Re: this is Amy
We don't think anything at all when we hear "This is Amy". We simply understand it to mean "The name of the person I am indicating is Amy".
"This is Amy" when Amy is standing close by and is probably part of the conversation.
"That is Amy" when Amy is not close by, you are probably pointing her out in a crowd, or identifying her in a photograph.
When someone says "This is a table", we don't stop and think "Right, hang on, I must work it out. The item being identified is inanimate (a table), therefore "This" must refer to a thing".
When someone says "This is Amy", we don't think "Hmm, how strange. The last time I heard "This is ...", the person was talking about a table. However, Amy clearly isn't a table or any other inanimate object for that matter. She's a person. Therefore "This is" must now be referring to a person".
You seem to think that some kind of computation goes through our heads when we hear our own language. It doesn't. "This is Amy" is how we introduce someone. It's what we hear from birth till death. It holds no confusion or reason for deep thought for us.
I realise that when you hear something in a foreign language, there is an element of "working it out" in your brain before totally understanding it. But that does not apply to your native language. Or perhaps I should say it does not apply to my native language. Perhaps in yours, you have to actually work out the meaning of the words in your head before understanding them.
Remember - correct capitalisation, punctuation and spacing make posts much easier to read.