What is consciousness?

Patient P.S. suffered a stroke that damaged the right side of her brain, leaving her unaware of everything on her left side. If someone threw a ball at her left side, she might duck. But she wouldn't have awareness of the ball or know why she ducked. Where does consciousness come from? Michael Graziano explores the question that has vexed scientists and philosophers for centuries. [Directed by TED-Ed, narrated by Addison Anderson].