A prospective, randomized study of cochlear implants. The Department of Veterans Affairs Cochlear Implant Study Group

Cochlear implants restore some degree of hearing in patients with severe hearing impairment, but the efficacy of different implants has not been compared. We conducted a prospective trial to compare several cochlear implants.

We studied 82 patients who were randomly assigned to receive one of three cochlear implants: the Ineraid multichannel implant (implant 1), the Nucleus multichannel implant (implant 2), and the 3M/Vienna single-channel implant (implant 3). All the patients had profound deafness, and none had derived benefit from hearing aids. The assigned device was successfully implanted in 80 patients. Twenty-four hearing tests were used to assess the patients' performance before implantation and 12 and 24 months after implantation. The tests were grouped into five categories according to their content, and a weighted composite index was developed to provide a single numerical indicator of the overall auditory response.

All the patients were able to hear with their implants. Nineteen of the 30 patients (63 percent) who received implant 2, 18 of the 30 patients (60 percent) who received implant 1, and 1 of the 20 patients (5 percent) who received implant 3 were able to distinguish some words and sentences. The scores for the composite index were similar in the patients who received implant 1 and those who received implant 2, and were higher in both these groups than in the patients who received implant 3 (P = 0.02). When 24 patients with implant 2 were given an improved speech processor, their composite index increased significantly within 3 months (P < 0.001); their score at that time was also significantly higher (P = 0.04) than the score of the patients with implant 1 at 24 months. Age at implantation, lip-reading ability, and IQ were prognostic indicators of the patients' performance with a cochlear implant.

Multichannel cochlear implants are superior to single-channel implants, especially for understanding speech. Changes in speech processing can improve patients' performance.