Bimodal Hearing or Bilateral Cochlear Implants: A Review of the Research Literature

Carol A Sammeth; Sean M Bundy; Douglas A Miller

doi:10.1055/s-0031-1271945

Seminars in Hearing, Table of Contents

Semin Hear 2011; 32(1): 003-031
DOI: 10.1055/s-0031-1271945

Bimodal Hearing or Bilateral Cochlear Implants: A Review of the Research Literature

Carol A. Sammeth¹ ^, ² , Sean M. Bundy¹ , Douglas A. Miller³

¹Cochlear Americas, Centennial, Colorado
²Division of Speech, Language, and Hearing Sciences, University of Colorado, Boulder, Colorado
³Department of Electrical and Computer Engineering, University of Denver, Denver, Colorado

Abstract

ABSTRACT

Over the past 10 years, there have been an increasing number of patients fitted with either bimodal hearing devices (unilateral cochlear implant [CI], and hearing aid on the other ear) or bilateral cochlear implants. Concurrently, there has been an increasing interest in and number of publications on these topics. This article reviews the now fairly voluminous research literature on bimodal hearing and bilateral cochlear implantation in both children and adults. The emphasis of this review is on more recent clinical studies that represent current technology and that evaluated speech recognition in quiet and noise, localization ability, and perceived benefit. A vast majority of bilaterally deaf subjects in these studies showed benefit in one or more areas from bilateral CIs compared with listening with only a unilateral CI. For patients who have sufficient residual low-frequency hearing sensitivity for the provision of amplification in the nonimplanted ear, bimodal hearing appears to provide a good nonsurgical alternative to bilateral CIs or to unilateral listening for many patients.

KEYWORDS

Bimodal hearing - bimodal devices - bilateral cochlear implants - binaural hearing

Full Text

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1 However, Christopher Long, Ph.D., of Cochlear Americas, notes that such binaural effects are not necessarily indicative of particular mechanisms (personal communication, 2009). For example, dichotic speech cue summation (i.e., processors using interleaved frequency bands on the two sides) would not be expected to give binaural decorrelation benefit, but could still give benefits beyond head shadow and binaural redundancy effects. Also, a listener with patchy nerve survival may hear different cues in each ear across SNRs, but this would not be detected by a simple binaural redundancy test. Thus, it is still debatable whether “true” binaural processing effects are being measured with today's CIs, especially because ITD (interaural timing difference) sensitivity is likely the source of binaural “unmasking” yet these cues are often blurred by the sound processing. Although this is an important academic discussion, for purposes of this article, the focus will not be on the source of bilateral benefits, but simply whether or not they are reported using traditional measurements.

2 Although occasionally authors have referred to the bimodal hearing configuration as “electric-acoustic hearing,” that term will not be used herein because it can also mean stimulation with investigational hybrid devices currently in development but not yet approved for marketing. In hybrid devices, like in bimodal hearing, both electric (CI) and acoustic (HA) hearing are provided; however, in the case of hybrid devices, both are provided to the same ear, rather than opposite ears as in bimodal hearing.

3 Note that studies that directly compared performance of a group of subjects with bimodal hearing with a group subjects with bilateral CIs are reviewed later in this article.

4 Internal Cochlear estimates are that, of the more than 140,000 recipients of Nucleus CIs worldwide, less than 10% are currently implanted bilaterally.

5 Although from a future research perspective, it will be important to determine what cues provide benefits and which are lost, to assist in improving future outcomes with new sound processing approaches.

6 Nevertheless, these researchers recommended an intersurgery interval in postlingual adults of no more than 12 years and noted that in children a longer interval may result in the need for additional rehabilitation to avoid refusal of the second implant. The value of 12 years may be arguable based on research showing benefit with even longer periods of auditory deprivation.

Carol A SammethPh.D.

Senior Regulatory/Clinical Specialist, Cochlear Americas

13059 East Peakview Avenue, Centennial, CO 80111

Email: csammeth@cochlear.com