In this kind of models, there is an implicit assumption that intrinsic and extrinsic rewards are additive. .
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2.2. Attribution and Self-Perception Theory .
The foundations of this approach rest on the idea that individuals are not a priori, knowing why they behave as they do, that is, they do not have a direct access to the knowledge of their own motivation. Consequently they try to deduce them from post behavioral inferences. More precisely, Bem (1967, 1972) assumes that "to the extent that internal states are weak, ambiguous, or uninterpretable, individuals must look at their own behavior and the situation in which it occurs to interpret their attitudes and motivations" Amabile, Hill, Hennessy and Tighe, 1994, p. 951). The attribution of the performance can indeed be internal or external. .
In the first case, the locus of causality (or locus of control, a theory due to Rotter (1966)) is the individual himself, his own effort or his ability; in the second, the individuals ascribe their performance to their environment (external locus of causality). It could therefore happen that strong incentives hide some potential propensity to perform a task for reasons of intrinsic motivation and then discourage the future performance of this task. In fact the individual believes that he performs this task because he is extrinsically motivated and not because the task is interesting by itself. As far as the crowding effect is concerned, the self-perception perspective puts forward that the cognitive reevaluation of an activity Ÿs intrinsic characteristics due to the misattribution of one Ÿs causes, leads to changed expectations and attitudes towards this activity. .
Accordingly, it is better for people to labor without aid and under the less conspicuously external influences than to be helped and strongly rewarded. The experiments made to validate this theoretical approach (as many of the experiments corroborating the crowding out effect) concerns children at school.