GIVING visually impaired people a virtual doppelg盲nger with the ultrasound abilities of bats could allow them to better navigate their surroundings.
Sounds such as beeps are sometimes emitted at safety-critical locations such as fire exits or pedestrian crossings to help visually impaired people find their way around. Bat-like echolocation would enable them to sense a whole lot more of their environment via hearing.
Bats locate obstacles by producing rapid streams of ultrasonic clicks. They use the time delay and volume of the echoes to determine how far they are from the objects that reflected them. The bat鈥檚 use of ultrasound is key: ultrasonic waves diffract, or spread around obstacles, much less than audible frequencies, allowing the bat to perceive the objects around it clearly.
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Ultrasound is too high-pitched for us to hear, though. Even if we could, sound echoes come back too fast for us to make sense of the delays. Now Dean Waters at the University of Leeds in the UK has worked out a way around these limitations. Instead of trying to make ultrasound work in the real world, he makes it work in a virtual one. Then he translates the data into frequencies people can hear.
Each area to be navigated 鈥� a building, say 鈥� has to be re-created as a 3D computer model. Then a visually impaired user wears a sensor that tracks their position and motion as they explore the real-world environment. Data from the sensor directs a virtual representative, or avatar, in the virtual environment to reproduce the user鈥檚 movements. The avatar emits virtual ultrasound that bounces off the virtual surfaces of the environment to produce virtual echoes, which are then converted into audible clicks that the real-world user hears in headphones. The stream of clicks changes as the user approaches an obstacle, so the system will enable them, with practice, to navigate the environment. In principle, the same system could allow visually impaired people to navigate virtual worlds such as Second Life.
Waters and his colleague Husam Abulula created a virtual model of a local mosque and placed in it a moth that did not exist in the real mosque. They then asked volunteers equipped with motion sensors and headphones to explore the real building. The participants could hear both the outgoing click stream and incoming echoes and learned to use them to find the moth. Eventually, the average length of the routes they took were only twice as long as the most direct route, according to a forthcoming issue of the International Journal of Human-Computer Studies ().
But Mikael Fernstr枚m, an aural display specialist at the University of Limerick, Ireland, doubts the idea will prove popular. 鈥淭he last thing visually disabled people want to do is put earplugs in their ears. They want to experience the world immediately, as it is,鈥� he says.
