This is the area that most robiticists work in. They design a robot, then program it to move according to certain inputs. These robots very widely in shape, purpose, and programming. These sensors are sometimes heat sensors, motion detectors, radar, and many other things. That is one of the things that is hardest to achieve in a robot.
Association is something that humans are incredibly good at, and computers are incredibly bad at.
Computers and robots have to compare something they see with a list of things it could be and to them they either are or are not the same. A robot would also have a hard time treating a lower-case, capital, and cursive letter as if they were the same. Think about all the different fonts you see on TV and the internet every day. A robot would have a hard time reading all of those because they are so different. Just face it.