The below quotes are from sections about true perception and how it works while still in a body.
It speaks of how the body's eyes STILL see what seems to be an "outside world" of differences, forms, bodies, places.
However, the mind is responsible for INTERPRETING, the messages which come in FROM the body's eyes. The body's eyes can ONLY look upon the physical world of form and never has real vision. The body's eyes cannot look past the world of forms and differences. So it is up to the mind to determine whether the "signals" coming to it are TRUE, or FALSE.
ONLY THE MIND PERCEIVES, not the eyes! Perception is not about what the body's eyes see AT ALL. The body's eyes just collect "data" and send it to the mind to evaluate. The body's eyes cannot ADJUST to anything. They cannot "see differently". They cannot change perception.
They can ONLY LOOK AT the world you made as hell. The physical form of the Earth. They cannot and do not INTERPRET what they see, because they were made to FIXATE ON FORM. They are neutral. They do not "see lovingly" nor do they "see hatefully" or fearfully.
A healed mind will put all such signals into a category of "false", *recognizing* that *everything* the body's eyes "see" is an ILLUSION. It recognizes they are ALL UNREAL.
The body's eyes at this point are still "seeing" the forms of the physical world. But the MIND, which is responsible for SEEING, is now seeing with forgiveness and recognizing that the physical world is ENTIRELY illusion. That every signal coming from the body is FALSE, and therefore totally unreal.
This is why in TRUE PERCEPTION, you STILL SEE the world, the bodies, the world events, all the same as before, but your MIND interprets the whole thing as FALSE, because it sees with the whole truth.
As stated below, reality is without size, shape, time or place and differences DO NOT exist in it. Heaven has no forms. And so in comparison to this, a mind aware of the truth knows that all forms, shapes, times and places are NOT reality. And so such a a mind perceives that the physical world of forms is NOT REAL.
Note it is also clear here that PERCEPTION is not about what the BODY'S EYES SEE, it is a function of the mind which either mistakenly interprets those "visual" signals and thinks that some of it is real, or correctly interprets those signals entirely as unreal. This is why you must not "believe your eyes" at all.
"M-8.3. Where do all these differences come from? 2 Certainly they seem to be in the world outside. 3 Yet it is surely the mind that judges what the eyes behold. 4 It is the mind that interprets the eyes' messages and gives them "meaning." 5 And this meaning does not exist in the world outside at all.
What is seen as "reality" is simply what the mind prefers. 7 Its hierarchy of values is projected outward, and it sends the body's eyes to find it. 8 The body's eyes will never see except through differences. 9 Yet it is not the messages they bring on which perception rests. 10 Only the mind evaluates their messages, and so only the mind is responsible for seeing. 11 It alone decides whether what is seen is real or illusory, desirable or undesirable, pleasurable or painful."
"M-8.6. The body's eyes will continue to see differences. 2 But the mind that has let itself be healed will no longer acknowledge them. 3 There will be those who seem to be "sicker" than others, and the body's eyes will report their changed appearances as before. 4 But the healed mind will put them all in one category; they are unreal. 5 This is the gift of its Teacher; the understanding that only two categories are meaningful in sorting out the messages the mind receives from what appears to be the outside world. 6 And of these two, but one is real. 7 Just as reality is wholly real, apart from size and shape and time and place—for differences cannot exist within it—so too are illusions without distinctions. 8 The one answer to sickness of any kind is healing. 9 The one answer to all illusions is truth."
Notice also that in terms of "projection makes perception", the quotes above state that the mind projects its hierarchy of values and preferences outward, THEN it sends the body's eyes to try to "see" that, the body now looks only at the FORM of the physical world, sends back signals of its physical nature, the mind is now FILTERING that signal through its belief system of values/hierarchy/preference, and only SELECTS what it wants to allow into awareness. This is described here:
"What perception sees and hears appears to be real because it permits into awareness only what conforms to the wishes of the perceiver. This leads to a world of illusions, a world which needs constant defense precisely because it is not real....When you have been caught in the world of perception you are caught in a dream."
Remember that perception is a function of the MIND, not the eyes. So here, the mind is filtering through its perception, its interpretation of body signals, what it wants the signals to mean. It only allows into awareness, the root of the perceptual system, that which makes it through the filter.
Therefore if the mind has false perception ie false interpretation and projections of filtering beliefs in attack etc, it is now MIS-perceiving and hallucinating a distorted version of the visual signals it's getting from the eyes, and READING INTO them, and EXCLUDING what it does not want to look at, in order to make it SEEM as though it's seeing the reality it PREFERS. "Perception SELECTS and makes the world you see." But the "world you see" is happening in your MIND, in your perceptual interpretation function, regardless of the world that is "out there".
Here is some additional material:
"Reason will tell you that the form of error is not what makes it a mistake. 2 If what the form conceals is a mistake, the form cannot prevent correction. 3 The body's eyes see only form. 4 They cannot see beyond what they were made to see. 5 And they were made to look on error and not see past it. 6 Theirs is indeed a strange perception, for they can see only illusions, unable to look beyond the granite block of sin, and stopping at the outside form of nothing. 7 To this distorted form of vision the outside of everything, the wall that stands between you and the truth, is wholly true. 8 Yet how can sight that stops at nothingness, as if it were a solid wall, see truly? 9 It is held back by form, having been made to guarantee that nothing else but form will be perceived."
"These eyes, made not to see, will never see. 2 For the idea they represent left not its maker, and it is their maker that sees through them. 3 What was its maker's goal but not to see? 4 For this the body's eyes are perfect means, but not for seeing. 5 See how the body's eyes rest on externals and cannot go beyond. 6 Watch how they stop at nothingness, unable to go beyond the form to meaning. 7 Nothing so blinding as perception of form. 8 For sight of form means understanding has been obscured."
"Only mistakes have different forms, and so they can deceive. 2 You can change form because it is not true. 3 It could not be reality because it can be changed. 4 Reason will tell you that if form is not reality it must be an illusion, and is not there to see. 5 And if you see it you must be mistaken, for you are seeing what can not be real as if it were. 6 What cannot see beyond what is not there must be distorted perception, and must perceive illusions as the truth. 7 Could it, then, recognize the truth?"