Binaural interactions develop in the auditory brainstem of children who are deaf: Effects of place and level of bilateral electrical stimulation

Abstract

Bilateral cochlear implants (CIs) might promote development of binaural hearing required to localize sound sources and hear speech in noise for children who are deaf. These hearing skills improve in children implanted bilaterally but remain poorer than normal. We thus questioned whether the deaf and immature human auditory system is able to integrate input delivered from bilateral CIs. Using electro-physiologicalmeasuresofbrainstem activity that includethe Binaural Difference(BD),ameasureofbinaural processing,weshowed that a period of unilateral deprivation before bilateralCI use prolonged response latencies but that amplitudes were not significantly affected. Tonotopic organization was retained to some extent as evidenced by an elimination of the BD with large mismatches in place of stimulation between the two CIs. Smaller place mismatches did not affect BD latency or amplitude, indicating that the tonotopic organization of the auditory brainstemisunderdeveloped and/or not wellusedbyCIstimulation. Finally,BDamplitudes decreased whenthe intensity of bilateral stimulation became weighted to one side and this corresponded to a perceptual shift of sound away from midline toward the side of increased intensity. In summary, bilateral CI stimulation is processed by the developing human auditory brainstem leading to perceptual changes in sound location and potentially improving hearing for children who are deaf. © 2012 the authors.