When we make reference to ``CHI'' (Computer Human Interaction) we call attention to the boundary between humans and computers --- CHI becomes a self-fulfilling prophecy, emphasizing this boundary. A goal of `existential computing' is to eliminate this artificial (unnecessary) boundary by ``becoming'' the computer, rather than merely interfacing to it.
An example of an existential user interface is the author's `finger mouse' (based on `WearCam' as in input device). (See Fig 1),
Figure 1: `FingerMouse': (a) Early prototype of author's `existential computer' invention with camera. (b) Back view of author and apparatus together with object being outlined (luxo lamp). (c) What wearer sees through the glasses: outline of the object that denotes path of moving finger around in the space between the camera (taking the role of eye) and the object. Image is frozen for near-perfect registration. (Thanks to Thad Starner and Flavia Sparacino for help in getting XFakeEvents to work for this).