Mark Lepper has done a lot of research on intrinsic motivation, including the classic studies showing that external rewards can undermine intrinsic motivation. You can see what looks most relevant in this list of his papers, or search Google scholar with those keywords (Lepper intrinsic motivation).
There is also some recent research on choking, I believe by Dan Ariely, which shows that people do some tasks worse with large incentives than with small incentives because of the pressure to succeed.
Mark Lepper has done a lot of research on intrinsic motivation, including the classic studies showing that external rewards can undermine intrinsic motivation. You can see what looks most relevant in this list of his papers, or search Google scholar with those keywords (Lepper intrinsic motivation).
There is also some recent research on choking, I believe by Dan Ariely, which shows that people do some tasks worse with large incentives than with small incentives because of the pressure to succeed.
retracted