determining the front-back location of high-frequency sound sources. (ii) Allowing rotational head movements improved performance in both the front-back and left-right dimensions for all listeners. (iii) For SSD-CI patients with their CI turned off, head rotations substantially reduced front-back reversals, and the combination of turning on the CI with head rotations led to near-perfect resolution of front-back sound source location. (iv) Turning on the CI also improved left-right localization performance. (v) As expected, NH listeners with both ears unplugged localized to the correct front/back and leftright hemifields both with and without head movements.Conclusions-Although SSD-CI listeners demonstrate a relatively poor ability to distinguish the front-back location of sound sources when their head is stationary, their performance is substantially improved with head movements. Most of this improvement occurs when the CI is off, suggesting that the NH ear does most of the "work" in this regard, though some additional gain is introduced with turning the CI on. During head turns, these listeners appear to primarily rely on comparing changes in head position to changes in monaural level (ML) cues produced by the direction-dependent attenuation of high-frequency sounds that result from acoustic head

Dynamic spectral cues do not affect human sound localization during small head movements

“…In a monaural listening experiment, normal-hearing listeners with one ear plugged showed no benefit of head rotations when localizing sounds located in the horizontal plane (Hirahara et al, 2021). However, single-sided deaf listeners do appear to utilize and even rely on changes in head position to induce changes in the monaural cues produced by the direction-dependent high-frequency attenuation resulting from acoustic head shadowing (Pastore et al, 2020).…”

Effects of Age at Implantation on Outcomes of Cochlear Implantation in Children with Short Durations of Single-Sided Deafness

“…Evidence from individuals with bimodal hearing through a CI and a hearing aid indicate large mismatches in place, level, and timing of interaural stimulation that are the likely cause of continuing deficits in binaural/spatial hearing in bimodal users ( 20 – 22 ). The localization of both stationary and moving sound appears to improve slightly, but significantly, with CI use in adult SSD users ( 23 , 24 ), and discrimination of front versus back sounds can be improved with head movement ( 25 ). Less is known about the effects of CI use on spatial hearing in children with SSD.…”

Proficiency in Using Level Cue for Sound Localization Is Related to the Auditory Cortical Structure in Patients With Single-Sided Deafness

“…However, reported data also show considerable variability in the degree to which localization accuracy is affected by monaural hearing, suggesting the adaptive contribution of the monaural level cues and monaural pinna cues, which normally play a minor role. For example, relatively good localization has been found in some adults with various degrees of unilateral hearing loss, whereas others cannot localize at all ( Slattery and Middlebrooks, 1994 ; Van Wanrooij, 2004 ; Shub et al, 2008 ; Agterberg et al, 2012 ; Firszt et al, 2017 ; Pastore et al, 2020 ). The variable impact of hearing loss on localization ability, even in individuals with unilateral sensorineural single-sided deafness (SSD), indicates that hearing loss in the poorer ear alone does not eradicate the potential to localize sound.…”

“…Deprived of binaural difference cues, the adaptive change in SSD would rely on increased proficiency of using remaining monaural spatial cues. Monaural level cues are primarily used over monaural spectral shape cues ( Shub et al, 2008 ; Pastore et al, 2020 ). Although inherently ambiguous, the monaural level cue can serve as a valid cue to azimuth because the learned sound will appear louder when presented on the better-hearing side ( Agterberg et al, 2012 ).…”