I have seen and experienced the following phenomena. It often happen in a work environment but can happen anytime and anywhere:
1) Person A is doing something that requires full concentration (like reading or thinking deeply).
2) Person B suddenly ask/say something to Person A
3) Person A replied with "What do you say?" or "Pardon please" (or something similar, as if he/she doesn't hear what person B said) after some brief pause/delay.
4) Person B didn't answer back (optional)
5) Person A answers/responses (before Person B repeats what he/she said) to Person B (as if he/she heard it fully)
Is there a psychological term that describes/explain it? How it is happening? What is its effect with the brain of Person A if there is?
P.S. I don't know what is the right tag for it.