To perceive means to immobilize. To say this is to say that we seize, in the act of perception, something which outruns perception itself.
Spirit borrows from matter the perceptions on which it feeds and restores them to matter in the form of movements which it has stamped with its own freedom.
When we make the cerebral state the beginning of an action, and in no sense the condition of a perception, we place the perceived images of things outside the image of our body, and thus replace perception within the things themselves.
You will obtain a vision of matter that is perhaps fatiguing for your imagination, but pure and stripped of what the requirements of life make you add to it in external perception.