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While considerable evidence suggests that bilateral cochlear implant (CI) users' sound localization abilities rely primarily on interaural level difference (ILD) cues, and only secondarily, if at all, on interaural time difference (ITD) cues, this evidence has largely been indirect. This study used head-related transfer functions (HRTFs) to indepen...
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... DC testing, there were three conditions: (1) both ITD and ILD cues present ITD+ ILD, (2) only ITD cues present (ITD-only), and (3) only ILD cues present (ILD- only). Four additional bilateral CI users completed only the ITD+ ILD condition as well as SF test- ing (see Table 1 for listener details). Participants were assigned identifiers using the following con- This participant originally was implanted on the right side 3 years before testing, but electrodes started turning on and off unpredictably within 3 months, and the device was replaced approximately 1 year before testing. ...
Similar publications
Cochlear implantation successfully improves hearing in most adult recipients. However, in rare cases, post-implant rehabilitation is required to maximize benefit. The primary aim of this investigation was to test if self-reports by cochlear implant users indicate the need for post-implant rehabilitation. Listening performance was assessed with the...
Citations
... Van Hoesel et al., 2003). Probably, bilateral CI users use interaural level differences (ILDs) to obtain this benefit, as the perception of interaural time differences with current CI technology is severely limited (Aronoff et al., 2010). In music-related experiments, Vannson et al. (2015) investigated the perception of dichotic, diotic, and monaural presentation of piano pieces for bilateral CI users. ...
For people with profound hearing loss, a cochlear implant (CI) is able to provide access to sounds that support speech perception. With current technology, most CI users obtain very good speech understanding in quiet listening environments. However, many CI users still struggle when listening to music. Efforts have been made to preprocess music for CI users and improve their music enjoyment. This work investigates potential modifications of instrumental music to make it more accessible for CI users. For this purpose, we used two datasets with varying complexity and containing individual tracks of instrumental music. The first dataset contained trios and it was newly created and synthesized for this study. The second dataset contained orchestral music with a large number of instruments. Bilateral CI users and normal hearing listeners were asked to remix the multitracks grouped into melody, bass, accompaniment, and percussion. Remixes could be performed in the amplitude, spatial, and spectral domains. Results showed that CI users preferred tracks being panned toward the right side, especially the percussion component. When CI users were grouped into frequent or occasional music listeners, significant differences in remixing preferences in all domains were observed.
... This was achieved by having participants subjectively center example stimuli [33]. The presence of even a "zero magnitude" ILD likely influenced lateralization, as ILDs appear to be the dominant cue for localization and lateralization for CI listeners [6,41,42]. It will be important to consider the interactions of ILDs and ITDs, as the mixed-rate strategy, for example, does not currently explicitly encode ILDs on its low-rate channels but may introduce ILDs in the envelopes of all channels. ...
Background/Objective: Bilaterally implanted cochlear implant (CI) users do not consistently have access to interaural time differences (ITDs). ITDs are crucial for restoring the ability to localize sounds and understand speech in noisy environments. Lack of access to ITDs is partly due to lack of communication between clinical processors across the ears and partly because processors must use relatively high rates of stimulation to encode envelope information. Speech understanding is best at higher stimulation rates, but sensitivity to ITDs in the timing of pulses is best at low stimulation rates. Methods: We implemented a practical “mixed rate” strategy that encodes ITD information using a low stimulation rate on some channels and speech information using high rates on the remaining channels. The strategy was tested using a bilaterally synchronized research processor, the CCi-MOBILE. Nine bilaterally implanted CI users were tested on speech understanding and were asked to judge the location of a sound based on ITDs encoded using this strategy. Results: Performance was similar in both tasks between the control strategy and the new strategy. Conclusions: We discuss the benefits and drawbacks of the sound coding strategy and provide guidelines for utilizing synchronized processors for developing strategies.
... A cochlear implant (CI) can partially compensate for asymmetrical hearing and thus restore localization to some degree [Van Hoesel and Tyler, 2003;Ching et al., 2004;Seeber et al., 2004;Dunn et al., 2008;Grossmann et al., 2016;Dillon et al., 2017aDillon et al., , 2017b. Evidence suggests that bilateral CI users rely mostly on ILD [Van Hoesel and Tyler, 2003;Seeber and Fastl, 2008;Dorman et al., 2015], and their ITD sensitivity is generally supposed to be poor [Van Hoesel et al., 2009;Aronoff et al., 2010]. However, a role of the envelope ITD processing in spatial hearing with a CI is possible [Noel and Eddington, 2013;Todd et al., 2019] since envelope ITD cues are preserved during CI preprocessing. ...
b> Introduction: Spatial hearing is most accurate using both ears, but accuracy decreases in persons with asymmetrical hearing between ears. In participants with deafness in one ear but normal hearing in the other ear (single-sided deafness [SSD]), this difference can be compensated by a unilateral cochlear implant (CI). It has been shown that a CI can restore sound localization performance, but it is still unclear to what extent auditory spatial discrimination can be improved. Methods: The present study investigated auditory spatial discrimination using minimum audible angles (MAAs) in 18 CI-SSD participants. Results were compared to 120 age-matched normal-hearing (NH) listeners. Low-frequency (LF) and high-frequency (HF) noise bursts were presented from 4°, 30°, and 60° azimuth on the CI side and on the NH side. MAA thresholds were tested for correlation with localization performance in the same participants. Results: There were eight good performers and ten poor performers. There were more poor performers for LF signals than for HF signals. Performance on the CI side was comparable to performance on the NH side. Most difficulties occurred at 4° and at 30°. Eight of the good performers in the localization task were also good performers in the MAA task. Only the localization ability at 4° on the CI side was positively correlated with the MAA at that location. Conclusion: Our data suggest that a CI can restore localization ability but not necessarily auditory spatial discrimination at the same time. The ability to discriminate between adjacent locations may be trainable during rehabilitation to enhance important auditory skills.
... or TMR, is better in one ear than the other), binaural summation (where the redundant binaural representation allows for better segregation of the target), and binaural squelch (where the addition of the ear with the poorer TMR improves performance over the better ear alone) 26 . In general, bimodal hearing may not preserve important ITDs and/or ILDs due to timing differences (e.g., different compression time constants) between the acoustic hearing ear and the CI ear [27][28][29][30] . For many Bimodal CI patients, residual hearing in the contralateral ear provides only limited information due to the severity of underlying hearing loss. ...
Bimodal cochlear implant (CI) listeners have difficulty utilizing spatial cues to segregate competing speech, possibly due to tonotopic mismatch between the acoustic input frequency and electrode place of stimulation. The present study investigated the effects of tonotopic mismatch in the context of residual acoustic hearing in the non-CI ear or residual hearing in both ears. Speech recognition thresholds (SRTs) were measured with two co-located or spatially separated speech maskers in normal-hearing adults listening to acoustic simulations of CIs; low frequency acoustic information was available in the non-CI ear (bimodal listening) or in both ears. Bimodal SRTs were significantly better with tonotopically matched than mismatched electric hearing for both co-located and spatially separated speech maskers. When there was no tonotopic mismatch, residual acoustic hearing in both ears provided a significant benefit when maskers were spatially separated, but not when co-located. The simulation data suggest that hearing preservation in the implanted ear for bimodal CI listeners may significantly benefit utilization of spatial cues to segregate competing speech, especially when the residual acoustic hearing is comparable across two ears. Also, the benefits of bilateral residual acoustic hearing may be best ascertained for spatially separated maskers.
... Acoustic-hearing listeners are also sensitive to ITD in the temporal envelope (ENV-ITD), particularly when no usable ITD is present in the temporal fine structure (FS-ITDs) (Henning, 1974;Bernstein and Trahiotis, 2002;Bernstein and Trahiotis, 2012). ENV-ITDs are of particular interest to those studying spatial hearing in bilateral cochlear-implant (BiCI) listeners, as clinical cochlear-implant processing typically discards temporal fine structure leaving only the temporal envelope, therefore precluding access to low-frequency FS-ITDs but potentially preserving access to ILDs and ENV-ITDs (Aronoff et al., 2010;Grantham et al., 2008). ...
Interaural time differences (ITDs), an important acoustic cue for perceptual sound-source localization, are conventionally modeled as monotonic functions of azimuth. However, recent literature and publicly available databases from binau-ral manikins demonstrated ITDs conveyed by the envelopes (ENV-ITDs) of high-frequency (!2 kHz) signals that were non-monotonic functions of azimuth. This study demonstrates using a simple, time-dependent geometric model of an elliptic head that the back-traveling (longer) sound path around the head, delayed and added to the conventionally treated front-traveling path, can account for non-monotonic ENV-ITDs. These findings have implications for spatial-hearing models in acoustic and electric (cochlear-implant) hearing. V C 2023 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license
... In contrast to NH listeners, bilateral cochlear-implant (BiCI) listeners do not reach the same level of sound localization performance and may rely primarily on ILDs when locating sound sources in free field (Aronoff et al., 2010;Grantham et al., 2007). One reason for the gap in performance is that when listening through clinical processors, BiCI listeners are unable to access ITDs for low-rate signals, which is typically conveyed through the carrier frequencies of a modulated speech signal, or "temporal fine structure" (TFS) of an acoustic signal (Dennison et al., 2022). ...
While listeners with bilateral cochlear implants (BiCIs) are able to access information in both ears, they still struggle to perform well on spatial hearing tasks when compared to normal hearing listeners. This performance gap could be attributed to the high stimulation rates used for speech representation in clinical processors. Prior work has shown that spatial cues, such as interaural time differences (ITDs), are best conveyed at low rates. Further, BiCI listeners are sensitive to ITDs with a mixture of high and low rates. However, it remains unclear whether mixed-rate stimuli are perceived as unitary percepts and spatially mapped to intracranial locations. Here, electrical pulse trains were presented on five, interaurally pitch-matched electrode pairs using research processors, at either uniformly high rates, low rates, or mixed rates. Eight post-lingually deafened adults were tested on perceived intracranial lateralization of ITDs ranging from 50 to 1600 μs. Extent of lateralization depended on the location of low-rate stimulation along the electrode array: greatest in the low- and mixed-rate configurations, and smallest in the high-rate configuration. All but one listener perceived a unitary auditory object. These findings suggest that a mixed-rate processing strategy can result in good lateralization and convey a unitary auditory object with ITDs.
... The physical alignment of these frequency channels across the ears is usually only an approximation (Goupell et al., 2022). Furthermore, due to the nature of the signal processing in today's CIs, fine temporal detail is generally unavailable, and BI-CI listeners appear to primarily use interaural level differences rather than ITDs for sound localization when using clinical processors (Aronoff et al., 2010;Seeber & Fastl, 2008;van Hoesel & Tyler, 2003). ...
Sensitivity to interaural time differences (ITDs) in acoustic hearing involves comparison of interaurally frequency-matched inputs. Bilateral cochlear-implant arrays are, however, only approximately aligned in angular insertion depth and scalar location across the cochleae. Interaural place-of-stimulation mismatch therefore has the potential to impact binaural perception. ITD left-right discrimination thresholds were examined in 23 postlingually-deafened adult bilateral cochlear-implant listeners, using low-rate constant-amplitude pulse trains presented via direct stimulation to single electrodes in each ear. Angular insertion depth and scalar location measured from computed-tomography (CT) scans were used to quantify interaural mismatch, and their association with binaural performance was assessed. Number-matched electrodes displayed a median interaural insertion-depth mismatch of 18° and generally yielded best or near-best ITD discrimination thresholds. Two listeners whose discrimination thresholds did not show this pattern were confirmed via CT to have atypical array placement. Listeners with more number-matched electrode pairs located in the scala tympani displayed better thresholds than listeners with fewer such pairs. ITD tuning curves as a function of interaural electrode separation were broad; bandwidths at twice the threshold minimum averaged 10.5 electrodes (equivalent to 5.9 mm for a Cochlear-brand pre-curved array). Larger angular insertion-depth differences were associated with wider bandwidths. Wide ITD tuning curve bandwidths appear to be a product of both monopolar stimulation and angular insertion-depth mismatch. Cases of good ITD sensitivity with very wide bandwidths suggest that precise matching of insertion depth is not critical for discrimination thresholds. Further prioritizing scala tympani location at implantation should, however, benefit ITD sensitivity.
... Literature comparing spatial hearing ability between CI users and NH participants have only compared NH controls with bilateral CI users and showed a superior ability and better reports of spatial hearing (Kan & Litovsky, 2015). A theory to explain why sound localization is difficult for CI users is that to judge the location of a sound, NH individuals use interaural level differences (ILD) combined with interaural time differences (ITD), however, studies have shown CI users to rely more on the former than the latter (Aronoff et al., 2010Grantham et al., 2007;Seeber & Fastl, 2008;van Hoesel & Tyler, 2003). In a study paradigm where participants simply had to indicate the direction of a . ...
... This suggests that the spatial advantage that a second CI provides, allows for an increase in working memory ability and a better ability to perceive speech. Although it is beneficial to have a second CI, their spatial and speech perception performance compared to NH individuals is still weaker and they use more cognitive resources due to differences in encoding spatially distinct information (Aronoff et al., 2010Grantham et al., 2007;Kan & Litovsky, 2015;Paul et al., 2020;Seeber & Fastl, 2008;van Hoesel & Tyler, 2003) Future longitudinal studies on the cognitive effects of using bilateral versus unilateral CIs and compared to NH individuals are required to investigate the possible cognitive consequences of not obtaining a second CI and to see if bilateral CI users still present a pattern of cognitive decline and dementia later in life so commonly found in individuals with hearing loss Lin, Thorpe, et al., 2011;Livingston et al., 2017;Lopes et al., 2007;Slade et al., 2020). If that is that case then interventions involving the improvement of working memory and cognitive abilities in CI users, would possibly result in better outcomes and protection against cognitive decline. ...
A common concern in individuals with cochlear implants (CIs) is difficulty following conversations in noisy environments and social settings. The ability to accomplish these listening tasks relies on the individual working memory abilities and draws upon limited cognitive resources to accomplish successful listening. For some individuals, allocating too much, can result deficits in speech perception and in long term detriments of quality of life. For this study, 31 CI users and NH controls completed a series of online behavioural tests and quality of life surveys, in order to investigate the relationship between visual and auditory working memory, clinical and behavioural measures of speech perception and quality of life and hearing. Results showed NH individuals were superior on auditory working memory and survey outcomes. In CI users, recall performance on the three working memory span tests declined from visual reading span to auditory listening in quiet and then listening in noise and speech perception was predictably worse when presented with noise maskers. Bilateral users performed better on each task compared to unilateral/HA and unilateral only users and reported better survey outcomes. Correlation analysis revealed that memory recall and speech perception ability were significantly correlated with sections of CIQOL and SSQ surveys along with clinical speech perception scores in CI users. These results confirm that hearing condition can predict working memory and speech perception and that working memory ability and speech perception, in turn, predict quality of life. Importantly, we demonstrate that online testing can be used as a tool to assess hearing, cognition, and quality of life in CI users.
... Cochlear implants (CIs) have become standard intervention for neurosensory deafness (Moore & Shannon 2009;Wilson 2019). Bilateral CIs (BCIs) are increasingly common, thus allowing partial access to interaural auditory cues (Aronoff et al. 2010;Gifford & Stecker 2020). Benefits of CIs for speech understanding are now well-established in children (Allen et al. 1998;Calmels et al. 2004), adults (Wilson et al. 1991;Stickney et al. 2004;Wilson 2017), and aging individuals (Forli et al. 2019). ...
Objectives:
We assessed if spatial hearing training improves sound localization in bilateral cochlear implant (BCI) users and whether its benefits can generalize to untrained sound localization tasks.
Design:
In 20 BCI users, we assessed the effects of two training procedures (spatial versus nonspatial control training) on two different tasks performed before and after training (head-pointing to sound and audiovisual attention orienting). In the spatial training, participants identified sound position by reaching toward the sound sources with their hand. In the nonspatial training, comparable reaching movements served to identify sound amplitude modulations. A crossover randomized design allowed comparison of training procedures within the same participants. Spontaneous head movements while listening to the sounds were allowed and tracked to correlate them with localization performance.
Results:
During spatial training, BCI users reduced their sound localization errors in azimuth and adapted their spontaneous head movements as a function of sound eccentricity. These effects generalized to the head-pointing sound localization task, as revealed by greater reduction of sound localization error in azimuth and more accurate first head-orienting response, as compared to the control nonspatial training. BCI users benefited from auditory spatial cues for orienting visual attention, but the spatial training did not enhance this multisensory attention ability.
Conclusions:
Sound localization in BCI users improves with spatial reaching-to-sound training, with benefits to a nontrained sound localization task. These findings pave the way to novel rehabilitation procedures in clinical contexts.
... Despite this improvement, front-back discrimination remained difficult for CI users, partly due to the lack of salient ITD cues (Aronoff et al. 2010;see Laback et al. 2015 for review). Some authors suggest that the fine-structure temporal processing implemented in some processors (e.g., FS4 in MED-EL) improves ITD cues and helps patients with some auditory skills (e.g., music perception, Roy et al. 2015). ...
Objective:
The aim of this study was to evaluate the feasibility of a virtual reality-based spatial hearing training protocol in bilateral cochlear implant (CI) users and to provide pilot data on the impact of this training on different qualities of hearing.
Design:
Twelve bilateral CI adults aged between 19 and 69 followed an intensive 10-week rehabilitation program comprised eight virtual reality training sessions (two per week) interspersed with several evaluation sessions (2 weeks before training started, after four and eight training sessions, and 1 month after the end of training). During each 45-minute training session, participants localized a sound source whose position varied in azimuth and/or in elevation. At the start of each trial, CI users received no information about sound location, but after each response, feedback was given to enable error correction. Participants were divided into two groups: a multisensory feedback group (audiovisual spatial cue) and an unisensory group (visual spatial cue) who only received feedback in a wholly intact sensory modality. Training benefits were measured at each evaluation point using three tests: 3D sound localization in virtual reality, the French Matrix test, and the Speech, Spatial and other Qualities of Hearing questionnaire.
Results:
The training was well accepted and all participants attended the whole rehabilitation program. Four training sessions spread across 2 weeks were insufficient to induce significant performance changes, whereas performance on all three tests improved after eight training sessions. Front-back confusions decreased from 32% to 14.1% (p = 0.017); speech recognition threshold score from 1.5 dB to -0.7 dB signal-to-noise ratio (p = 0.029) and eight CI users successfully achieved a negative signal-to-noise ratio. One month after the end of structured training, these performance improvements were still present, and quality of life was significantly improved for both self-reports of sound localization (from 5.3 to 6.7, p = 0.015) and speech understanding (from 5.2 to 5.9, p = 0.048).
Conclusions:
This pilot study shows the feasibility and potential clinical relevance of this type of intervention involving a sensorial immersive environment and could pave the way for more systematic rehabilitation programs after cochlear implantation.
