An assembly of electronic devices intended to restore useful hearing to a deaf patient via electrical stimulation of the brainstem's cochlear nucleus. It typically includes an external speech processor and microphone/headset to transform acoustical signals into an electrical code, which is transmitted from the headset to a surgically implanted receiver-stimulator where it is decoded and delivered to a multichannel electrode array. The array is surgically placed on the cochlear nucleus, which when stimulated results in the signal's transmission to the brain where it is interpreted as sound. An auditory brainstem implant (ABI) is used to treat deafness resulting from auditory nerve tumours.