Accuracy of eyewitness testimony: Is it all in our head?

Eye Witness Identifications

Guy Miles was not a model citizen. In 1998, he’d broken the conditions for parole (he had been incarcerated on charges of stealing cars from a valet parking service) by moving to Nevada from California. Thinking he was still concealing his true whereabouts, he traveled back to California to meet with his parole officer there, and he was subsequently arrested.

But his arrest was not for the parole violation, instead it was for bank robbery. Two eye witnesses to a robbery in Orange County, California, identified Miles as one of the robbers. Despite compelling evidence of Miles’ innocence, he was convicted and sentenced to 75 years in prison. In 2013, however, more evidence (including a confession from a co-defendant in Miles’ trial) that implicated two other men was uncovered which removed Miles from the scene of the crime. His appeal is still awaiting a court decision in California.

More legal reversals
Even in the age of DNA evidence and advanced forensics science, the claims of an eyewitness still carry a lot of weight in court, in the media and in our heads. But reversals of convictions due to later evidence, and revelations of eyewitness misidentifications continue to mount. Of the first 130 convictions that were ever overturned by later DNA evidence, 78 percent of the cases were initially decided via misidentification by witnesses, according to the Innocence Project. In addition, studies have shown that one-third of identified perpetrators were instead “fillers” deliberately put in a police lineup; these “fillers” had nothing whatsoever to do with the crime.

So, is eyewitness testimony worth anything? While the latest headlines and court cases might indicate “no,” neuroscientists and criminal justice scholars say that eyewitnesses can have value, as long as we have a solid understanding of how the brain takes in visual or audio memories and how those memories can change over time.


Memories now, memories later
There are many ways eyewitness testimony and memory can change. In the famous trial of security guard George Zimmerman, accused of second-degree murder in the death of a young black man named Treyvon Martin, witness testimony was very inconsistent:

  • One woman at first said she saw men running in the street and getting into a fistfight. Later, her recount changed to just one person, and she couldn’t remember what he looked like.
  • Another witness said she saw two men wrestling on the ground after the shooting, but couldn’t tell one from the other. Later, her account changed to identifying Zimmerman as the man on top.
  • Recollections of Zimmerman’s appearance changed for one witness, from bloody and in a state of shock, to calm and in control of himself.

For many neuroscientists, the value of eyewitness testimony depends on timing — when testimony was collected, as well as how well the eyewitness truly saw what was happening at the time of the crime.

A lot of how personal accounts are created depend on how the brain stores memories. Richard Wise, a University of North Dakota forensic psychologist, told Scientific American:

To reconstruct a memory, the eyewitness draws upon several sources of information, only one being his or her actual recollection. To fill in gaps in memory, the eyewitness relies upon his or her expectation, attitudes, prejudices, bias, and prior knowledge. Furthermore, information supplied to an eyewitness after a crime (i.e., post-event information) by the police, prosecutor, other eyewitnesses, media, etc., can alter an eyewitness’s memory of the crime.

I’m seeing things
To understand how memories can be filled in, changed and otherwise affected, it’s become important to know how both the eyes and brain work.


The eye, of course, takes in light through the lens and aligns images to the retina. Then, images are picked up and transmitted to the brain, via the optic nerve. At that point, things can get complicated. The brain’s various regions code information, and decide where it should be stored, or how it should be reacted to. This process can result in a number of optical illusions. These illusions, or false

Related article:  Does language change the way our brains see the world?
An MC Escher print
An MC Escher print

images, include spots that arise when the eyes focused on very bright lights, optic migraines that produce shadows or other (nonexistent) light changes, or cognitive illusions, which occur when the eye records one image, but the brain encodes (or “remembers”) another. Prints by MC Escher, or pictures that seem to alternatively show an image of a horse and a tree exemplify this type of illusion.

These illusions can affect how a witness remembers something like a crime and memories can be changed by much more than illusions. A U.S. National Research Council analysis on eyewitness testimony reported in 2014 that:

Factors such as viewing conditions, duress, elevated emotions, and biases influence the visual perception experience. Perceptual experiences are stored by a system of memory that is highly malleable and continuously evolving, neither retaining nor divulging content in an informational vacuum. As such, the fidelity of our memories to actual events may be compromised by many factors at all stages of processing, from encoding to storage and retrieval.

When were you so sure?
Timing of the event may be another issue with eyewitness testimony. In the George Zimmerman trial mentioned earlier, several witnesses changed their story from their initial impressions, but this was not isolated to the Zimmerman case. Scientists have started looking at how certain a witness was of his or her first impressions of a crime; often, if they’re not certain at first, they can later be coaxed (either by their brains or a prosecutor) into greater certainty, even if that certainty is wrong. Conversely, knowing a witness’ certainty during the initial investigative interview can help put that memory into some context.


To remedy these issues, psychologists have teamed up with the U.S. Justice Department (which set up procedures for handling eyewitness accounts only in 1999) and criminal prosecutors to determine how eyewitness evidence is handled. These included procedures that mimic scientific studies, including a warning to witnesses that a suspect may not be in a police lineup, and double-blind situations in which a detective cannot influence a witness’ memory.

But the National Research Council report indicated that far more needed to be done, particularly on the research side. The report criticized inadequate collaboration between police, courts and researchers, cited a lack of transparency of research methods on eyewitness handling, and found a lack of reproducibility with data reporting.

So for now, in eyewitness testimony, what you see isn’t necessarily what you get. But at least now science can show us how what we see changes what we get.

Andrew Porterfield is a writer, editor and communications consultant for academic institutions, companies and non-profits in the life sciences. He is based in Camarillo, California. Follow @AMPorterfield on Twitter.

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