Stanford marshmallow experiment
Original Stanford experiment
This first experiment took place at Stanford University in 1970. The participants were 32 children. The children were led into a room, empty of distractions, where a treat of their choice (either two animal cookies or five pretzel sticks) were placed on a table. The researchers let the children know they could eat the treat, but if they waited 15 minutes without giving in to the temptation, they would be rewarded with a second treat. Mischel and Ebbesen observed, "(some children) covered their eyes with their hands, rested their heads on their arms, and found other similar techniques for averting their eyes from the reward objects. Many seemed to try to reduce the frustration of delay of reward by generating their own diversions: they talked to themselves, sang, invented games with their hands and feet, and even tried to fall asleep while waiting - as one successfully did."
Then the experimenter returned to the experimental room and opened the cake tin to reveal two sets of rewards (in the form of edibles): five pretzels and two animal crackers. The experimenter asked the child which of the two they preferred. Once the child chose, the experimenter explained that the child could either continue to wait for the more preferred reward until the experimenter returned, or the child could stop waiting by bringing back the experimenter. If the child stopped waiting then the child would receive the less preferred reward and forgo the more preferred one.
Depending on the condition and the child's choice of preferred reward, the experimenter picked up the cake tin and along with it either nothing, one of the rewards, or both. The experimenter returned either as soon as the child signaled him to do so or after 15 minutes.Results
The results indicated the exact opposite of what was originally predicted. Instead of the rewards serving as a cue to attend to possible delayed rewards, the rewards themselves served to increase the children's frustration and ultimately decreased the delay of gratification. The results seemed to indicate that not thinking about a reward enhances the ability to delay gratification, rather than focusing attention on the future reward.
Stanford marshmallow experiment
The following study, conducted by Mischel, Ebbesen, and Zeiss (1972), is generally recognized as the Stanford marshmallow experiment due to its use of marshmallows as a preferred reward item. Building on information obtained in previous research regarding self-control, Mischel et al. hypothesized that any activity that distracts a participant from the reward they are anticipating will increase the time of delay gratification. It was expected that overt activities, internal cognitions, and fantasies would help in this self-distraction. Through such distraction it was also hypothesized that the subject would be able to take the frustrative nature of the situation and convert it into one psychologically less aversive. To test their expectations, the researchers contrived three settings under which to test participants; an overt activity, a covert activity, or no activity at all.
They predicted that under the overt and covert activities that delay of gratification should increase, while under the no activity setting it would decrease. To assess the children’s ability to understand the instructions they were given, the experiment asked them three comprehension questions; “Can you tell me, which do you get to eat if you wait for me to come back by myself?”, “But if you want to, how can you make me come back ?”, and “If you ring the bell and bring me back, then which do you get?” Three distinct experiments were conducted under multiple differing conditions.
Experiment 1 participants
The participants consisted of 50 children (25 boys and 25 girls) from the Bing Nursery School at Stanford University. They ranged in age from 3 years 6 months to 5 years 6 months. The mean age was 4 years 6 months. Six subjects were eliminated because they failed to comprehend the instructions given by the experimenters.
Experiment 1 procedures
The procedures were conducted by one male and one female experimenter. During the test conditions the male experimenter conducted his session with 3 male and 2 female participants, while the female experimenter conducted her session with 3 female and 2 male participants. The small room where the tests were conducted contained a table equipped with a barrier between the experimenter and the child. On the table, behind the barrier, was slinky toy along with an opaque cake tin that held a small marshmallow and pretzel stick. Next to the table equipped with the barrier there was another table that contained a box of battery and hand-operated toys, which were visible to the child. Against one wall of the small room there was a chair, another table, and a desk bell.
In Experiment 1 the children were tested under the conditions of (1) waiting for delayed reward with an external distractor (toy), (2) waiting for delayed reward with an internal distractor (ideation), (3) waiting for a delayed reward (no distractor), (4) external distractor (toy) without delay-of-reward waiting contingency, and (5) internal distractor (ideation) without delay of reward contingency.
Experiment 2 participants
The participants consisted of 32 children from the Bing Nursery School of Stanford University. They ranged in age from 3 years 9 months to 5 years 3 months. The mean age was 4 years and 9 months. Six of the subjects were eliminated from the study because they failed to comprehend the instructions or because they ate one of the reward objects while waiting for the experimenter.
Experiment 2 procedures
Experiment 2 focused on how the substantive content of cognitions can affect subsequent delay behavior. The conditions in Experiment 2 were the same as in Experiment 1, with the exception that after the three comprehension questions were asked of the children the experimenter suggested ideas to think about while they were waiting. These suggestions are referred to as “think food rewards” instructions in the study. They were intended to induce in the subject various types of ideation during the delay-of-gratification period.
Experiment 3 participants
The participants consisted of 16 children (11 boys and 5 girls). They ranged in age from 3 years 5 months to 5 years 6 months. The mean age was 4 years 6 months.
Experiment 3 procedures
In Experiment 3 all of the conditions and procedures were the same as in Experiment 1 and Experiment 2, except that the reward items were not visible to the children while they waited. In the previous experiments both of the reward objects were directly available to the children while they waited in the delay period. To achieve this change in condition the children were told that the food items needed to be kept fresh. The marshmallow and pretzel stick were then placed under the opaque cake tin and put under the table out of sight of the child. In this experiment the same “think food rewards” were given to the children as in Experiment 2.
The three separate experiments demonstrate a number of significant findings. Effective delay of gratification depends heavily on the cognitive avoidance or suppression of the reward objects while waiting for them to be delivered. Additionally, when the children thought about the absent rewards, it was just as difficult to delay gratification as when the reward items were directly in front of them. Conversely, when the children in the experiment waited for the reward and it was not visibly present, they were able to wait longer and attain the preferred reward. The Stanford marshmallow experiment is important because it demonstrated that effective delay is not achieved by merely thinking about something other than what we want, but rather, it depends on suppressive and avoidance mechanisms that reduce frustration.
The frustration of waiting for a desired reward is demonstrated nicely by the authors when describing the behavior of the children. “They made up quiet songs…hid their head in their arms, pounded the floor with their feet, fiddled playfully and teasingly with the signal bell, verbalized the contingency…prayed to the ceiling, and so on. In one dramatically effective self-distraction technique, after obviously experiencing much agitation, a little girl rested her head, sat limply, relaxed herself, and proceeded to fall sound asleep.”
Watts, Duncan and Quan's 2018 conceptual replication yielded mostly statistically insignificant correlations with behavioral problems but a significant correlation with achievement tests at age 15. These effects were lower than in the original experiment and reduced further when controlling for early cognitive ability and behavior, family background, and home environment.
A 2020 study at University of California showed that a reputation plays significant role in the experiment.