Am reading a great book about motivation written by Daniel King that looks at motivation. So mindblowing for animal trainers. It questions the efficacy of motivation being killed by reward and punishment. It is talking about this in the field of human psychology, however we know that this has great relevance in the field of animal psychology.
Basically, in a nutshell, we need to look at the fact that using rewards or punishers to motivate behaviour can hand the responsibility for that behaviour to the person with the power - the motivator as it were. So, our intrinsic motivation or desire is diminished by our lack of perceived choice in the presence of the desire for reward or fear of punishment.
Mmm. So much to think about. Watch this space!!!