Well, my Mika dog is deaf from birth and I am HOH. I noticed with her when we first adopted her, that she is "all eyes" on everything. Besides being a herder breed, she is intense in using her eyes. Watches *everything* from facial expressions to body language. Especially my hands as I learned dog training hand signs w/ a few ASL signs thrown in, to communicate with her for commands like sit, down, stay. We made up signs for "good dog" and "go outside?"
So, when my husband & I are practicing our ASL lessons, poor Mika goes nutso because she doesn't know the signs and is trying to figuring out what the heck we are trying to tell her. She still doesn't quite get it, that we're not giving her signs, but giving each other signs.
I have become even more observant with my eyes, too, just like Mika. I watch mouths/faces when people talk to me, and I look for clues in body language, facial expressions, etc. I am also always scanning my surroundings when I'm out and about as well since I may not hear someone/something coming up from behind me or off to the side where I'm not looking or facing.