It is in a later seminar, in 1954, that Lacan, reflecting on the technics of the mirror dialectic, assigns a "materialist definition" to the phenomenon of consciousness by means of a metaphor of a particular type of photography. This will have entailed a revisiting, however elliptically, of a Cartesian cybernetics, an ego ex machine, playing against Walter Benjamin's 1937 essay "Das Kunstwerk im Zeitalter seiner technischen Reproduzierbarkeit" (it is precisely the camera, as a mechanism of the gaze, by means of which Lacan envisages a certain "aura" as affecting itself, as we shall see, in the peculiar form of a psychoanalytic sublime or sublimates).

In a hypothetical world in which man has disappeared, there remains only this mechanical form of reflexivity: a camera alone in nature. The "presence" of this camera is made to "mirror," in a sense, the non-presence of man. At the same time, an actual mirror, although we are not told this (we expect it), is itself "in" the camera, while the camera itself is trained on the surface of a lake, in which there appears an inverted image of a mountain. And despite, as Lacan says, "all living beings having disappeared, the camera can nonetheless record the image of the mountain in the lake," which is thus also (paradoxically) a record of its non-presence there. But Lacan goes further and ponders a certain incendiary intervention:

We can take things further. If the machine were more complicated, a photo-cell focused on the image in the lake could cause an explosion to take place somehow -- it is always necessary, for something to seem efficacious, for an explosion to take place somewhere -- and another machine could recall the echo or collect the energy of this explosion. ("A Materialist Definition of Consciousness," Seminar II, 47)

But there is a slightly different way of looking at this: supposing that in place of this oppositional arrangement of the organic and inorganic (physis/techne), with its Rousseauesque overtones, there were merely the camera positioned in front of a mirror. Assume, then, that something or other sets in train the course of events described by Lacan above: photo-cell, explosion, echo, an "other" machine. What is left in the mirror? in the illusory depth beyond the glissant surface of the lac? Perhaps, after all, it will be nothing but an illuminated blind, a trail of light, in which the image of the explosion in fact ruins the visible. And whether or not this is recorded by some third party, it will have been nothing other than the "consciousness" of an impossible event, in which the ego has still not managed to resurrect itself.

Of what is left in this double mirror, kept or retained there, the trace of a circuit of symbolic capture or détournement. (The illusionism of a mirror which both reflects and transmits.) A mechanism or aperture effect: written on the sensitised film (memory screen), which is immediately exposed, "erased" the moment the film loses its transparency, becomes opaque in the light. Explosion, after effect of the image burnt into the mechanised retina. (The incendiary counterpart of that other mystic writing pad?) But as Lacan says, "the symbolic world is the world of the machine." Hence it is a matter of having confused the symbolic relation as being some thing -- some thing which thinks -- beyond the surface appearance, or disappearance, of the mechanics of reflexivity.

This "mechanism" is not identical to the auto-mobile, god-like phantom of metaphysics described by Pythagoras (anima est numero se ipsum movens, "the spirit is the number that moves itself") and Aristotle (who in De Anima argues that the soul, as seat of consciousness, is the principle of all movement, or prime mover). Consciousness, rather, "is linked to something entirely contingent, just as contingent as the surface of a lake in an uninhabited world." Moreover, for "consciousness to occur each time" there needs to be a surface on which it "can produce what is called an image" -- whose form and operations it would simply "mimic" through a type of mirror-play or counter-surveillance. But this production does not describe an affirmation of the "subject" in itself or even of what is called an image: it is a symbolic play of production, and insofar as he is committed to a play of symbols, "man is a decentred subject." ("A Materialist Definition," 47; 49.)