Subvocalization

There is a general tendency to subvocalize when reading becomes difficult, when we can predict less.—Understanding Reading, page 167

<idle musing>
I hadn't really thought about it before, but it is true. Now that I think about it, I remember sitting in a graduate seminar and the professor was referring to a German reference work. He didn't just subvocalize it, he muttered it as he was trying to figure out exactly what they were saying—mind you, this was about a text in an ancient language that we were all struggling with, so it wasn't the German that was tripping him up, it was the ancient language :)
</idle musing>