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computer displays and interfaces function as control mechanisms that maintain the equivalence of communication. For this reason, control—conscious or unconscious—is among the most relevant research tasks in the area of interactive systems.
Today’s systems convey to the user impressions or sensations that are only partially attributable to his own sensory or motor activities, since the possibilities of interaction and the generation of outputs (for instance, moving three-dimensional images, or sound) are determined by the particular program constituting the user’s field of action. In the measure to which the user cannot completely control the cognitive processes of interactive communication in the simulated environment, part of the control must necessarily be exercised by the system itself.
The actions of the observer thus exercise a fundamental and complementary function in interactive systems. The resultant need for synchronous humanmachine reactions, and the interdependence between the context of the subject and that of the system
environment, lead to the question of the different typologies of interactive systems and their strategies.
Various works of media art deploying reactive systems and digital images at the same time directly or indirectly investigate the changes that the observer, by means of data manipulation over interfaces, can bring about in the work. Three models of interactive system can be roughly distinguished on the basis of media-assisted forms of interactivity: 
— Discrete or active systems: although the user can control the content called up, and the sequence in which this occurs, he/she has no influence on the transmitted information, since the management of this information, which demonstrates predictable behavior, is integrated.
— Reactive systems: the work’s behavior, which is media-assisted and based on feedback structures, results from the direct reaction to external stimuli, for instance user control or altered environmental conditions. Selection methods and recursive events create cognitive situations for the participative user.
— Interactive systems: open program structuring,