But it didn't happen. For one thing, it's not easy to learn concepts like math and science by listening to a droning computer voice; students still need some sort of tactile interaction. Not everyone wants to passively listen, but Braille is the only way for blind people to read. Several types of electronic Braille devices are available, but they're often prohibitively expensive -- desktop devices range from $6,000 to $10,000 per unit, and portable devices, which are limited to one line of text at a time, can cost $3,500. The result has been a staggering drop in Braille literacy -- today, about 10 percent of blind people can read Braille, about one-fifth the amount that could read it 40 years ago.