Wednesday, July 02, 2008

How much do eyewitnesses really see?

How much of what an eyewitness "sees" represents inputs from the outside world, and how much of it is constructed by the brain?

My layman's grasp of new brain science currently revolutionizing views of human cognition remains spotty at best, but much of what's coming out on the topic appears to have implications for the criminal justice arena. Take, for example, the debate over the best procedures for gathering eyewitness identification, long considered the gold standard (or perhaps silver, after a confession) for gaining a conviction in court. Scientists are learning that to a great extent what we see is constructed by the brain from memory instead of reflecting an image of the outside world.

In an extensive article in the June 30 New Yorker on the brain and itching ("The Itch" - not online but see discussions here and here), surgeon and author Dr. Atul Gawande writes that:
[T]he more we examine the actual nerve transmissions we receive from the world outside, the more inadequate they seem.

One assumption had been that the sensory data we receive from our eyes, ears, nose, fingers, and so on contain all the information that we need for perception and that perception must work something like a radio. It's hard to conceive that a Boston Symphony Orchestra concert is a radio wave. But it is. So you might think that it's the same with the signals we receive - that if you hooked someone's nerves to a monitor you would watch what the person is experiencing as if it were a television show.

Yet, as scientists set about analyzing the signals, they found them to be radically impoverished. ...

The images in our mind are extraordinarily rich. We can tell if something is liquid or solid, heavy or light, dead or alive. But the information we work from is poor - a distorted, two-dimensional transmission with entire spots missing. So the mind fills in most of the picture. You can get a sense of this from brain anatomy studies. If visual sensations were primarily received rather than constructed by the brain, you'd expect that most of the fibres going to the brain's primary visual cortex would come from the retina. Instead, scientists have found that only twenty percent do; eighty percent come downward from regions of the brain governing functions like memory. Richard Gregory, a prominent British neuropsychologist, estimates that visual perception is more than ninety percent memory and less than ten percent sensory nerve signals.
So what we see in the heat of the moment is a "radically impoverished" version of reality and our minds fill in the blanks from memory. No wonder faulty eyewitness identifications turn out to be the single leading cause of wrongful convictions among DNA exonerees! This also helps explain why witnesses are more reliable identifying someone they knew before the crime - their memories have more data from which to construct the scene. It's when identifying strangers, primarily, that limitations on eyewitness identification come most starkly into play.


Anonymous said...

I've been jumped at gunpoint, and again a few years later at knifepoint. Perhaps it was because I was suprised both times but I could identify the weapons but not their faces. I guess my brain just naturally focused my eyes on the most important detail of the situation

Ryan Paige said...

I've had two or three short conversations with my neighbor down the block. If you asked me to pick him out of a line-up of similar-looking men, I don't think I could (and, like I said, I've been face-to-face with him in calm situations where I was able to look directly at him for several minutes).

Unknown said...

My 25 years as a trial lawyer (exclusively civil) lead me wonder if anyone knows the physiological processes involved as effective advocates secure the improbable surprise outcome from an initially skeptical jury.

In search of answers to that mystery, I joined Yahoo's groups on neurosciences and the San Antonio based Mind Science Foundation. I've learned of a few advances in that area, which suggest the day is fast approaching when traditional trials will be no more.

The devaluation of eyewitness testimony has even more support and that is the subject of an episode from Radio Lab, a PRI affiliated production coming out of WNYC. Hear it at

You'll learn of Dr. Elizabeth Loftus' finding that 25% of the people studied were susceptible to the implantation of entirely false memories. She's a psychologist at U.C. Irvine, and her studies go back 2 decades.

Also, Joe LeDoux and Karim Nader, NYU neuroscientists, discovered the mechanics of how memories are formed: proteins. As I recall, when we remember something, the entire experience we think is a discretely stored "event" is, in fact, a newly created production comprised of bits of data that are transfered from our "memory" cells into proteins which then are arranged in our minds "eye" as a complete memory. Each time we do this, the final product is missing more and more data, which gets filled in by other proteins from closely stored cells or in some cases from our "imagination" taking cues from any number of different sources - such as the suggestive questions of an interrogator.

During the memory's formation, the final product isn't in place, so the memory is "unstable" as Karim Nadir puts it. If false data is available to fill in the missing pieces, the mind will add it to the memory, rather than confess to its having been forgotten.

Another scientist whose discoveries are likely to change how we mete out justice is V.S. Ramachandran. The lecture he gave in San Antonio for the Mind Science Foundation is called the Artful Brain, and it's available here:

Dr. Ramachandran was also a featured scientist on Radio Lab's first show of the 2005 season, entitled "Who am I," at this URL: (

"The Artful Brain" lecture concerned Dr. R's findings that suggest only 20% of our tastes in art are unique and subjectively derived by the individual's preferences. The remaining 80% of what causes us to like a given work comes from our genetic propensities to respond emotionally and intellectually to certain patterns, colors, shapes, etc., and the popular artists are those who intuitively figure out what our primal "visual language" is and then exploit it through their various media.

The notion that we can be subliminally seduced has been around for decades, but Ramachandran is homing in on the mechanics by which we may be able to do it with precision and predictability.

Cagey trial lawyers are probably already using various "tricks" to maximize their clients' advantage with arrays of seemingly random displays designed to affect a positive response in the jury, just when the controversial testimony is being admitted.

Great site you've got here, which I found out about from Debbie Russell's posted comment on the lawyer who simulated masturbation and was held in contempt. Here's that site:

Anonymous said...

the best procedures for gathering I think the devaluation of eyewitness testimony is also of great import in relation to not only eyewitness identification but also in just recounting an event as witnessed. I am a student of the events of 9-11 and have read studies of the eyewitnesses and what they said they saw. I believe what is constructed from memory becomes even less reliable when the event witnessed is horrifying and monumentally "terrifying."

Anonymous said...

As a trained investigator with over 20 years in the field, I can attest empirically to the almost complete unreliability of eyewitness testimony. As a student of human observation, I have read many studies that tested the validity of eyewitness accounts in controlled situations. Without exception, these studies found eyewitness accounts to be highly unreliable.
Crime scenes are by their very nature emotionally highly charged. That high emotional content can only serve to worsen the reliability of eyewitness accounts.