Canterbury scientists teaching the blind to ‘see’ through their ears

Press, 2 August 1977, Page 17

Canterbury scientists teaching the blind to ‘see’ through their ears

By

ERIC BEARDSLEY,

Information Officer,

University of Canterbury

Bats, as blind as — well — bats, flit easily about their dark world, guiding themselves by hearing the ultrasonic sounds they emit bounce back from obstructions in their path. Professor Leslie Kay has adapted this animal sonar in a range of devices he and his team have developed in the Electrical Engineering Department which he heads at the University of Canterbury: sonic “spectacles” for the blind, which have been developed commercially; a similar aid for blind babies; a device for locating schools of fish in the sea; and a pocket-size instrument called a cardiophone to assist general practitioners in the diagnosis of heart disease and in monitoring the heart of a foetus. All the devices are relatively simple in concept.

Just as bats use echoes, the devices emit a wide beam of ultrasound and then receive echoes from objects in the beam. The echoes are converted to audible form for the brain to analyse. The proximity, size, and texture of the objects which have been coded into the audible sound form an "acoustic” image for the user. A blind per, son using the sonic spectacles is thus able to “see” with sound. A doctor can perceive the real motion of parts of the heart which he can recognise from their position and sound patterns. Experience with the sonic spectacles, which are now manufactured in Christchurch, revealed the remarkable ability of the human auditory system to process entirely unfamiliar and complex sounds. Blind users have found they can distinguish between trees with and without leaves at distances of several feet, and some can even tell the difference between trees with different leaves. The rich sound patterns carry spatial information which the brain appears to handle with relative ease once the basic concepts have been grasped. Professor Kay says. But, with blind babies, there were problems not faced by adult users. In a sighted baby the develop-

ment of sensory motor skills depends largely on hand-eye co-ordination — it can see both its hand and the object for which it is reaching. If that visual link is replaced by a sonic link, the baby needs to sense both its reaching hand and the object. This was not possible with the first sonic aid. The object could be sensed, but not the reaching hand. The answer developed by Professor Kay and his team, which includes a psychologist, was to change the design to arrange for both the reaching hand and the object to be sensed as quite separate things. In fact, the team developed a “family” of four aids for the blind, each with its own special application. One was a single subject sensor, an easy-to-learn aid for adults, after which they

could graduate to a shortrange frequency modulated monaural aid for indoor use. The third is a longrange binaural (stereo) aid for adult use out of doors; and there is a short-range binaural aid for blind children. Professor Kay says the short-range aid has several advantages for children in the confined and often cluttered spaces found indoors. Aids with larger sensing ranges detected targets which an infant, being unable to walk, would be unable to touch and thus learn to appreciate. Most objects the child could sense with the- shortrange aid would be within reach and the child could more easily teach himself by correlating touch and sounds. As the child grew up and began to crawl about, the range code could easily be changed to increase the sensing distance. A totally blind boy, aged two years and a half, has been trained to use an aid. After only three short training sessions, he was able to reach out for a cup jof milk sensed through the aid. The boy, who was unable to crawl at that stage, is now walking about wearing the aid. It was the ability of blind users to discriminate between moving objects that led Professor Kay to consider the possibility of

using a modified sonar system to assist in the diagnosis of heart disease. When diagnosing disorders of the heart, cardiologists mainly want to study movement, both displacement and velocity, and an instrument only as big as a pocket calculator has been designed to complement the use of the stethoscope. It provides similar information to that from the much more expensive echocardiograph machine. In laboratory and preliminary clinical trials, the cardiophone has performed well. Using the instrument, Professor Kay says, it has been found relatively easy to locate and listen to the positional change of the four valves in the heart. It is simple to distinguish between the sound patterns produced by the motions of a normal mitral valve and those produced by the

motion of a severely stenotic, or strictured, valve. The cardiophone supplements information that can be obtained in other ways — in other words it is confirmatory rather than diagnostic. But, says Professor Kay, it could have a valuable role. “It is small, portable, and relatively inexpensive, and could be a useful adjunct

to the stethoscope in the general practitioner’s office. Certain valve disorders may be easily detected and, with practice, it should be possible to make more precise discriminations about the severity of the disease. “The signal can be easily recorded on a standard audio cassette so that the records obtained during the course of a general examination over a period of years can be compared to reveal gradual changes in the patient’s condition. In addition a visual record may be produced by using a special spectrum analyser.” He says that if the ability to recognise patterns of motion with the cardiophone leads to improved diagnosis at the general practitioner level, and aids the cardiologist in monitoring patient progress, it is both complementary to the stethoscope and electrocardiograph machines used by the genera] practitioner. There is no other comparable instrument. The third application of the sonar principle is an aid in the location of fish. Professor Kay believes this has considerable potential as an effective aid to the growing New Zealand fishing industry, particularly for pelagic fishermen engaged in purse-seine fishing. He has used it successfully to locate underwater objects in Lake Coleridge and schools of fish off the

Poor Knights Islands, in Northland, and he believes extensive trials in a fishing boat are now justified. Most sonic devices to locate shoals of fish use pulse systems, with a narrow beam searching ahead of the ship and a visual display which may show the shape of the shoal within the beam. Professor Kay designed such systems in the 19505. They are costly and few are in commercial use. But, says Professor Kay, if the sonar is designed for an auditory display, using both ears in a natural binaural mode — as had to be done to provide an effective aid for the blind — an entirely new medium for locating fish is available. “The needs of fishermen are very similar to those of the blind,” he says. “Both wish to view their immediate environment, up to six metres for a blind person and perhaps 1000 metres for fishermen. An acceptable field of view may be 60 degrees. Within this viewed volume the fisherman wants to locate and recognise shoals of fish and catch them in the most cost effective way.” In both the blind aids and the fishing sonar, the distance to a reflecting object is determined by the pitch of the echo note. There is no need con-' sciously to determine the distance with high accuracy.