Interesting psychology experiments 2: Car crash study


In 1974, Elizabeth Loftus and John Palmer from the University of Washington conducted two experiments [1] investigating the effects of the words used in a question about an event on the memory the participants had of this event.

In the first experiment, the participants were shown several car crashes and were afterwards asked to estimate at which speed the cars collided. Previous studies indicated that humans are surprisingly bad at estimating the speed of cars. After watching films of cars colliding, the participants were given a questionnaire concerning the accident. One question was “About how fast were the cars going when they X?” X was the variable in this case. The participants were divided in five groups, all having a different ‘X’ in their question: (1) contacted, (2) hit, (3) bumped, (4) collided and (5) smashed. The hypothesis was that the choice of verb can have an influence on the speed estimated.

Their results indicate that this was the case; the choice of word had a statistically significant effect on the speed estimate. The largest difference was found for ‘contacted’ vs. ‘smashed’ (about 9mph). While these results confirm their hypothesis, it is unclear whether this was merely due to response bias or due to a real modification of the memory the participants had of the accidents.

Therefore, a second study was conducted: Participants watched a film of a multiple car accident and filled out a questionnaire, again including a speed estimate, afterwards. This time, the participants were divided in three groups: (1) One group being asked about the speed during the accident using the verb ‘smashed’, (2) one group being asked about the speed during the accident using the verb ‘hit’ and (3) a control group not being asked about the speed during the accident at all. The speed estimates for ‘smashed’ vs. ‘hit’ were again significantly different, as expected on the basis of experiment one.

One week later, participants were asked to fill out another questionnaire including several questions concerning the accident. One of these questions was: “Did you see any broken glass?” There was no broken glass on the film, but the hypothesis was that the ‘smashed’ group might report having seen broken glass because they estimated the accident to occur at a higher speed – making the involvement of broken glass more likely. Their results confirmed this: People in the ‘smashed’ group were significantly more likely to report having seen broken glass than people in the ‘hit’ and ‘control’ groups.

This suggests that a memory of an event can be modified by things as simple as different wordings in questions about the event. While this particular study suggests high flexibility of memory, it is difficult to draw conclusions from it for real life events because it occurred in a laboratory study, including only films of accidents. As noted here [2], there was a study concerning eyewitness testimony showing relatively constant and accurate memory of an emotional event over time. This casts doubt on whether memory is as flexible as the Loftus and Palmer experiments suggested if important real life events are concerned.

This blog post is part of the series “Interesting psychology experiments”.
See also:
Interesting psychology experiments 1: The marshmallow experiment
Interesting psychology experiments 3: Contagious yawning works with dogs

[1] Loftus, E. F., & Palmer, J. C. (1974). Reconstruction of auto-mobile destruction: An example of the interaction between language and memory. Journal of Verbal Learning and Verbal Behavior, 13, 585-589
[2] McLeod, S. A. (2010). Loftus and Palmer

Interesting psychology experiments 1: The marshmallow experiment


In the late 1960s, Professor Walter Mischel from the Stanford University started a set of studies investigating delayed gratification in young children. [1]  In the original studies, the procedure was the following: Children, between 3 and 5 years old, were given a marshmallow and were told that they would get a second marshmallow if they wait long enough and don’t eat the first one. The time until the child started eating the marshmallow was measured, the upper limit being 15 minutes because then the experimenter came back with the promised second marshmallow.

Interestingly, follow-up studies showed that the duration of time the children waited for the second marshmallow correlated with the achievements of them many years later. Children who waited longer than others in this experiment tended to  have more success in school, higher SAT scores, lower BMI (Body Mass Index), higher income and more successful marriages later in life.[2]

The common interpretation of these findings was that self-discipline is the factor causing the different times children are waiting during the experiment. The idea behind this is that high self-discipline carries on into later life and enables the children to have a more successful life.

This interpretation was questioned by a recent study with a relatively low sample size. This study wanted to investigate whether rational decision making in the form of the assessment of the reliability of the environment is also an important factor. Previous studies indicated that uncertainty about the arrival of the second marshmallow decreases waiting time. This study specifically intended to test the difference in waiting times for two different conditions: The reliable and the unreliable condition. Their hypothesis was that children in the reliable condition will view the situation as more reliable and therefore wait longer, the opposite being expected for children in the unreliable condition.

The researchers changed the protocol to include the reliable and unreliable conditions in their experiment: Before starting the actual marshmallow task, they completed two different aspects of the experiment. First, the experimenter brought a very limited set of crayons and a piece of paper to the room where the child was sitting and said that he could bring additional crayons from the other room. The child naturally wanted more crayons and in the reliable condition they received those soon while in the unreliable condition the experimenter apologized and said that no additional crayons were in the other room. This was repeated with a sticker: In the reliable condition the experimenter brought a larger sticker from the other room while in the unreliable condition the child had to use a smaller sticker despite being promised a larger one. Afterwards the marshmallow task was completed in the way described above.

Their findings were statistically highly significant: The children in the reliable group waited for a mean time of 12 minutes and 2 seconds while the children in the unreliable group waited for a mean time of 3 minutes and 2 seconds. This supports their hypothesis that the child’s assessment of the reliability of the situation is a contributing factor to the duration of time waited.  This also has implications for the original findings: Depending on the background of the children their belief in the reliability of the world can differ, resulting in a different duration of time they wait. While this doesn’t imply that self-discipline isn’t also a contributing factor, it indicates that it’s not the only one.

To sum up, the marshmallow experiment is a surprisingly efficient predictor of the success of children later in life. Early interpretations of this included mainly self-discipline as the cause of both the longer waiting time and the later success in life while a recent study suggests that the explanation is a more complex one and has to include the ability to make rational decisions.

This blog post is part of the series “Interesting psychology experiments”.
See also:
Interesting psychology experiments 2: Car crash study
Interesting psychology experiments 3: Contagious yawning works with dogs

Photo source: wikimedia

Two new blog post series

I’m delighted to announce that I’m going to start two new blog post series now. The first one will be called ‘Myths about veganism’, dealing with and commenting on several common myths such as ‘vegans don’t get enough protein’ or ‘cows have to be milked’. This way I hope to bring the truth or untruth behind these myths to the attention of more people. I’ll post on one myth at a time so I’m able to go into some detail without making too long posts. 

While veganism and animal rights are very important to me, I don’t want this blog to be solely about these topics, so the second blog post series is going to focus on another interest of mine: Psychology. It is going to be called ‘Interesting psychology experiments’ and will go into some depth about such experiments – again one at a time. 

While I already have several posts in mind for both blog post series, I’m open to suggestions, so if you know a vegan myth or a psychology experiment you would like to see me write on, please let me know in the comments. Don’t forget to ‘follow’ in order to see these upcoming blog post series.