09 April 2009

What really happened?

Our memories are remarkably open to manipulation, something which may compromise a lot of eye witness testimony, researchers say.


You are 100% sure Max wasn't there that day 10 years ago when you almost drowned in the ocean. Your partner is equally sure he was.

Our memories are unreliable, and we have a hard time accepting that – that’s nothing new. But, recent studies suggest, our memories may be more iffy than even our partners think: it transpires memory is remarkably open to manipulation.

This is not necessarily a big issue in much of our day-to-day lives – who cares if Max was really at the beach that day? – but getting the details of the past wrong can have serious consequences in the courtroom.

What the eye witness saw
In a recent study reported in the journal Psychological Science, researchers tested how easily eyewitnesses could be made to change their minds about their memory of the crime.

For the experiment, the researchers from John Jay College and Iowa State university staged a crime scene.

A small group of student-subjects were made to sit in a university laboratory, apparently waiting for an experiment to begin. An unknown person was then made to walk in, pick up a laptop, and leave the room. A few minutes later, the research assistant would enter the room, look around, and let it be known, with obvious distress, that her laptop was missing. The group of students, eyewitnesses to the event, were enlisted to identify the thief from a line-up.

Identifying the ‘thief’
The line-up did not, in fact, include the person who had actually taken the laptop. Still, at the identity parade, the majority of the students did ‘recognise’ one of those in the line-up as the thief. They were asked to rate how confident they were in their choice of ‘thief’.

Two days later, the students were asked to return to continue helping with the investigation. They were told either that all of the suspects denied involvement, or that a specific ‘suspect’ had confessed. The students were asked to reconsider their original identification, and rate how confident they were now.

The results cast an unsettling light on the integrity of eyewitness testimony.

Since none of those in the line-up was in fact the real thief, the only reliable testimony came from those who had fingered no one. Very few did: the vast majority of study volunteers identified an innocent man as the criminal, and many did so with confidence.

Memories adapt
That's disturbing in itself, but it gets worse. While few were persuaded by claims of innocence, a full 60% of those eyewitnesses who had identified the ‘thief’ changed their minds with the confession on the table.

Even those who had said they were very sure of their original identification flip-flopped, and experienced a steep drop in confidence. When asked to explain their change of heart, most said they had been mistaken earlier, that their memories had fooled them.

How about the rare volunteers who (correctly) refused to finger anyone? These witnesses would seem to be especially cautious about falsely accusing someone of a crime. Yet fully half of them also changed their minds when told a specific suspect had confessed.

The study authors conclude that, ‘Once informed of a confession, an eyewitness is forever tainted.’

These findings have serious implications for our legal system, particularly in light of the fact that many confessions are not credible. According to one estimate, fully a quarter of convictions later overturned by DNA evidence involve a false confession.

While some come from mentally disturbed attention seekers, say experts, they can also be motivated by someone wanting to take the fall for someone else. But most innocents who confess do so under stress, as an act of surrender, during a high-stakes, high-pressure police interrogation.

This study shows how a false confession can be cemented with subsequent false eye witness testimony.

Tainting the facts
False confessions are not the only threat to accurate eyewitness testimony though. According to a Psychological Science press release, studies have shown that when people are given false information about an event, they become less likely to remember what actually happened. It is easy to mix up the real facts with fake ones. You might, for instance, think that you saw a white man running, but when someone else says it was a black man, you might start to wonder.

In a second study, also published in Psychological Science, researchers from Iowa State University, Tufts University and Rhode Island College wanted to see how providing false information in the wake of a recall test would affect volunteers' memories of an event they witnessed. A group of volunteers watched the first episode of the television show "24", and then either took an immediate recall test about the show, or played a game. Next, all of the subjects were told false information about the episode they had seen; and then took a final memory test about the show.

The researchers found that the volunteers who took the test immediately after watching the show were almost twice as likely to recall false information than were the volunteers who played a game following the episode. The results of a follow-up experiment suggest that the first recall test may have improved subjects' ability to learn the false information - that is, the first test enhanced learning of new and erroneous information.

These findings show that recently recalled information is prone to distortion. The authors conclude that "this study shows that even psychologists may have underestimated the malleability of eyewitness testimony".

The clock everyone forgot
False recall doesn't only happen to individuals, it can also happen to groups – something which makes sense if they were all exposed to the same disruptive stimulus.

A recent report published in the journal Cortex relates a remarkable instance of mass misremembering. It involved a bomb that killed 85 people at a station in the Italian city of Bologna in 1980.

The station clock stopped at 10:25 on the morning of the explosion. It was repaired soon after. When the clock broke in 1996, authorities decided not to fix it, and to set it to 10:25 in remembrance of the 1980 bomb attack.

Of 180 people working at or regularly using the station – the experiment chose people old enough to have lived through the time of the bomb attack – 160 believed that the clock had been broken since the bomb attack, and of them, 127 believed it had been stuck on 10:25 since the bombing. In other words, most people simply erased from their memories the 16 years in which the clock worked perfectly well.

One possible reason for this is that it simply wasn't necessary for people to consult the clock during those 16 years, and they simply projected their memories to span the period when it had worked.

Thus, when you ask people working at the station about the clock, the answer you are most likely to get is that it had not worked since 1980. "Why, ask anyone," you might be told. And if you ask around you'll be told the same thing. But the thing is, they'd all be wrong.

(Marcus Low, Health24, April 2009)

Note: Parts of this story were compiled from Psychological Science press releases.


Witness for the prosecution? The effect of confessions on eyewitness testimony (The full study is published in the January issue of Psychological Science)

Did I see what I think I saw? (The full study is published in the January issue of Psychological Science)

de Vito S, Cubelli R, Della Sala S. Collective representations elicit widespread individual false memories. From the May 2009 issue of Cortex. (Originally picked up on at Ben Goldacre's BadScience blog)


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