Sizing up implants that banish the silence.

"To be deaf is a greater affliction than to be blind." With those words Helen Keller, who was both deaf and blind, articulated the isolation that engulfs a person who has lost the ability to hear. For some profoundly deaf people, however, cochlear implants can pierce the silence.

Unlike hearing aids, which merely amplify sound, these implants transduce sound into electrical signals and deliver that message to the nerve cells near the cochlea, the spiral-shaped part of the inner ear. Thus cochlear implants can help deaf people who do not benefit from a hearing aid.

Yet, when it comes to picking the best implant for a particular patient, doctors had been reduced to a guessing game. A new study shows that a certain type of cochlear implant provides superior benefits for most profoundly deaf people.

There are two main types of cochlear implants. Multichannel devices rely on more than one electrode to stimulate discrete areas of the inner ear; single-channel implants employ just one electrode to send messages to all parts of the cochlea at once. Noel L. Cohen and Susan B. Waltzman of the New York University School of Medicine in New York City and their colleagues at seven Department of Veterans Affairs hospitals wanted to evaluate the efficacy of single-channel and multichannel cochlear implants.

They recruited 80 profoundly deaf people, all of whom had lost their hearing as adults. The team gave all recruits a battery of sophisticated hearing tests at the start of the study Then the researchers randomly assigned the participants to receive one of three brands of implants. Patients underwent an operation to implant the electrode part of their assigned device. After surgery, the recruits wore a headset that acts as a microphone and carried a portable sound processor about the size of a cigarette pack. At various points after the procedure, the researchers gave all participants the same hearing tests and noted any improvement.

The team discovered that all recruits could hear some sounds with their implants. However, people who received the multichannel implants proved more likely to experience significant improvement than those who got the single-channel model. Of the people who got the multichannel devices, 19 of 30 (63 percent) who got one model and 18 of 30 (60 percent) who received a second model could distinguish some words and sentences. By contrast, just one of 20 patients (5 percent) who got the single-channel model could do the same. The team reports its findings in the Jan. 28 NEW ENGLAND JOURNAL OF MEDICINE.

People who gained the most from the implants went from nearly complete deafness to an ability to hear people talking on the telephone, a situation in which deaf people cannot get any visual cues by reading lips, notes coauthor Susan G. Fisher of the Hines (Ill.) Veterans Affairs Medical Center. In most cases, recruits with implants could pick up a few words and use that information to supplement their lip-reading skills, she says.

This is the first prospective, randomized trial of cochlear implants, notes Thomas Balkany of the University of Miami (Fla.) School of Medicine. Such trials provide more reliable information than retrospective trials, which study old medical charts to see how hearing ability changed after a patient received an implant, he notes.

Despite the promise offered by cochlear implants, they do not provide people with a complete solution to hearing loss. "Caution in interpreting these findings is prudent in view of the wide range of results among patients:' Balkany writes in an editorial that accompanies the study. "Even when improvement is substantial, patients' ability to hear does not approximate that of normal subjects."

The study doesn't address the social issue raised by cochlear implants, Balkany adds. Some deaf people object to the use of such implants, arguing that deafness is a way of life and not a disability.