Auditory brainstem implant  An auditory brainstem implant (ABI) is a surgically implanted electronic device that provides a sense of sound to a person who is profoundly deaf, due to retrocochlear hearing impairment (due to illness or injury damaging the cochlea or auditory nerve, and so precluding the use of a cochlear implant). In Europe, ABIs have been used in children and adults, and in patients with neurofibromatosis type II.