Taking contemporary and early video installations for examples, this paper extends "medium" as the whole bodies of an artwork, that is, the relations between the works, artists, viewers, and the exhibition mechanism. It is completed through rethinking Michael Fried's "theatricality" which denotes some kind of ambiguity viewers experience while facing Minimal Art, and then referring to Merleau-Ponty's dynamic "figure-ground", "narcissism", "Simulacra," with Roland Barthes' "punctum," and finally discriminating Rosalind Krauss, narcissism and reflexiveness. Since the current trend is towards where viewers become inevitable and high technology is turned into art, I try to develop a phenomenology of fields of Installation Art which is an approach directly related to perception of the whole work, different from analyzing artists, styles or power structures. It can be concluded that what Merleau-Ponty called a fundamental narcissism of all vision and what Barthes called punctums are actually dehiscence where viewers enters the works with their own bodies and points of view. Hence they are not passively involved to watch or issue simple commands while the autonomy of art is insisted. And this is how viewers deeply participate or what true interaction is in arts.