In contrast, second-generation models of prosocial behavior propose a possible interaction
between material incentives and prosocial motivation. A rst approach assumes a change in
preferences due to an external intervention. Research from psychology posits that incentives
can undermine the intrinsic motivation for a task (Deci and Ryan, 1985; Lepper and Greene,
1978). The basic idea is that incentives change the way individuals think about an activity: if
incentives are used, performing the activity may impair perceptions of self-determination or selfesteem
and thus the level of prosocial motivation. Overall, a lower level of activity may result.
These mechanisms and potential applications in economics are discussed more extensively in
Frey (1997) and Frey and Jegen (2001). A formalization of the approach can be found in Frey