Keep talking

the easiest mode of communication, talking, and the one that we have always taken for granted, can prove to be difficult for many people. Those who have difficulties with speech are learning to pronounce words more clearly using an artificial palate that "tells' them exactly what their tongue is doing.

Many deaf people find it hard to speak clearly because they cannot hear what they are saying, while people with cleft palates have speech problems because of the unusual structure of their mouths. Now, a computerised instrument called the electropalatograph can help both groups overcome their respective speech difficulties.

The electropalatograph relies on an artificial palate studded with 62 small electrodes, each one 1.2 millimetres in diameter. Each palate is individually tailored to fit a particular person using a cast taken from the roof of his/her mouth. "It's a bit like a denture without the teeth,' says Bill Hardcastle, head of the department of speech and language sciences at Edinburgh's Queen Margaret College, uk , and one of the developers of the device.

The sensors are arranged in eight rows, with eight electrodes in each row excluding the first, which has only six as the mouth is narrower towards the front teeth. When the tongue touches an electrode, it completes a circuit and a very low current flows. Hardcastle says it is relatively easy for a computer to screen out false signals caused by the saliva completing the circuits, as saliva does not form a good contact as the tongue.

The grid of electrodes records the position of the tongue over 100 times a second. This information is then passed on to a computer which displays it on a series of grids that match the arrangement of the electrodes.

By watching what their tongue is doing and comparing it with the standard tongue movements, people with speech impediments can learn how to "shape' different sounds. When the tongue touches roots of the front teeth, for instance, it helps form t, d and s sounds. Pronouncing a j involves touching the hard palate towards the middle of the roof of the mouth, while k and g sounds are produced when the tongue touches the soft palate at the back of the mouth, called the velar.

Hardcastle claims that the artificial palate can help those who have gone as far as they can with conventional speech therapy. "It gives them an extra insight,' he says. The main deterrent of the electropalatograph, even if a portable version of the machine is launched, will be its cost. At the projected prices, it will remain beyond the reaches of those who need it the most. Right now, researchers are busy devising ways to manufacture the machines more cheaply.