First off, god damn, this thread moves fast.
Second:
Mind comes from the brain. It IS describing physical interactions within the brain.
The brain is complex, and does many things that are very distant from any direct external influence. According to the theory that there is no mind beyond the brain's function qualia are just the result of complex interpretations of external stimuli. Red is a definable trait of physical objects. The 'absolute' red may differ slightly between individuals, but the existence of red as a concept held by the community re-enforces that red be considered a distinct colour as opposed to pink or maroon or something. People have language, whose source I do not want to debate, but which requires the defining of specific elements. So red exists because language describes the colour of objects, the only remaining question is: Does red have any significance beyond a physical property?
That's where the confusion between us is coming from, I bet. The quale "redness" is abstract, non-physical and ineffable. There is a big difference between saying, "This person's neurons are firing in a way consistant with a person seeing light with a wavelength of approximately 650 nm being reflected off of an apple." and saying "This person is experiencing a sensation of redness in that apple."
Imagine for a moment, a physical system identical to a living person's body except without any ability to sense quale. If we assume materialism is correct, (pretty good assumption to make) than that system would behave exactly like a living person. It would eat, breathe, move around, and even think. It would be alive in every measurable way and effectively the same as a normal person. The only difference is that it doesn't experience anything except in the physical sense of memories being assembled by neurons firing in a way that results in the portions of the brain that store memory arranging themselves to store memory.
While we can explain behavior and sensation with chemistry and physics, we can't explain why we are aware of the universe when, as far as I can tell, it's utterly indisguishable from one with pure mechanical determination and without any non-physical sensations or awareness.
Well two things...
1) We don't know exactly when sentience and sapience comes about. We do know that it has to be a natural process as other animals in other environments have some levels of it. Though to not our obese end.
2) Unexplained != Magic.
We must stride to never simply invent an answer to fill a void of information. These false assumptions offer little if anything of merit at all. Its just bad form. There nothing wrong with going. "I don't know."
As for your person that doesn't have perceptions of anything. I would argue that he would be alive in the since, that he eats and poos. But he wouldn't be alive in the since of living. Enjoyment, reacting making contributions.
The none perception person would be incapable of thinking. Thinking is a byproduct of sensory input. Imagination is probably the byproduct of spare cycles. Its not as fluffy bunny super extra special, but it doesn't need to be. Human are amazing in many amazing details that its silly to invent them.
Our mind is active because of sensory information. And our mind makes up reactions when deprived of sensory information. This is the hallucinations experience in sensory deprivation environments or when a sensory organ is impaired slightly. The tell tale seeing things out of the corner of your eye in a dark room.
We can also look at it from another angle. That if there is no sensory information then why would the brian think? The automated process happen in the background absent of our knowledge or forethought so that really thinking. Majority of our brian would simply be resource hungry vicegeral organ.
The none sensory person wouldn't even dream.
I cannot see this none sensory person being alive in any meaningful matter. Yes, these means that comatose patience aren't alive either. [I have a living will with parameters about that.]