You can hear nothing. Any information you recieve must be communicated in writing or sign language. You have a -1D penalty to KNO towards learning non-native languages, but get a +1D on any gesture or sign language or lip reading, with the bonus at most the amount the skill is over the attribute. As another option, a player of a deaf character may wear earplugs to force the other players to write notes or use sign language. This isn't very practical, but can be interesting. The GM may talk to the player whenever he wants, however.