For our purposes in psychoanalysis, the concept of mental representations of objects cannot be defined in terms of a simple sensory perception system. In order to include the useful concepts of unconscious objects and of the superego we must have a more complex but more precise model of the perceptual system and hence also of the ego. It is essential to distinguish clearly between the psychic perceptual system and the physiological sensory apparatus, since the latter does not by itself determine the perceptual experience. Conscious perception can occur only after a physical sensory experience has been worked over in the unconscious; in this respect sensory stimuli from without are equivalent in kind to stimuli arising from within the organism. A conscious perceptual experience is bound by the principle of secondary revision (elaboration) in the waking state as well as in dreams.

To understand the problem of perception, we must suppose that the ego has multiple functions, which must include both simple sensory perception and the internal representation of