Voice of America has a report about a study that looked at how deaf people read versus how hearing people read. What the study found, is that signing deaf people do not silently "hear" a word when they read, but instead "see" the sign language representation in their heads. I don't think this is anything new; I recall reading similar statements before. What's different is that this study likens signing deaf people learning to read, to hearing people learning English as a second language.
However, I have to agree with the "silent hearing" part. Since I grew up oral, I find that when I read, I am literally "sounding" the words to myself in my head. It makes sense that a signing deaf child would not "sound" the words to themselves but instead visualize the signing equivalency.
It also helps me understand why phonetics are so important for both hearing and deaf. If you learn phonetics, you can "silently sound" words to yourself even if you don't really know how to pronounce the word. Who knows how many words I am pronouncing wrong because I have not heard the correct pronunciation? The point is, when I read a strange word, I can "sound" it to myself even though I have not heard it.
Of course, this does not answer all the questions about why many deaf people struggle with English, but it does offer a partial answer.
