Blurry is probably not the correct word... it really is a focus like looking through a camera ... some of it is sharper than others. It is difficult to come up with a word to describe a change in focus. Have you ever seen a photo where the background is in terrific sharp focus and the people or object in front looked softer... not as sharp... they are still clear and recognisable... how would you decribe it.... kinda blurry? When you photoread thats the kind of mental snapshots you are trying to take.
It is a case of where the attention is. What you notice (and I have your experience too) is that the words are still legible near where we are focusing through the book... and this is one reason it is often suggested that the book be photoread upside down... so as not to lose photofocus and get caught up in recognising words because once you start recognising words you slip into refocusing more of the text.
The thing is the inner mind still recognises letter forms right way up or upside down. It's not so much the letters themselves but the white space that surround the letters that helps us to recognise letter and groups of letters that form words because of the shape that is the white space. Really when the letters appear "blurry" it is because the focus is going into that white space past the letters themselves.
Alex
