Electric-acoustic stimulation (hybrid CI)

Many candidates for implantation retain usable low-frequency acoustic hearing but have lost high-frequency hair cells. Electric-acoustic stimulation (EAS, hybrid cochlear implantation) preserves that residual low-frequency hearing in the implanted ear and combines it with electric stimulation of the high-frequency (basal) region, so the user hears acoustically below the cutoff and electrically above it. Preserved acoustic low frequencies deliver genuine temporal fine structure — hence better pitch, music, and speech-in-noise than an all-electric map.

EAS depends critically on atraumatic surgery: a short or flexible array, slow soft insertion, and often steroids are used to preserve the delicate apical cochlea. Hearing preservation nonetheless fails, partially or fully, in a substantial minority, sometimes months after an initially successful implant (progressive loss from fibrosis or ossification). EAS thus makes hearing preservation — and the biology of the cochlear response to a chronic foreign body — a central clinical concern rather than a niche one.