of video. Many artists have made use of this technique in their work. Installations and arranged situations emerge that include the viewer in the representative situation. The special relationship of the simultaneity of reality and depiction forms a basis for so-called closed-circuit situations. Such an arrangement refers to a closed situation of representation in which the recording medium (the camera) is linked directly with the medium of representation (for example a monitor). Often an object or a person is simultaneously confronted with his own image. Observers thus experience the synchronicity of their actions with their depiction, as in a mirror, but this time not reversed. They thus no longer find themselves either within a current situation, which they experience as the present, or its time-delayed representation, which has more the character of reminder or documentary, but rather in a media-extended reality. The visitor thus becomes both actor and spectator.

With the use of the closed-circuit technique, situations for perceptive experiences between architectural and media space can be produced, which are then made current by the presence of the

observer. An early and important work in which the visitor is integrated in the installation is «Wipe Cycle» by Frank Gillette and Ira Schneider (1969).

In addition to its role as a mirror, video is also used in its function as an instrument of surveillance. In contrast to the mirror, the video images are dependent on the position of a recording camera, not on the position in relation to the reflected object. This means self-perception is mediated through a camera eye that can change the perspective in an irritating way, as in Peter Weibel's installation «Beobachtung der Beobachtung: Unbestimmtheit» (1973).

Time space body

The effect of technologically mediated self-perception through a camera is particularly powerful in spatial situations that include the observer. For example, Bruce Nauman produces in «Live-Taped Video Corridor» (1969–1970) irritations of the experience of space and time caused by the feeling of physical presence or absence. Nauman specifically emphasizes in his arrangement the aspect of dependence of physical