Loftus and Palmer (1974): Car Crash Experiment

Psychologist Elizabeth Loftus has been particularly concerned with how subsequent information can affect an eyewitness’s account of an event.

Her main focus has been on the influence of (mis)leading information regarding both visual imagery and wording of questions concerning eyewitness testimony.

A leading question is a question that suggests what answer is desired or leads to the desired answer.

Loftus’ findings indicate that memory for an event that has been witnessed is highly flexible.  If someone is exposed to new information during the interval between witnessing the event and recalling it, this new information may have marked effects on what they recall.  The original memory can be modified, changed or supplemented.

The fact that eyewitness testimony can be unreliable and influenced by leading questions is illustrated by the classic psychology study by Loftus and Palmer (1974), Reconstruction of Automobile Destruction, described below.

Aim

To test their hypothesis that the language used in eyewitness testimony can alter memory.

Thus, they aimed to show that leading questions could distort eyewitness testimony accounts and so have a confabulating effect, as the account would become distorted by cues provided in the question.

To test this, Loftus and Palmer (1974) asked people to estimate the speed of motor vehicles using different forms of questions.

Estimating vehicle speed is something people are generally poor at, so they may be more open to suggestions.

Experiment One:  5 verbs in leading questions

Procedure

Forty-five American students from the University of Washington formed an opportunity sample.

This was a laboratory experiment with five conditions, only one of which was experienced by each participant (an independent measures experimental design).

Seven films of traffic accidents, ranging in duration from 5 to 30 seconds, were presented to each group in random order.

After watching the film, participants were asked to describe what had happened as if they were eyewitnesses.

They were then asked specific questions, including the question “About how fast were the cars going when they (smashed / collided / bumped / hit / contacted) each other?”

Thus, the IV was the verb of the question, and the DV was the speed reported by the participants.

Findings

The estimated speed was affected by the verb used. The verb implied information about the speed, which systematically affected the participants’ memory of the accident.

Participants who were asked the “smashed” question thought the cars were going faster than those who were asked the “hit” question.

The participants in the “smashed” condition reported the highest speed estimate (40.8 mph), followed by “collided” (39.3 mph), “bumped” (38.1 mph), “hit” (34 mph), and “contacted” (31.8 mph) in descending order.

Conclusion

The results show that the verb conveyed an impression of the speed the car was traveling and this altered the participants” perceptions.

In other words, eyewitness testimony might be biased by the way questions are asked after a crime is committed.

Loftus and Palmer offer two possible explanations for this result:

1. Response-bias factors: The misleading information provided may have influenced the answer a person gave (a “response-bias”), but didn’t actually lead to a false memory of the event. For example, the different speed estimates occur because the critical word (e.g., “smash” or “hit”) influences or biases a person’s response.
2. The memory representation is altered: The critical verb changes a person’s perception of the accident—some critical words would lead someone to perceive the accident as more serious. This perception is then stored in a person’s memory of the event.

If the second explanation is true, we expect participants to remember other details that are not. Loftus and Palmer tested this in their second experiment.

Experiment Two: The broken glass manipulation

A second experiment was conducted with the aim of investigating is leading questions simply create a response bias, or if they actually alter a person’s memory representation.

Procedure

150 students were shown a one-minute film which featured a car driving through the countryside followed by four seconds of a multiple traffic accident.

Afterward, the students were questioned about the film. The independent variable was the type of question asked.

• 50 participants were asked “how fast were the car going when they hit each other?”,
• 50 participants were asked, “How fast were the cars going when they smashed each other?”
• the remaining 50 participants were not asked a question about the car’s speed (i.e., the control group).

One week later, the dependent variable was measured – without seeing the film again, they answered ten questions, one of which was a critical one randomly placed in the list:

“Did you see any broken glass? Yes or no?”

There was no broken glass in the original film.

Findings

Participants were asked how fast the cars were going when they smashed were more likely to report seeing broken glass.

Conclusion

This research suggests that questioning techniques easily distorts memory, and information acquired after an event can merge with original memory, causing inaccurate recall or reconstructive memory.

The results from experiment two suggest that this effect is not just due to a response bias because leading questions altered the participant’s memory for the event.

The addition of false details to a memory of an event is referred to as confabulation. This has important implications for the questions used in police interviews of eyewitnesses.

Consequently, Loftus and Palmer support the reconstructive memory hypothesis – arguing that information gathered at the time of an event is modified by data gathered afterward.

Over time, information from these two sources is integrated so that it is impossible to separate them—in effect, we have only one memory.

Strengths

High level of control

Perhaps the greatest strength of Loftus and Palmer’s experiment is the degree of control over confounding variables. As the study was lab-based, the researchers could ensure that a range of factors (age of participants, incident viewed, environment, etc).

Consequently, they could ensure that these factors did not affect the respondents’ answers and that only the verb condition was causing the participants to reevaluate their memories.

Practical Implications

The reconstructive memory hypothesis is extremely useful as a psychological explanation, for instance, in formulating guidelines for police questioning witnesses and suspects.

The conclusion that leading questions can affect memory has important implications for interviewing witnesses, both by police immediately or soon after an event and also by lawyers in court sometime later.

Interviewers should avoid leading questions and be careful to word questions in a way that does not suggest an answer to the person they are interviewing.

The study also had real-world implications; based on evidence such as Loftus’s, the Devlin Report (1976) recommended that trial judges instruct juries that it is not safe to convict on a single eyewitness testimony alone.

Replicable

Low ecological validity

One limitation of the research is that it lacked mundane realism / ecological validity. Participants viewed video clips rather than being present at a real-life accident.

As the video clip does not have the same emotional impact as witnessing a real-life accident, the participants would be less likely to pay attention and less motivated to be accurate in their judgments.

Furthermore, watching a real crash provides much more context—the participants were cued to watch the video, whereas crashes in real life are largely unexpected.

In an experiment, you may expect to be asked questions about what you are watching, which may make you attend the film differently.

In real life, the answers you give may have consequences, which may put pressure on the witness.

Overall, we can probably conclude that this laboratory experiment had low ecological validity and thus may not tell us very much about how people’s memories are affected by leading questions in real life.

Conflicting research

A study conducted by Yuille and Cutshall (1986) conflicts with the findings of this study. They found that misleading information did not alter the memory of people who had witnessed a real armed robbery.

This implies that misleading information may have a greater influence in the lab rather and that Loftus and Palmer’s study may have lacked ecological validity.

He was especially interested in the characteristics of people whom he considered to have achieved their potential as individuals.

Biased Sample

A further problem with the study was the use of students as participants. Students are not representative of the general population in several ways.

Demand Characteristics

Participants know they are in a laboratory experiment, which will affect their behavior in several ways. They will be looking for clues on how to behave (demand characteristics), and they will usually want to help the experimenters by giving them the results they think they want.

We cannot know that the leading questions had irretrievably altered the participants’ original memories.

Instead, participants could merely be following the researcher’s suggestions in both the original round of questions and the follow-up questions.

In effect, demand characteristics could be “carried forward” – as participants remembered being asked about the cars “smashing” into each other, they were prompted to say that they had seen broken glass in the follow-up study.

References

Devlin Committee Report: Report of the Committee on Evidence of Identification in Criminal Cases, 1976 Cmnd 338 134/135, 42

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.

Yuille, J. C., & Cutshall, J. L. (1986). A case study of eyewitness memory of a crime. Journal of Applied Psychology, 71(2), 291.