If you test people about an event soon after they have witnessed it, it is more likely that their later recall of that event will be suggestible to misinformation or false information, than people who are not tested, said US researchers who found this effect may be good reason to question the recall of some eyewitnesses.

Jason Chan, an Iowa State University (ISU) assistant professor of psychology, and Moses Langley, a former graduate student of ISU who is now a psychology faculty member at the University of Wisconsin-Parkside, conducted two experiments to show the effect of "retrieval-enhanced suggestibility," or RES, on eyewitness recall. A paper on their work was published in the January issue of the Journal of Experimental Psychology: Learning, Memory, and Cognition.

Interested in criminal cases, Chan's and Langley's theory was that eyewitnesses who make a police statement about a crime may have their memory distorted by misinformation by the time they are asked to recall the incident in court. This misinformation can come unknowingly from the police, or from watching or reading news reports about the incidents.

Chan told the press there are many examples of when misinformation is introduced unknowingly into our recall of an event, such as from the police, through friends, and a number of other sources. Also people confuse their memories, even if the information is not specific to the witnessed case.

"For example", said Chan, "if you saw a bank robbery and later saw a movie depicting bank robberies, whatever you remember from that movie - which has nothing to do with the real-life case - can interfere with your ability to recall the real-life case".

As more and more breaking news outlets emerge, for instance with TV and radio trying to compete against instant outlets like Twitter, there is a greater risk that reporters will not have verified their sources, so the scope for misinformation is becoming greater.

To test their theory, Chan and Langley carried out two experiments.

In the first one they invited 78 ISU students to watch a 43-minute pilot episode that they had not seen before from "24", the FOX tv series.

Half of the participants then completed a recall test of questions about the episode while the rest played Tetris, the popular video game.

All the participants then listened to an 8-minute audio summary of the video that contained some false information about the crime they had observed in the pilot episode.

A week later, all the participants then returned and completed the recall test (so for half of them, this was the second time).

The results showed that the participants who were tested just after they had seen the episode were more likely to recall the misinformation from the audio summary.

In the second experiment, 60 students underwent a similar sequence except this time they listened to the audio summary a week after seeing the pilot episode, and then as before, completed the recall test (again, for half the group, this was the second time of doing the test).

The results showed an even stronger RES effect in the participants who were tested just after they saw the pilot episode.

Chan said they were surprised that taking the immediate test, or being asked to recall the event, somehow increased people's susceptibility to misleading information later on.

He and his colleagues were expecting to see evidence that being asked to recall an event would cause people to be less susceptible to misinformation, because that is "what we know from the burgeoning cognitive psychology literature on the testing effect", said Chan.

"That was definitely not expected," he said.

As part of each experiment, some participants from each group did not listen to the audio summary, so they were not exposed to the misinformation. Chan and colleagues found that the participants who completed the initial test recalled the events more accurately than their untested counterparts a week later. So in this case, without the intervention of misinformation, it appears that the initial test reinforced their memory of the events.

Chan said that testing for memory does two things: it not only reinforces recall of the original information, it also makes it easier to learn new information (something anyone who has used Tony Buzan's exam revision techniques can attest to).

However, this "dual benefit" is counterproductive when misinformation steps into the picture.

"... under a situation when you present people with new information that is misleading, it can enhance their learning of that misleading information," said Chan.

"The misinformation is more likely to be recalled if people don't question the accuracy of that new information," he added.

This is the third study that Chan has published on RES, the earlier two were in 2009 (Psychological Science) and 2010 ( Journal of Memory and Language).

He says this work is more important now, because of "all this new misinformation that's floating around".

"Paradoxical effects of testing: Retrieval enhances both accurate recall and suggestibility in eyewitnesses."
Chan, Jason C. K.; Langley, Moses M.
Journal of Experimental Psychology: Learning, Memory, and Cognition, Vol 37(1), Jan 2011, 248-255
DOI: 10.1037/a0021204

Additional source: Iowa State University (7 Feb 2011).

: Catharine Paddock, PhD