I don't believe existence to be entirely dependent upon physical perception.  If that were true, then when I was first conceived, then it was not until I was able to perceive my own existence that I in fact existed.  If God knew Jeremiah before he was formed in the womb, then obviously Jeremiah existed before he had the capacity to perceive his own existence.  And if the bible is not a source for you, then a fetus will suffice.  All of us were at one point the initial conception of an egg and sperm cell.  Meaning our existence began there.  Had we been aborted, we would not be here, we would not exist, because our existence would have been halted. 
So obviously, some type of existence had to have been there. 

But in response to something chris asked, if someone was born without senses.  Once again, just because they couldn't perceive their existence does not mean, in my opinion, that they exist.  Why?  Well, if there is a God, ( which there is, and His purpose of making us with relationship with HIm, is an apologetics spiel I don't feel like going into right now ) and He is all powerful, totally supra natural, then He is capable of anything.  Meaning He could, if He desired, create someone to be born without a perception of their existence, and then heal them so that they could perceive their existence. 
The question is, if they existed before they were healed.  I would say, yes, because we have a spiritual perception.
You can say that spiritual perception is somehow related to a physical feeling.  In feeling God's presence, I relate it to a physical feeling.  I say no, it is a feeling in and of itself, one beyond the natural, one not capable of being described in the natural, because it is SUPER natural.
You can't naturally describe an emotional healing that from that point on is proven through how I behave differently.  I really don't want to go there, but if you don't believe that something beyond your natural perception can happen when you experience God's presence, then I worry if you believe you can ever experiece His presence.
Go to a camp service and mean it if you disagree.
But anyway, every person is God's child, His creation, and so capable of experiencing that. We are spiritual as well as physical beings.
NOw a bit complicated....
For that person to exist, they have to have a spirit. People are not strictly physical.  I don't want to go here either, but the simple mechanical workings of your body components are not what give you life.  God is the life behind it ( the whole.. two cells through sex made YOU )
So that person does have a spirit, as any one else does.  But their physical being isn't aware of anything.  So God heals the physical, so then they can perceive the natural, but the spirit has always been there. 
You say "no" for whatever reason.
So I ask this: If that person died, wouldn't they go to heaven or hell?
No, they weren't really a human being...
Right.....
So there's my argument.