Robots Have Senses Too
The LEGO Mindstorms NXT kit can “see" through the use of the light and ultrasonic sensors, though it needs two sensors for the price of our one (our binocular vision allows us to determine range to an object as well as orient ourselves relative to our surroundings - for that matter, our hearing does, as well). The light sensor sees in terms of light intensity, or how bright a light source is, as well as detecting colors on a greyscale; however, its field of vision is extremely limited, as is its resolution. Think of it as viewing the world through a peephole!
Though it is very limited, the sensor enables the NXT to perform such tasks as following a line or seeking a light source. The ultrasonic sensor performs only one function, using sound outside of the range of human hearing in the same fashion as a bat, relying on timing the reflection of that sound bouncing off objects to determine their range.
The NXT can “hear" after a fashion, but it is incapable of discerning patterns or frequencies in the noise it hears. It is restricted to being able to determine the amplitude or volume of that sound. (While many people have heard the term decibel, or dB, most don’t realize that it is measured on a logarithmic scale, just like a more commonly cited example, the Richter scale.) For those interested in discussing the science of robots with their kids, both the sound and light sensors measure the intensity of a given parameter at a specific distance from the source, and both are governed by an inverse square relationship (doubling the distance reduces the amount of energy received by a factor of four, and so on).
We rely extensively on our sense of touch when interacting with objects; our skins can convey presence, texture, and warmth. Our robot is not quite so sophisticated, since its touch sensor is a simple on-off affair. Still, this sensor can be a very useful way to trigger simple reactions.
An often overlooked sensor in the NXT is the rotation sensor included in each motor; it may not seem like a big deal, but it allows the motors to mimic your own ability to “feel" the position of your limbs (even with your eyes closed!) and move them at different speeds when necessary.