This robot possesses a sonic tracking system and is fortified with a multitude of sensors: photo transistor to detect a black line, tracking memory to memorize its last track of the black line, and two red LEDs that flash to tell you which side of the light sensor is activated.  By using an infrared emitter, light sensor circuitry and tracking memory, it demonstrates how robots see a pathway.  Make a path with a black felt marker or black tape and watch how infrared sensors enable the robot's motors to make course corrections.