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How reliable is eyewitness testimony?

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Home // Monitor on Psychology // April 2006 Monitor on Psychology // How reliable is eyewitness testimony?

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Feature

How reliable is eyewitness testimony?

Psychologists are helping police and juries rethink the role of eyewitness identifications and testimony.

By
Zak Stambor

Monitor Staff

April 2006, Vol 37, No. 4

Print version: page 26

On Oct. 10, 1997, Fairbanks, Alaska, residents who had lived in the state at least a year received about $1,500-an equal share of the income produced by the sale of state’s oil and other natural resources. Residents receive these oil dividends, in part, to keep them vested in their state government.

Inevitably some residents raucously celebrate the annual windfall, and that night the celebrating turned deadly as four young hooligans embarked on “Clockwork Orange”-style attacks on random individuals. When the night was over, a teenage boy, John Hartman, had been robbed, sexually assaulted and murdered, and an older man, Franklin Dayton, was seriously injured after being robbed and attacked.

Within days, four suspects were arrested and locked up. At the trial two years later, the prosecutor’s case rested on an eyewitness account by Fairbanks resident Arlo Olson, who testified that as he stood in the doorway of Eagles Hall, he watched in horror as a group of men, whom he identified as the defendants, accosted and savagely beat Dayton in a parking lot 450 feet away.

“No physical evidence actually ties any of the defendants to the crimes,” wrote Fairbanks Daily News-Miner reporter Larry Campbell in an article on the trial.

The defense called as an expert witness Geoffrey Loftus, PhD, a University of Washington perception and cognition psychology professor who testified that Olson was too far away to accurately perceive the defendants’ facial features. Seeing someone from 450 feet away is like sitting high in the center field bleachers in Yankee Stadium and looking across the ballpark at another individual sitting in the stands behind home plate, Loftus testified.

Despite Loftus’s testimony, the jury convicted the defendants of assault and murder. Four years later, the defense attorney learned that the jury had believed Olson’s identification because four jurors had conducted an illegal and unauthorized experiment in broad daylight: They paced out what they thought was 450 feet. And once one juror suggested that she could see clearly, it negated Loftus’s testimony, the defense attorney said. As a result, the conviction was sent to an appeals court where it remains in litigation.

Mistaken or flawed identification has assumed a newfound prominence in recent years: It’s been cited as a factor in nearly 78 percent of the nation’s first 130 convictions later overturned by DNA testing, according to the New York-based Innocence Project, which works to free the wrongly convicted. As a result, a number of researchers are turning their attention to helping police departments and juries better understand the circumstances under which eyewitnesses observe crimes and later identify a suspect.

Distance creates blurriness

Soon after testifying in the Fairbanks trial, Loftus began seeking a way to visually present to juries the proposition that people’s ability to decipher details degrades rapidly as a person or object moves further away.

“At 10 feet, you might not be able to see individual eyelashes on a person’s face,” he says. “At 200 feet, you would not even be able to see a person’s eyes. At 500 feet, you could see the person’s head but just one big blur. There is equivalence between size and blurriness-by making something smaller you lose the fine details.”

In a 2005 article in the journal Psychonomic Bulletin & Review (Vol. 12, No. 1, pages 43-65), Loftus examined his distance-as-filtering hypothesis that, as a face moves further away, its details become progressively courser and more difficult to recognize.

In the study, Loftus and Erin Harley, PhD, a postdoctoral fellow at the University of California, Los Angeles, conducted a series of experiments with participants who had 20/20 vision or corrected 20/20 vision. They presented participants with small, unrecognizable images of famous people like Julia Roberts, Michael Jordan and George W. Bush, and gradually enlarged the images until the participants could identify each person. The researchers then recorded the size at which each participant recognized the celebrity and then converted this size to a corresponding real-life distance. In another part of the study, Loftus and Harley started with blurred images of the celebrities and then gradually clarified them until the participants could recognize them. The researchers then recorded the amount of blurring that the made the face recognizable.

Comparing the relationship between losses in clarity due to size or blurriness allowed Loftus to develop a formula to approximate the amount of detail people who have 20/20 vision lose at a range of distances in normal daytime light.

“We know enough about the visual system that we now can create a visual depiction of what is lost at any given distance,” Loftus says. “When an image is far away, the image shrinks in size on the retina and, as a result, loses details.”

The formula, Loftus says, allows expert witnesses-like himself-to use a specific mathematical relationship between image quality and distance to visually simulate the conditions under which an eyewitness observed a crime.

“As an expert witness, my aim is not to use absolute judgment, but to provide as much information as possible,” Loftus says. “This tool provides a visual aid to show a jury the best possible view that a witness might have had.”

A new spin on eyewitnesses

Iowa State University experimental social psychologist Gary Wells, PhD, a member of a 1999 U.S. Department of Justice panel that published the first-ever national guidelines on gathering eyewitness testimony, says Loftus’s model suggests that crime investigators need to think about eyewitness evidence in the same way that they think about trace evidence.

“Like trace evidence, eyewitness evidence can be contaminated, lost, destroyed or otherwise made to produce results that can lead to an incorrect reconstruction of the crime,” he says. Investigators who employ a scientific model to collect, analyze and interpret eyewitness evidence may avoid incidents like Olson’s potentially flawed identification of the Fairbanks suspects, he notes.

In fact, Wells says that other evidence techniques, such as police lineups, are similar to scientific experiments. In lineups, the police have a hypothesis, they provide instructions, collect responses and interpret the results. As such, the same factors that can bias the results of an experiment can bias an eyewitness’s performance in picking suspects out of a lineup, he says.

In a 2000 American Psychologist (Vol. 55, No. 6, pages 581-598) article that dovetailed with the Department of Justice report, Wells and his colleagues outlined a number of ways police can avoid biasing eyewitness testimony, including warning the witness that the actual perpetrator may or may not be in a lineup, maintaining a double-blind lineup environment so that a detective cannot influence a witness’s judgments and securing a statement of the witness’s certainty of their identification.

“To a research psychologist, the changes seem obvious,” he says. “But to law enforcement officials they are very different from how they’ve tended to do things in the past.”

Since the publication of both the American Psychologist and Department of Justice pieces, states such as New Jersey, North Carolina and Wisconsin have incorporated many of the recommendations, including one in the Department of Justice report that advises law enforcement officials to warn eyewitnesses that the culprit’s appearance may have changed since the crime.

However, Wells challenges that recommendation in an upcoming article in Law and Human Behavior. In the study, he presented participants with a video of a crime involving four culprits. Then, he asked the participants to identify the culprits from four six-person arrays that either included or did not include a culprit. He found that the instruction actually increased the participants’ number of misidentifications.

“The instruction seems to loosen the criterion of eyewitnesses and increases their propensity to identify someone,” he says. “Eyewitnesses start to imagine possible changes and think, ‘This must be him.'”

Wells is optimistic that such psychological research can have a profound impact on both police’s evidence-gathering practices and on how courtrooms inform juries-like the Fairbanks jury-of the possibility that flaws may exist in eyewitness accounts.

“The system [of interpreting eyewitness accounts] will never be perfect, but psychological research can help make it a lot better,” he says.

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Memory › EWT

Eyewitness Testimony

Saul McLeod , published


Eyewitness testimony is a legal term.  It refers to an account given by people of an event they have witnessed. 

For example they may be required to give a description at a trial of a robbery or a road accident someone has seen.  This includes identification of perpetrators, details of the crime scene etc.

Eyewitness testimony is an important area of research in cognitive psychology and human memory.

Juries tend to pay close attention to eyewitness testimony and generally find it a reliable source of information.  However, research into this area has found that eyewitness testimony can be affected by many psychological factors:

  • Anxiety / Stress
  • Reconstructive Memory
  • Weapon Focus
  • Leading Questions ( Loftus and Palmer, 1974 )
  • Anxiety / Stress

    Anxiety or stress is almost always associated with real life crimes of violence.  Deffenbacher (1983) reviewed 21 studies and found that the stress-performance relationship followed an inverted-U function proposed by the Yerkes Dodson Curve (1908). 

    Yerkes Dodson Curve

    This means that for tasks of moderate complexity (such as EWT), performances increases with stress up to an optimal point where it starts to decline.

    Clifford and Scott (1978) found that people who saw a film of a violent attack remembered fewer of the 40 items of information about the event than a control group who saw a less stressful version.  As witnessing a real crime is probably more stressful than taking part in an experiment, memory accuracy may well be even more affected in real life.

    However, a study by Yuille and Cutshall (1986) contradicts the importance of stress in influencing eyewitness memory.

    They showed that witnesses of a real life incident (a gun shooting outside a gun shop in Canada) had remarkable accurate memories of a stressful event involving weapons. A thief stole guns and money, but was shot six times and died.

    The police interviewed witnesses, and thirteen of them were re-interviewed five months later.  Recall was found to be accurate, even after a long time, and two misleading questions inserted by the research team had no effect on recall accuracy. One weakness of this study was that the witnesses who experienced the highest levels of stress where actually closer to the event, and this may have helped with the accuracy of their memory recall.

    The Yuille and Cutshall study illustrates two important points:

    1. There are cases of real-life recall where memory for an anxious / stressful event is accurate, even some months later.

    2. Misleading questions need not have the same effect as has been found in laboratory studies (e.g. Loftus & Palmer).


    Reconstructive Memory

    Bartlett ’s theory of reconstructive memory is crucial to an understanding of the reliability of eyewitness testimony as he suggested that recall is subject to personal interpretation dependent on our learnt or cultural norms and values, and the way we make sense of our world.

    Many people believe that memory works something like a videotape.  Storing information is like recording and remembering is like playing back what was recorded.  With information being retrieved in much the same form as it was encoded.  However, memory does not work in this way.  It is a feature of human memory that we do not store information exactly as it is presented to us.  Rather, people extract from information the gist, or underlying meaning.

    In other words, people store information in the way that makes the most sense to them.  We make sense of information by trying to fit it into schemas, which are a way of organizing information.

    Schemas are mental ‘units’ of knowledge that correspond to frequently encountered people, objects or situations.  They allow us to make sense of what we encounter in order that we can predict what is going to happen and what we should do in any given situation.  These schemas may, in part, be determined by social values and therefore prejudice.

    Schemas are therefore capable of distorting unfamiliar or unconsciously ‘unacceptable’ information in order to ‘fit in’ with our existing knowledge or schemas.  This can, therefore, result in unreliable eyewitness testimony.

    Bartlett tested this theory using a variety of stories to illustrate that memory is an active process and subject to individual interpretation or construction.

    In his famous study ‘War of the Ghosts’, Bartlett (1932) showed that memory is not just a factual recording of what has occurred, but that we make “effort after meaning”.  By this, Bartlett meant that we try to fit what we remember with what we really know and understand about the world.  As a result, we quite often change our memories so they become more sensible to us.

    His participants heard a story and had to tell the story to another person and so on, like a game of “Chinese Whispers”. 

    The story was a North American folk tale called “The War of the Ghosts”.  When asked to recount the detail of the story, each person seemed to recall it in their own individual way.

    With repeating telling, the passages became shorter, puzzling ideas were rationalized or omitted altogether and details changed to become more familiar or conventional.

    For example, the information about the ghosts was omitted as it was difficult to explain, whilst participants frequently recalled the idea of “not going because he hadn’t told his parents where he was going” because that situation was more familiar to them. For this research Bartlett concluded that memory is not exact and is distorted by existing schema, or what we already know about the world.

    It seems, therefore, that each of us ‘reconstructs’ our memories to conform to our personal beliefs about the world.
     

    This clearly indicates that our memories are anything but reliable, ‘photographic’ records of events.  They are individual recollections which have been shaped & constructed according to our stereotypes, beliefs, expectations etc.

    The implications of this can be seen even more clearly in a study by Allport & Postman (1947).

    When asked to recall details of the picture opposite, participants tended to report that it was the black man who was holding the razor.

    Clearly this is not correct and shows that memory is an active process and can be changed to ‘fit in’ with what we expect to happen based on your knowledge and understanding of society (e.g. our schemas).


    Weapon Focus

    This refers to an eyewitness’s concentration on a weapon to the exclusion of other details of a crime.  In a crime where a weapon is involved, it is not unusual for a witness to be able to describe the weapon in much more detail than the person holding it.

    Loftus et al. (1987) showed participants a series of slides of a customer in a restaurant.  In one version the customer was holding a gun, in the other the same customer held a checkbook. Participants who saw the gun version tended to focus on the gun.  As a result they were less likely to identify the customer in an identity parade those who had seen the checkbook version

    However, a study by Yuille and Cutshall (1986) contradicts the importance of weapon focus in influencing eyewitness memory.

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    References

    Allport, G. W., & Postman, L. J. (1947). The psychology of rumor. NewYork: Holt, Rinehart & Winston.

    Bartlett, F.C. (1932). Remembering: A Study in Experimental and Social Psychology. Cambridge: Cambridge University Press.

    Clifford, B.R. and Scott, J. (1978). Individual and situational factors in eyewitness memory. Journal of Applied Psychology, 63, 352-359.

    Deffenbacher, K. A. (1983). The influence of arousal on reliability of testimony. In S. M. A. Lloyd-Bostock & B. R. Clifford (Eds.). Evaluating witness evidence. Chichester: Wiley. (pp. 235-251).

    Loftus, E.F., Loftus, G.R., & Messo, J. (1987). Some facts about weapon focus. Law and Human Behavior, 11, 55-62.

    Yerkes R.M., Dodson JD (1908). The relation of strength of stimulus to rapidity of habit-formation. Journal of Comparative Neurology and Psychology, 18: 459–482.

    Yuille, J.C., & Cutshall, J.L. (1986). A case study of eyewitness memory of a crime. Journal of Applied Psychology, 71, 291-301.


    How to reference this article:

    McLeod, S. A. (2009). Eyewitness testimony. Retrieved from https://www.simplypsychology.org/eyewitness-testimony.html


    Further Information

    Cognitive Interview

    Eyewitness Testimony eyewitness testimony pdf

    Elizabeth Loftus and Eye Witness Testimony

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