The brain can basically simulate the rendering equation in real time (or trick yourself into thinking it is, which is the same thing really.)
I believe that your brain is rendering the reality for your consciousness even when you are awake. There is a lot of filtering and processing between your senses and your consciousness. For instance, your eyes produces a lot of noise which is filtered away. They have a blind spot [1], but your consciousness is not even aware of it! So, what you see when you are awake is not really the noisy distorted vision that your eyes have.
In addition to that low level smoothing and filtering, your subconscious has reconstructed completely the reality for your conscious mind: "This is because our brains consist of two relatively distinct regions. One, the cognitive unconscious, makes informed guesses and delivers them to the second, conscious part, which supports our awareness of what we are seeing while knowing little or nothing of how what we see has been constructed." [2]
"All we’re actually doing is seeing an internal model of the world; we’re not seeing what’s out there, we’re seeing just our internal model of it. And that’s why, when you move your eyes around, all you’re doing is updating that model." [3]
So, when your are dreaming, the subconscious mind is just "rendering" something else than reality for your conscious mind.
I'm being specific, I'm not talking about "rendering", I'm talking about the rendering equation, which is the mathematical formulation of light transport. I agree it's amazing the brain is able to interpret the light coming into my eyes into a perception of reality, but the startling thing about lucid dreams is that it is also apparently able to very convincingly simulate the external behavior of light itself properly as well, without external stimuli. (Which is currently an intractable problem computationally FYI.) For example, when I turn my head in a lucid dream under conscious control, reflections, texture, etc, behave what appear to be normal, in real time. This blows my mind.
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I believe that your brain is rendering the reality for your consciousness even when you are awake. There is a lot of filtering and processing between your senses and your consciousness. For instance, your eyes produces a lot of noise which is filtered away. They have a blind spot [1], but your consciousness is not even aware of it! So, what you see when you are awake is not really the noisy distorted vision that your eyes have.
In addition to that low level smoothing and filtering, your subconscious has reconstructed completely the reality for your conscious mind: "This is because our brains consist of two relatively distinct regions. One, the cognitive unconscious, makes informed guesses and delivers them to the second, conscious part, which supports our awareness of what we are seeing while knowing little or nothing of how what we see has been constructed." [2]
"All we’re actually doing is seeing an internal model of the world; we’re not seeing what’s out there, we’re seeing just our internal model of it. And that’s why, when you move your eyes around, all you’re doing is updating that model." [3]
So, when your are dreaming, the subconscious mind is just "rendering" something else than reality for your conscious mind.
[1] http://io9.com/5804116/why-every-human-has-a-blind-spot---an...
[2] http://serendip.brynmawr.edu/exchange/node/2604
[3] http://aminotes.tumblr.com/post/7722763662/david-eagleman-on...
I'm being specific, I'm not talking about "rendering", I'm talking about the rendering equation, which is the mathematical formulation of light transport. I agree it's amazing the brain is able to interpret the light coming into my eyes into a perception of reality, but the startling thing about lucid dreams is that it is also apparently able to very convincingly simulate the external behavior of light itself properly as well, without external stimuli. (Which is currently an intractable problem computationally FYI.) For example, when I turn my head in a lucid dream under conscious control, reflections, texture, etc, behave what appear to be normal, in real time. This blows my mind.