I'll add the weird datapoint that I normally subvocalize, but that I've been aware since age 10 that I can also read prose while singing along to music that I'm familiar with.
I just tried doing this right now and my observations yielded that I appear to not subvocalize when I do this and that I seem to therefore speed up and lose a bit of comprehension/retention. Which is going to be fine in lots of contexts, but is worth being aware of.
http://en.wikipedia.org/wiki/Subvocalization
I'm curious about how often or to what degree visitors to this site subvocalize as they read. I was originally interested in reducing subvocalizations as a way to increase reading speed, as the idea is mentioned in multiple pieces I've read about speed reading.
The Wikipedia entry seems to focus on subtle throat and muscle movements, but I'm more interested to know if you "say" or "hear" the words in your head as you read.
Since reading about subvocalization recently, I seem to notice that I "say/hear" what I'm reading quite frequently. I'm not sure if this is causal (in the way that the command "don't think of pink elephants" obliges you to do so), or if I just notice it more now, or both.
When I'm very engrossed in a book either I don't notice the subvocalizations or they stop happening, so seems that it could either be a cause or a symptom of distractedness.
In the comments, please describe your mental subvocalizations (or lack of them) and if they are related to how engrossed you are in the book. Any other comments relevant comments about speed reading or subvocalizations are welcome.