Medical advances have improved the odds of surviving a severe traumatic brain injury (TBI) thereby increasing demands for rehabilitation. Medical rehabilitation management during coma recovery, however, has been hampered by a paucity of rigorous clinical trials examining rehabilitation effectiveness. This randomized clinical trial addresses this knowledge gap. The purpose of the study is to determine whether a high dose of familiar vocal stimulation (FVs) improves outcomes for persons who are unconscious after severe TBI. The research objectives are to: