I don't know if this has any relevance for your family, but DH and DD are dyslexic. DH was never diagnosed or remediated. From what he describes and I observe, I think he reads almost entirely by sight words/ seeing every word as a distinct picture (from similarities to DS, I think DH has visual spatial and memory off the charts). He speaks the words in his head while reading, and thus reads at the same speed, whether out loud or silently (or upside down, for that matter).
I wonder if saying the word in his head may be necessary to transform it from the picture he stores into something verbal that can be read?
DD has been through reading remediation, and now decodes far better and reads much faster than her father. I'm guessing she no longer subvocalizes, simply based on her speed.
