Chinese whispers
By Alison Motluk
for speakers of Mandarin
Chinese, being unable to detect
variations in the tone of spoken words
can be embarrassing. The word "ma" may
mean "mother", "horse" or "to scold",
depending on the tone invested in the
word. Yet 50 million profoundly deaf
people in China are unable to make these
distinctions, because lip-reading is no
help when it comes to tones. A hearing
aid jointly developed by researchers at
University College London (UCL) and the
Chinese Academy of Sciences may help
restore that ability and prevent deaf
people confusing mothers with horses.
The only equivalent to this effect in
English is the use of inflection. For
instance, the hearty "hello!" you use to
greet a friend is quite different from the
tentative "hello?" you use if you are not
sure whether there is anyone at home. But
in Norwegian and the Yoruba language of
Nigeria, as well as in Mandarin and many
other languages, changes in tone are even
more critical, as they alone are what
distinguishes differences between words
that otherwise sound exactly the same.
Conventional hearing aids cannot help
because they simply amplify sound, and
do not boost tonal differences. Now
Adrian Fourcin, Stewart Rosen and
colleagues at UCL's department of
phonetics and linguistics have found a
way to simplify a language's tonal
information so it can be more easily
picked out by deaf people.
"We accept the fact that deaf people have
limited abilities," says Rosen. "So we're
pulling out those parts of speech that they
can't get any other way."
The prototype device, called the "SiVo"
aid, is a box the size of an unfashionably
large Walkman. Speech sounds picked up
by a microphone are passed through a
specialised computer chip called a digital
signal processor, which can digitise and
manipulate sound in real time. The
researchers have programmed the
processor to extract the crucial acoustic
features they need, mainly pitch, turning
the sounds into a completely synthesised
signal that has the right pitch but a pure
tone. This muffles words but amplifies
the tonal differences between them.
"It sounds a bit like listening to someone
across the wall in the next house," says
Rosen, describing the effect. But when
the tonal hearing aid is combined with
lip-reading it can vastly improve what
people can understand, he says. The SiVo
system is currently being tested by
Rosen's colleagues in China.