In March, I had a marvelous visit to Sylviane's lab in Grenoble. She does very interesting work on string processing in dyslexia, and has shown that dyslexics are able to report fewer letters per fixation than unimpaired readers. We both agree that this is related to a deficit in the ability to allocate visual attention, although we have somewhat different interpretations. She thinks that dyslexics have a general deficit in the ability to allocate attention across multiple objects, whereas I think that dyslexics have a covert-attention deficit that interferes with letter-string processing in particular.
However, like many things in neuropsychology, there may be multiple contributing factors. Sylviane showed me some individual data that convinced me that some dyslexics do indeed have trouble distributing attention over more than one or two objects. I suspect that there are probably other subjects whose deficit is specific to letter strings.