Memories can't be trusted and become contaminated when people discuss their memories of an event with others, according to a University of Sydney study.

Lead researcher, Dr Helen Paterson from the School of Psychology said sharing memories can contaminate people's recollections and create false memories.

"A false memory is the recollection of an event, or details of an event, that did not actually occur," she said.

"My research focuses on how people can contaminate each other's memories for an event by discussing it with one another."

Dr Paterson said a key finding of the research was that misleading information presented through discussion with another person who observed the event can also lead to memory distortion.

"That is, witnesses who discuss an event with a co-witness are very likely to incorporate misinformation presented by the co-witness into their own memory for the event," she said.

"Once their memory has been contaminated in this way, the witness is often unable to distinguish between the accurate and inaccurate memories.

"Critically, our research has shown that co-witness discussion is an especially potent delivery mechanism for misinformation; information provided during discussions with a co-witness is more likely to be incorporated into the witness's memory than information encountered through leading questions, inaccurate media reports or other processes.

"Furthermore, our research has shown that memory contamination persists, even when people are warned that they have been exposed to misinformation by their co-witness.

"This suggests to us that people sometimes find it difficult, if not impossible, to distinguish between genuine memories and false memories of an event."

Dr Paterson said the research had significant implications regarding the reliability of witness memory.

"Legal procedures are designed to counter dangers which arise when civilian witnesses discuss an event with one another.

"For example, our research has revealed that police officers in Australia often attempt to separate co-witnesses and discourage them from talking about the event with one another. Furthermore, witnesses are often prohibited from hearing each other's testimonies and lawyers may question witnesses regarding whether or not they have discussed the incident with others.

"Despite these attempts to keep witness testimony independent, it is clear that witnesses often do talk to each other about the event. Discussion among witnesses is difficult, if not impossible to prevent."

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Source: University of Sydney