FOR speakers of Mandarin Chinese, being unable to detect variations in the
tone of spoken words can be embarrassing. The word 鈥渕a鈥� may mean 鈥渕other鈥�,
鈥渉orse鈥� or 鈥渢o scold鈥�, 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 鈥渉ello!鈥� you use to greet a friend is quite different from
the tentative 鈥渉ello?鈥� 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鈥檚 department of phonetics and linguistics have found a way to simplify a
language鈥檚 tonal information so it can be more easily picked out by deaf
people.
Advertisement
鈥淲e accept the fact that deaf people have limited abilities,鈥� says Rosen. 鈥淪o
we鈥檙e pulling out those parts of speech that they can鈥檛 get any other way.鈥�
The prototype device, called the 鈥淪iVo鈥� 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.
鈥淚t sounds a bit like listening to someone across the wall in the next
house,鈥� 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鈥檚 colleagues in
China.