Interactivity - what is it? In describing interactivity as a creative mode that offers an important toolset for contemporary artists, it is helpful to start with a comparison to another time-based technological art-form, that of traditional animation art.
In contrast to traditional animation, contemporary techniques of Interactive Art use the construction or customization of software and/or physical components, to emphasize the interactive partnership of the artwork with the audience itself - the audience "completes" the work. This is a familiar idea to those who pay attention to the structure and dynamics of computer games. The audience enters into the artwork as the human component of a Dynamic System, a Sensorium assembled by the artist. This Dynamic System (or set of interacting systems) displays behaviors that the audience can affect, and at the same time this very same audience is affected by the Sensorium in which it is immersed. An example of this is a sound and video environment where an audience's physical movements and locations in the exhibition space can affect both the images displayed and the sounds that surround them. The images and sounds affect the audience (emotionally, aesthetically, physically) and the audience itself can reciprocally affect the visual and sonic environment, changing that environment by moving around in it. Adding environmental as well as online network events can richly complicate this Artwork/Audience dyad. The artist can use physical sensors to correlate intensities of such things as temperature, light, humidity, physical proximities, long-distance earthquake data (among many, many others) to expressively extend the interactive artwork. The artist can use these various "inputs" to enrich the morphing, changeable sensorium of the audience - producing not only video and sound displays but also mechanical/robotic events, or biological events, as in some recent works of "bio-media" art.
Interactive Art is a new area of creative expression where the audience is integral to the artwork - the human component of a complex dynamic system or set of dynamically interacting systems.