Can We Talk? Speech recognition systems have come a long way in the last decade. Systems that let you "type" into a computer with your voice are already available, and some telephone menus use speech recognition systems to let you make your selections verbally. Processing language is complicated, however, thanks to the different accents and cadences people speak with, and the fact that many words and word fragments sound alike. (Think of there, their, and they’re, or how a Southern accent makes wedding sound a lot like waiting.) That’s why–at least for now–speech recognition systems work best when the vocabulary is limited to a few set commands. Having a robot "talk back" is much simpler; voice synthesizers that convert text into speech only need a programmed list of pronunciation rules to speak intelligibly.

Some robots "see" using ultrasonic sound, much the same way bats do. Such robots typically emit 40 kilohertz sound pulses (too high for us humans to hear), then detect the echoes. Measuring the time delay from when the sound pulse goes out to when it returns gives a surprisingly accurate measure of the distance of objects. An advantage of this navigation technique is that it works in the dark.

Touch sensors help otherwise blind robots with navigation: feelers, contact switches, bump sensors. . .all let a robot know when it has made contact with walls or objects. Piezoelectric material is commonly found in touch sensors. Piezoelectric crystals respond to pressure with a small electric voltage. They can detect vibration, impact, and even heat.

Position sensors on robots make it possible to teach robots to do something–like spray-paint a car–by leading them through the motions. Sensors on the robot’s joints save information about the changing series of positions in computer memory. The robot "remembers" this information and repeats the motions exactly.

Sensors for radio signals and electric and magnetic fields are especially useful in robotics. Radio signals let robots communicate with each other at a distance. Robotic lawnmowers use electromagnetic sensors to stay within the bounds of the yard.

Smell and taste in a robots are not yet quite as refined as our own–nor do they usually need to be. Robots sensors can detect specific gases, however, including gases that we can’t smell on our own. One of the most important uses of smelling robots is airports, to detect the fumes from explosives hidden in luggage.