[mwexler]

The early Festinger (1959) studies are basically this exact point. Getting paid or paying transforms an internally driven experience into an externally driven one (get paid or deal with fines). Later studies generalized, but the idea that "external reward or punishment is involved" changes perception of the task from internally reward driven to external, due to the dissonance of "why I'm doing it."

The economists have their own name for many phenomena that come down to the same thing that the psychologists would predict. Hence the rise of "behavioral economics" to converge the fields.