Bilateral cochlear implants in children: Effects of auditory experience and deprivation on auditory perception

Abstract

Spatial hearing skills are essential for children as they grow, learn and play. They provide critical cues for determining the locations of sources in the environment, and enable segregation of important sources, such as speech, from background maskers or interferers. Spatial hearing depends on availability of monaural cues and binaural cues. The latter result from integration of inputs arriving at the two ears from sounds that vary in location. The binaural system has exquisite mechanisms for capturing differences between the ears in both time of arrival and intensity. The major cues that are thus referred to as being vital for binaural hearing are: interaural differences in time (ITDs) and interaural differences in levels (ILDs). In children with normal hearing (NH), spatial hearing abilities are fairly well developed by age 4–5 years. In contrast, children who are deaf and hear through cochlear implants (CIs) do not have an opportunity to experience normal, binaural acoustic hearing early in life. These children may function by having to utilize auditory cues that are degraded with regard to numerous stimulus features. In recent years there has been a notable increase in the number of children receiving bilateral CIs, and evidence suggests that while having two CIs helps them function better than when listening through a single CI, they generally perform worse than their NH peers. This paper reviews some of the recent work on bilaterally implanted children. The focus is on measures of spatial hearing, including sound localization, release from masking for speech understanding in noise and binaural sensitivity using research processors. Data from behavioral and electrophysiological studies are included, with a focus on the recent work of the authors and their collaborators. The effects of auditory plasticity and deprivation on the emergence of binaural and spatial hearing are discussed along with evidence for reorganized processing from both behavioral and electrophysiological studies. The consequences of both unilateral and bilateral auditory deprivation during development suggest that the relevant set of issues is highly complex with regard to successes and the limitations experienced by children receiving bilateral cochlear implants.

Unilateral Hearing Loss: Understanding Speech Recognition and Localization Variability—Implications for Cochlear Implant Candidacy

“…Whether later implantation of a congenital, unilaterally deaf ear is as viable as early implantation of that ear is unknown at this time. Bilaterally implanted children and adults with delayed second-ear implantation have reduced binaural benefits due to extended periods of unilateral hearing (Gordon et al 2013; Litovsky and Gordon 2016; Litovsky and Misurelli 2016; Ramsden et al 2005; Reeder et al 2016; Reeder et al 2014). Collectively, these studies suggest potential compromises to binaural benefits of cochlear implantation for individuals with prolonged unilateral deafness.…”

Simultaneous bilateral cochlear implants: Developmental advances do not yet achieve normal cortical processing

“…Although bilaterally implanted children derive significant benefit when using two CIs compared to one (Gordon & Papsin, 2009), their performance in certain binaural tasks remains poorer and/or abnormal compared to normal hearing children (Litovsky & Gordon, 2016;Steel, Papsin, & Gordon, 2015). The difficulty in integrating input from both ears may relate to factors such as representation of input from individual ears, deafness/hearing loss, hearing experience, and/or lack of integration between bilateral devices.…”

Microsecond Interaural Time Difference Discrimination Restored by Cochlear Implants After Neonatal Deafness

“…In contrast, the ITD sensitivity of CI patients is highly variable and generally very poor, even when tested with experimental processors capable of delivering synchronized stimulus pulses with sub-millisecond resolution [3,[5][6][7]10,11].The binaural performance of CI patients depends to a fair extent on the patients' history. Importantly, pre-lingually deaf CI users invariably appear to exhibit no ITD sensitivity at all, whereas many post-lingually deaf CI users do exhibit at least some degree of ITD sensitivity [4,5,[11][12][13]. This has led to the suggestion that early auditory deprivation during a sensitive period may prevent the development of ITD sensitivity, and that this cannot be recovered with later binaural stimulation using state-of-the-art speech processors [1,13,14].…”

“…Importantly, pre-lingually deaf CI users invariably appear to exhibit no ITD sensitivity at all, whereas many post-lingually deaf CI users do exhibit at least some degree of ITD sensitivity [4,5,[11][12][13]. This has led to the suggestion that early auditory deprivation during a sensitive period may prevent the development of ITD sensitivity, and that this cannot be recovered with later binaural stimulation using state-of-the-art speech processors [1,13,14]. If that hypothesis is correct, then developing more sophisticated binaural CI processors might not benefit the many patients who are born deaf or lose their hearing very early in life.…”