Friday, October 25, 2013

People who have cochlear implants placed in their heads had often
never heard a sound in their lives before their implant. Once the device
is placed, they can experience hearing, and often can even understand
human speech. Hearing music, however, has remained out of reach.

But now, researchers at the University of Washington in Seattle have
developed an algorithm that vastly improves the sound quality of
existing implants to the point where music sounds like something other
than a random clamor.

People with the current versions of cochlear implants can hear
rhythm, said Les Atlas, a professor of electrical engineering. Atlas
himself has a partial loss of hearing. Subjects whose implants have been
given a "major tweak" with the new algorithm can tell the difference
between instruments.

"If they are hearing a single guitar, they can hear one note," said
Atlas of current wearers. "If a person is playing fast, they can hear
that. If a person is playing slow they can hear that."

However, the new algorithm does not allow their hearers to discern melody; that's the next project.

Cochlear implants relay sound from a microphone placed outside the
ear to a device connected to the auditory nerves inside the ear. The
sound a cochlear implant conveys is just a fraction of the sound a
person with normal hearing can detect. But, for people with damaged
sensory cells, they are the only hope of hearing much of anything.

The Washington study deliberately set out to modify existing devices
so that people would not have to buy new implants to hear music.

The new algorithm was tested on eight cochlear-implant patients, and
the researchers used anecdotal reports and computer simulations to
recreate what the subjects heard.

Atlas said what implant patients hear now is the equivalent of
someone playing a piano with their forearms. All the sound is "mushed
together," and it is impossible to pick out a tune. Or, they can hear
someone singing but cannot tell the difference between a man or a woman,
a baritone or a soprano.

Music is characterized by attributes such as pitch and timbre. Pitch
defines the melody notes of a song and the intonation of speech. Timbre
is the difference in sound between instruments. For example, an A
natural played on an oboe sounds different from a trumpet playing
exactly the same note.

It is the pitch and timbre Atlas and Rubinstein were trying to
improve. With the new algorithm, they could expand what most -- not all
-- of the subjects heard from one octave to three. A low note could have
a frequency of 80 cycles a second, or Hertz, something users of
conventional implants can hear. With the new algorithm, some could hear
up to 320 Hertz, closest in pitch to the E above middle C on a piano.

There is still a vast amount of aural information the new algorithm
misses. Subjects can hear individual instruments, but a symphony
orchestra is a cacophony.

The work is important because music is the hardest thing to hear,
explained Charles Limb, a professor of otolaryngology, head and neck
surgery at the Johns Hopkins Medical Institutions in Baltimore, a
faculty member of the Peabody School of Music and science advisor to the
Baltimore Symphony Orchestra. He said the Atlas-Rubinstein work is
well-known in the cochlear-implant community.
Speech is relatively easy, Limb said, because the purpose of speech
is to communicate a thought, which does not depend on high-quality
sound. For example, the voice of Siri on Apple's iPhone communicates
information effectively despite the artificial nature of the sound
itself.

Music, however, depends on the quality of sound, he said.

Cochlear implants are getting better, he said, but getting better at speech. Little research has gone into music.

"Music is the hardest thing you can hear," he said. "If you can hear
music, you can hear anything. If you design the perfect cochlear implant
that could hear something like music very well then you can hear
anything there is in the world."

Joel Shurkin is a freelance writer based in Baltimore. He is
the author of nine books on science and the history of science, and has
taught science journalism at Stanford University, UC Santa Cruz and the
University of Alaska Fairbanks. He tweets at@shurkin.