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Literature Review: A Roundup of Important Recent Studies

Bilateral Cochlear Implants Improve Spatial Acuity

Can bilateral cochlear implantation, provided at a time of neural plasticity, produce normal or near-normal spatial hearing skills in young children?

Background: Spatial hearing skills improve speech understanding, especially in the presence of background noise. Children entirely dependent on unilateral cochlear implants do not develop significant sound localization skills compared with normal hearing children. Preliminary data suggest that early implantation with bilateral cochlear implants, either in a simultaneous or sequential fashion, allows users to develop better sound localization skills.

Study design: Prospective comparison of three groups of children aged 26 to 36 months: 1) normal hearing controls; 2) unilateral cochlear implant users and 3) bilateral cochlear implant users. Testing compared patients in their ability to identify the minimal audible angle of a sound source varied by 10 degrees. In addition, the unilateral cochlear implant users were compared with the bilateral cochlear implant users in correction identification of a sound source with a fixed angle of +/- 50 degrees.

Setting: Academic medical center: Waisman Center, University of Wisconsin-Madison.

Synopsis: Eight children with normal hearing (NH), 12 with a unilateral cochlear implant (UCI), and 27 with bilateral cochlear implants (BICI) were tested for minimal audible angle (MAA) using an array of speakers placed at 10-degree intervals and spanning 140 degrees of arc. The group of children with normal hearing had an MAA with a mean of 14.5 degrees and a range of 3.3 to 30.2 degrees. UCI children could not reach a minimum correct score at any one angle and the MAA could not be calculated. BICI children had an MAA of 30.9 degrees (range 5.7 to 69.6 degrees). For the fixed angle experiment, UCI children performed at chance and BICI children performed at one standard deviation above chance in correctly identifying a right-left discrimination with a speaker fixed at +/- 50 degrees.

In this age group, BICI children performed better than UCI children in these spatial acuity tasks. The BICI children did not perform as well as normal hearing controls. The cochlear implant children in general used a microphone placement behind the ear. For the BICI children, the signal for each device was independently controlled; there is not a commercially available binaural processor that can preserve interaural level or timing differences, which could theoretically improve performance in this task.