Interactive art is a form of installation-based art that involves the spectator in some way. Some installations achieve this by letting the observer walk in, on, and around them. Works frequently feature computers and sensors to respond to motion, heat, meteorological changes or other types of input their makers programme them to respond to. Most examples of virtual Internet art and electronic art are highly interactive. Sometimes visitors are able to navigate through a hypertext environment; some works accept textual or visual input from outside; sometimes an audience can influence the course of a performance or can even participate in it.