Overjustification Effect

The overjustification effect is a phenomenon where providing external incentives for an already intrinsically motivating activity diminishes a person’s intrinsic motivation to perform that activity. This effect occurs because the external reward shifts the perceived source of motivation from internal (interest, enjoyment) to external (reward, compensation).

Key Aspects

1. Definition: The overjustification effect occurs when an external reward decreases a person’s intrinsic motivation to engage in a previously enjoyable activity, leading to a reduction in the frequency or quality of the activity once the reward is removed.

2. Mechanisms:

   • Cognitive Evaluation Theory: Proposes that external rewards can undermine intrinsic motivation by shifting the locus of causality from internal (self-determined) to external (controlled by others).
   • Self-Perception Theory: Suggests that individuals infer their motivation by observing their behavior and the context in which it occurs. When external rewards are introduced, they infer that they are engaging in the activity for the reward rather than for personal enjoyment.
   • Attribution Theory: Explains that people attribute their behavior to external rewards rather than to intrinsic interest, leading to reduced internal motivation.

Experimental Evidence

1. Lepper, Greene, and Nisbett (1973):

   • Experiment: Preschool children who enjoyed drawing with markers were divided into three groups: one expecting a reward, one receiving an unexpected reward, and one with no reward.
   • Results: The group expecting a reward showed a significant decrease in intrinsic motivation (less time spent drawing) compared to the other two groups, demonstrating the overjustification effect.

2. Deci (1971):

   • Experiment: College students were paid to complete puzzles they initially enjoyed. After the payment was discontinued, their engagement with the puzzles dropped significantly compared to a control group that was never paid.
   • Results: This demonstrated that external rewards could reduce intrinsic motivation and interest in the activity.

3. Marker Study with Children:

   • Setup: Similar to Lepper et al., children were given markers to play with, with some expecting rewards.
   • Findings: Consistently showed that expected rewards led to decreased engagement with the activity once the rewards were no longer available.

Mathematical Formalization

To formalize the overjustification effect, consider the following model based on motivation:

1. Intrinsic Motivation ($M_i$):

   • Let $M_i$ be the intrinsic motivation for an activity, which can be represented as a positive utility function $U_i(A)$ of the activity $A$.
   • $M_i=U_i(A)$

2. Extrinsic Motivation ($M_e$):

   • Let $M_e$ be the extrinsic motivation due to an external reward $R$, which can be represented as another utility function $U_e(R)$.
   • $M_e=U_e(R)$

3. Total Motivation ($M_t$):

   • The total motivation for the activity when both intrinsic and extrinsic factors are present:
   • $M_t=M_i+M_e=U_i(A)+U_e(R)$

4. Effect of External Rewards:

   • The introduction of an external reward $R$ changes the perceived motivation, and when the reward is removed, the intrinsic motivation may diminish:
   • $M_i^{\prime }=U_i(A)-\delta$
   • where $\delta$ represents the reduction in intrinsic motivation due to the overjustification effect.

5. Net Motivation Post-Reward:

   • After the reward is discontinued, the net motivation becomes:
   • $M_t^{\prime }=M_i^{\prime }=U_i(A)-\delta$

Implications

1. Education:

   • Educators should be cautious in using external rewards for activities that students already find intrinsically motivating, as it might reduce their long-term interest in learning.

2. Workplace:

   • Employers should consider the potential negative impact of incentives on employees’ intrinsic motivation, particularly for tasks that employees find inherently satisfying.

3. Parenting:

   • Parents should be aware that rewarding children for activities they already enjoy, such as reading or playing sports, might reduce their intrinsic interest in these activities.

Related Concepts

• Intrinsic Motivation
• Extrinsic Motivation
• Self-Perception Theory
• Cognitive Evaluation Theory
• Attribution Theory

Understanding the overjustification effect is crucial for designing environments and interventions that promote sustainable intrinsic motivation without undermining it with excessive external rewards.