Whose author voice does my book use, and how do I change it?

From version 1.9.24, the Voice card on the book's page names the author whose voice is used, for example: Written the way "Jane Doe" writes, with the profile's name when it is different. Press "Change" next to it to open Book details on the "Author & publisher" list and pick another profile. When the author voice is switched off on the Authors page, or the author has none yet, the card says so, with the same "Change" link.