SarathW wrote:I do not hear sound even when I read a book.
You're still hearing sound, but you're not noticing it because you're engrossed in your book and not paying attention to the background auditory stimuli. It's a form of neural adaptation/habituation. If a sufficiently different and intense auditory stimulus went off near you, say an airhorn, you can bet your butt you'd hear it.
The question here is whether the person in jhana would hear it. My impression is that it depends on what definition of "jhana" we're using.