Whose voice is that...?

Everyone hears a voice(es) in their head.  Not in the mentally unstable way!!!  In the as you are reading something way.  Whose voice is it???  It isn't my own.  When a book has "British" male characters...whose voice am I using when I am reading...

I have a feeling it is mostly influenced by what we see on TV/hear on the radio.  But what determines whose voice your brain uses.  For example I can't read the last name Miller without hearing a strong Scottish accent.  I know why, I watch Broadchurch...but her last name was also Miller in Gracepoint yet I don't hear the unusual "American" Accent that was used. Is it because I watched Broadchurch first...possibly.   Or maybe I just prefer the Scottish accent over the, uh, different sounding, American one...(I am not judging...I could not fake an accent to save my life so yea.)

Other than that I can't place where the accent comes from.  Whose English voice am I using when I read?!?!!??!  Whose Canadian accent is that?!?!  I don't know anyone from Boston... Mid-western...how does one define that when they are from the South?!!??!  Scottish...there is a huge difference between the way Sean Connery and Ewan McGregor sound (at least to me).  How does it work (in your head)???  I mean there are so many!!! The females voices aren't mine, I don't think... How does our brain determine what characters sound like as we read, hmmm.  If I see a movie before I read the book, I am fairly certain the voices I "hear" are those of the actors but what about the other way around.  I read Hunger Games before the movies came out...my Katniss didn't sound like Jennifer Lawrence, she sounded more mousey in my head... not sure why.  Probably because they said over and over how she really didn't want to be noticed.  She was independent but  didn't want to be a leader.  In my head that gave her a softer, less authoritative voice, I guess. 

I'm sure much of it depends on the authors description but still.  And yes I know dialects differ across countries...hello an "American accent" could mean any number of things.  It boggles the mind!!!  I thought about it because today we were talking about sexy accents and Jamie Dornan came up.  He has a nice smooth Northern Irish accent (I had to look that up...I don't know the difference), very alluring.  But in my head when I am told "Irish Accent" they sound more like the brothers from Boondock Saints.  Which is still sexy but in a whole other way.   I just don't know!!! Someone tell me where the voices in my head come from!!!

OMG, I sound like a complete basket case right now.  Maybe I need a nap...I think I am over thinking this...