Sometimes it seems like this is exactly what's going on at my house. Sandie in particular is guilty of this. I tell her no barking, reassure her that there is no one here or that it's Dad about to come in. They know the sound of his truck, It's a diesel. I know they hear him coming down the road before I do. They start barking early, then I realize they heard it a half mile a way.
Then the crazy thing is later, you can be calling them to come in over and over and they really do not seem to hear you. They look up finally as if to say "oh, did you say something?" "Let me just sniff this blade of grass for another minute and I'll be right with you." Good thing they're sweet and cute and loving and all that stuff or there might be a problem.
Miss Peaches is doing really well since her back surgery, she can be the champ of not listening, but she's not the biggest barker. Now the challenge is to keep her from doing too much now that she is feeling better. I have taken up sleeping on the floor so that she is safe. She has been sleeping with people since she was a pup and is not doing the crate thing at night. So I will get down to her level. The tough part is making the floor not feel like the floor.