The scandal over the “Joyce Hatto” piano recordings that turned out to have been copies of other artists’ work begs some interesting questions. “Whether you are a master teacher, an opera buff, a concertgoer or a critic, knowing something of the background of the artist you are hearing will inevitably affect your perceptions.” So, when the artist you think you’re listening to turns out to be someone else entirely, your impressions of the entire performance can turn on a dime.