By Elizabeth Cloutman

Photo by Monique Schoenfeld, Town Crier

Hearing breakthrough

Last week, Bernard Widrow, an electrical engineering professor at Stanford University, altered the life of a 46-year-old Palo Alto man, who has been profoundly hearing-impaired since birth.

The man’s father had invited Widrow, a colleague at the university, to his home to demonstrate the microphone array necklace on his son. The device is an invention by Widrow and two graduate students, Jim Lehr and Steve Mims, to assist people with severe and profound hearing loss in discerning speech.

“This fellow … said that not in 46 years had he heard that well,” Widrow said. Previously, even with two hearing aids, the man had been able to comprehend conversation with his father only by using his excellent lip-reading skills, even sitting at close range in a quiet room. With the microphone array device, he could close his eyes and understand everything his father said, Widrow said.

“This is not the first time I’d seen it. It’s the umpteenth time, but you still get joy out of that,” Widrow said of the experience. Since hearing loss is highly variable among individuals, not everyone will have the same results as his colleague’s son, Widrow said; but clinical trials over the last seven years have shown that for many, the microphone array necklace can make a difference in their lives.

The hearing array necklace, also known as a directional hearing array, is not a simple amplification device like a hearing aid, but rather is used in conjunction with a hearing aid to boost conversational sound while muting extraneous noise. The hearing array uses many of the techniques of adaptive signal processing and neural networks that Widrow has spent his entire career developing. Adaptive signal processing employs the “least mean square” algorithm that Widrow and Los Altos resident Ted Hoff developed in 1959 to reduce the noise in an electronic signal. Neural networks are engineering systems that can, like the brain’s neurons, learn from experience. Neural networks’ applications include speech and pattern recognition and control systems. (Widrow is also the inventor of the adaptive filter, which enables computer modems to work at speeds that make the World Wide Web possible.)

The six microphones mounted on the hearing array necklace beam in the sound waves entering a 60-degree-wide, cone-shaped space in front of the user. The microphones transmit the sound to signal-processing chips that assign different weights to the input from the various microphones. As a result, the microphone array is able to hone in on the desired signal and reduce unwanted echoes and other auditory effects while increasing the clarity of the dominant signal. The optimized signal is amplified and sent through a conducting neck loop - the reason for the necklace design - as a magnetic signal. The magnetic signal is transmitted wirelessly to a telecoil in the user’s hearing aid, which converts it back to an auditory signal. (Hearing aids commonly feature the telecoil to facilitate a hearing-impaired person’s use of the telephone.) The necklace also contains an on-off switch and volume controls that permit the device to be adjusted to individual needs.

Widrow explained why the microphone array necklace enables the severely or profoundly hearing-impaired person to better comprehend speech. “(Even in a quiet room,) the problem is the sound traveling between the person speaking and the hearing-impaired listener goes by many pathways from the source to the receiver,” Widrow said. “The sound bounces from the walls, the ceiling and the furniture. There are basically an infinite number of pathways. … It’s called reverberation. so the person hears the sound over and over again at different amplitudes. “People with normal hearing are accustomed to the reverberation, he said, but for the hearing-impaired, it greatly reduces speech clarity. A noisy environment, such as a restaurant or party, makes it extremely difficult for a hearing-impaired person to converse as hearing aids amplify background noise as well as conversation, he said.

The hearing array necklace allows only those sounds coming in at horizontal and vertical 60-degree angles in front of the hearing-impaired person to be amplified and transmitted to the hearing aid telecoil, Widrow explained. Therefore the device enables the hearing-impaired, who orients his or her body to face the person he’s conversing with, to comprehend conversation in a way not previously technically possible.

Starkey Laboratories, a Minnesota-based company, has agreed to manufacture the hearing array necklace, which took over a decade to develop and test, if Widrow can find someone to market it. In the meantime, just as a result of a June press release, Widrow said he has received a large number of e-mails from those wanting to try the device.

“If people in the Los Altos area who are (severely or profoundly hearing impaired) would like to try it, that would be possible … (although) I hesitate in some sense to do it because I could get deluged,” Widrow said. “The number of people who have (come) just out of Stanford is surprisingly large. They just cannot get what they need out of a hearing aid.”

Widrow may be contacted by e-mail at widrow@stanford.edu.