PsychOS
The Deci Experiment: How Paying People to Enjoy Something Can Quietly Kill Their Interest in It
College students who were paid to solve an enjoyable puzzle kept playing with it less on their own time than students who were never paid at all — revealing that a reward can quietly replace genuin...
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Give someone money for doing something they already enjoy, and it seems obvious that they should enjoy it at least as much afterward, if not more. Edward Deci's 1971 experiment found almost the opposite. Paying people for an activity they found genuinely interesting made them less likely to keep doing it once the money stopped, compared to people who had never been paid for it in the first place.
THE HYPOTHESIS
Deci was testing an early version of what would later become self-determination theory, built around a specific and, at the time, fairly radical prediction: external rewards, like money, can undermine a person's intrinsic motivation — their genuine, internally driven interest in an activity for its own sake — particularly when the reward comes to feel like the actual reason for doing the activity, rather than a bonus on top of already-present enjoyment.
His hypothesis ran directly against the dominant behaviorist assumption of the time, which held that reinforcement, in the form of external reward, should straightforwardly increase the frequency of any rewarded behavior. Deci predicted that for activities people already found interesting on their own, adding an external reward could paradoxically decrease their motivation to continue once that reward was removed.
THE METHODOLOGY
Deci recruited college students for what they believed was a study on problem-solving, using Soma puzzles — a genuinely engaging set of interlocking block puzzles many participants found enjoyable in their own right. The study ran across three separate sessions. In the first session, all participants worked on the puzzles with no reward offered, establishing a baseline level of interest. In the second session, one group was told they would be paid one dollar for each puzzle they solved, while a control group continued working with no payment at all. In the third session, the payment was removed for the previously-paid group, and both groups were again given free time with the puzzles and no instructions on what to do with it.
The critical measurement happened during a deliberate gap built into each session: partway through, the researcher would leave the room, ostensibly to retrieve additional materials, leaving participants alone with the puzzles and several unrelated magazines. Researchers secretly observed, through a one-way mirror, how much of this free time each participant spent voluntarily continuing to work on the puzzles versus reading the magazines or doing nothing puzzle-related at all. This free-choice period served as the actual measure of intrinsic motivation — what people chose to do when no reward or instruction was attached to it.
STEP-BY-STEP EXECUTION
In the first, unpaid baseline session, both groups spent a similar amount of their free time voluntarily continuing to work on the puzzles, confirming the activity was genuinely engaging on its own. In the second session, the paid group naturally worked hard on the puzzles, since they were now being compensated per puzzle solved — this session wasn't measuring intrinsic interest, since an external reward was actively present.
The critical result appeared in the third session, after payment had been removed. The previously-paid group now spent noticeably less free-choice time voluntarily working on the puzzles than they had in the very first baseline session, before any money was ever introduced. The control group, who had never been paid, showed no such drop, and in some replications showed a slight increase in voluntary engagement over the same period.
Later work by Deci and colleagues, including a large 1999 meta-analysis conducted with Richard Ryan and Wayne Cameron reviewing over 128 studies, confirmed this undermining effect specifically for tangible, expected rewards tied to task completion, while also clarifying that not all rewards behave the same way — unexpected rewards, and rewards tied specifically to performance quality rather than mere participation, showed smaller or sometimes reversed effects.
PSYCHOLOGICAL REVELATION
Deci's research demonstrated that motivation isn't simply additive — stacking an external reward on top of an already-enjoyable activity doesn't guarantee more enthusiasm for that activity, and can measurably reduce it once the reward disappears. This occurs because the reward can shift how a person mentally explains their own behavior: instead of continuing to think "I do this because I find it interesting," a paid participant may begin to think "I do this because I'm getting paid," a subtle reattribution that quietly erodes the original, internally-generated motivation once the external justification is removed.
[Placeholder interlink — Good Samaritan Study — pending confirmed URL]
This connects to the mechanism explored in Operant Conditioning Explained: Why Rewards Don't Work the Way Most People Think , which examines how reinforcement schedules shape behavior in far more specific and sometimes counterintuitive ways than a simple "reward increases behavior" model would predict. Deci's findings sit alongside that research as a clear case where an entire category of reward, tangible and expected, undermines rather than strengthens the behavior it targets.
It also offers useful context for Dopamine Explained: Why It's Not the Pleasure Chemical Everyone Thinks It Is , since the shift Deci documented, from intrinsic engagement to reward-dependent participation, mirrors the broader pattern in that research where anticipated, expected rewards function differently in the brain's motivational circuitry than novel or uncertain ones.
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Frequently Asked Questions
What is the overjustification effect?
The overjustification effect describes how offering an external reward for an already-enjoyable activity can reduce a person's intrinsic motivation to continue that activity once the reward is removed, a phenomenon first experimentally demonstrated by Edward Deci in 1971.
What did Deci's Soma puzzle experiment find?
Participants paid to solve puzzles they had previously enjoyed for free later spent less voluntary time on those puzzles, once payment stopped, compared to a group that was never paid at all.
Does this mean all rewards reduce motivation?
No. Later meta-analyses found the undermining effect applies mainly to tangible, expected rewards tied to task completion. Unexpected rewards and rewards tied to performance quality showed smaller or sometimes reversed effects.
Why do rewards sometimes reduce intrinsic motivation?
Rewards can shift how a person explains their own behavior to themselves, replacing an internal reason ("I enjoy this") with an external one ("I do this for the reward"), which weakens motivation once that external reward disappears.
Does this apply to real-world settings like school or work?
Yes, self-determination theory research building on Deci's work has been applied extensively to education and workplace motivation, generally suggesting that autonomy-supportive environments sustain intrinsic motivation better than reward-heavy, controlling ones.