Children who are promised a payoff for playing with an interesting toy have later been observed to play with the toy less than those who are not promised the reward. this overjustification effect provides evidence for the role of in operant behavior.

Intrinsic motivation

Explanation:

Intrinsic motivation explains the concept that somethings which are to be done by an individual for their own interest and that it is done by them, without even getting any rewards, then when they are offered any rewards then it tends to loose their interest and then develop the interest for rewards rather then the activity they are performing.

Thus, when children are awarded some reward for there favorite activity of playing with their favorite toy, then they tend to loose the interest and rather develop the interest for toy.