Two groups of children will be included: Group 1 will include prelingiustic deaf children ages 18 months - 5 years and Group 2 will include postlinguistic deaf children < 21 years of age. Post-operative evaluations will be conducted at the initial activation and at 1, 3, 6, 12, 18, 24, 30, and 36-month intervals post-activation in order to demonstrate the emergence of open-set speech perception abilities prior to study cessation. Experience in the CI literature has shown that a minimum of 2 years of device usage is required for children with pre-lingual hearing impairment to develop some open-set speech perception abilities. While Group 2 is post-linguistic and some may have had significant hearing prior to becoming deaf, the same time intervals will be used for consistency. Blinding or masking procedures are not included in the design, as the presence/absence of a brainstem implant cannot be easily concealed from the device recipients and/or clinical investigators.