<I've been reading Edward Deci's book _Why We Do What We Do_. I've only
read the first three or four chapters, but those focus directly on
studies of intrinsic vs. extrinsic motivation. I think this speaks
fairly directly to what you want to know, as unschoolers avoid pushing
externally motivated learning on their kids. I recommend you see if
your library has this book, and dip into it a little.>

Excellent book!! This is the book that really helped me with the
rewards/punishment issue and arbitrary limits!!!