23 month old son not responding to his name !?

He honestly seems healthy and normal. The name thing is a little odd, but maybe its just the fact that he is not used to hearing it. Honestly it takes alot of repetitiveness and time for a child to learn their name. If he was never called it much then its no suprise. The fact that he responds to directions indicates he doesn't have a hearing problem. I would use his name with him as much as you can, show him a picture of himself point to it and say his name and point to him and say thats you, Billy, or look in the mirror and say, Mama, and Billy, etc.