A kind of memory contamination can emerge from combining questions and mugshots, according to a social experiment by researchers at Florida Atlantic University.

By encountering pictures of faces and questions of criminality at the same time, a false association in a witness’ mind can be created, essentially forming fake memories, contend two scientists from Florida Atlantic University in a recent issue of the journal Memory and Cognition.

“Eyewitnesses remember the crime itself and remember seeing a familiar person before but they may incorrectly visualize these two pieces of information together,” said Alan Kersten, co-author, a psychologist at Florida Atlantic University. “Because they are able to place the familiar person in the context of the crime scene, this may lead them to confidently assert that they saw the person commit the crime.”

A group of 120 people—80 FAU undergraduates with a median age of 19, and 40 elderly volunteers with a median age of 71—were presented with a mixture of actions, allegations and pictures. They were all presented with several dozen short videos of actors performing simple actions. They were later given an assortment of 84 mugshots involving those actors—and also others who had been shown but not doing the actions.

Both the older and younger group were likely to incorrectly recall who did what - if the actors were also included among the mugshots.

The seniors were more likely to erroneously identify a face, based solely off seeing the mugshot before.

The younger people, however, were only more likely to make a false ID if they had a mugshot and questions about an action emerge in the course of the trials.

Several mechanisms could underpin the memory contamination of false association. The “commitment effect” means a witness is likely to stick with a face they have previously selected from a six-pack or other group of mugshots. A factor of “context-free familiarity” means that a witness may mistakenly forge a connection between a familiar face and a crime scene. The third mechanism is making an association between seeing the face in a mugshot while also encountering the information from questions or other speech—thereby forging a link between the two for future questioning and testimony.

“False recollection is really troubling from a legal perspective because this type of memory leads an eyewitness to put a face to a context of a crime scene, incorrectly linking the two together and leading to the conclusion that this person committed the crime,” said Julie Earles, another FAU psychologist who co-authored the study.

A case the psychologists referenced was the conviction of Walter Snyder for a 1985 rape in Alexandria, Virginia. Snyder was not identified in the first weeks of the investigation - but the victim lingered on his picture and mentioned his eyebrows. She later saw him in person at the police station and identified him, leading to his arrest nand conviction. DNA later conclusively exonerated him, after seven years in prison.

The latest study has limitations, the psychologists write. For instance, the participants in the recollection experiments saw a large number of actions and people all at once, while a single crime could be a significantly different experience. Perhaps most significantly, though, would be the “distinctiveness” of a criminal act in the context of otherwise ordinary life.

“Most notably participants were not presented with emotionally laden criminal acts, but rather with simple everyday actions,” they write.

Hundreds of false convictions in the U.S. over the last two decades based on false eyewitness testimony have been overturned by DNA evidence.

Witness testimony has consequently been more rigorously questioned in U.S. courtrooms than ever before. Eyewitnesses are now expected to be handled in a controlled and scientific manner, without allowing the possibility of suggesting details of a crime—so-called “memory contamination.” A recent study by psychologist John Wixted from the University of California San Diego found that initial confidence in identification determined how accurate the testimony ultimately was deemed. “Memory contamination” can result from police questioning and other attempts at recall, contended the study, in the Proceedings of the National Academy of Sciences in December 2015.