Picture this:

You watch a crime.

You are interviewed.

You give a statement about what you saw.

Do you think that at a later date you would be able to detect whether someone had tampered with your statement? Or re-written parts of it?

This is currently a hot topic in the UK, where recent Inquest and Inquiry into the ‘Hillsborough disaster’, in which 96 people were crushed to death during a soccer match in 198, found that 164 testimonies had been deliberately altered by police.

Research published earlier this year by the false memory dream team at the University of California, looked directly into the implications of such police (mis)conduct. They found that it is possible that changed statements can go unnoticed by the person who gave the original testimony, and may even develop into a false memory that accommodates the false account.

To describe this effect, the researchers came up with the term ‘memory blindness’ - the phenomenon of failing to recognize our own memories. The term was intended to mirror the ‘choice blindness’ literature. Choice blindness is forgetting choices that we have made. The researchers wanted to know “Can choice blindness have lasting effects on eyewitness memory?”

To examine this, PhD Student Kevin Cochran and his colleagues conducted two experiments.

In the first study, they showed 186 participants a slideshow of a woman interacting with three people, one of whom stole her wallet. 15 minutes after ‘witnessing’ this pickpocketing, participants were asked a number of questions designed to be similar to what a police officer would ask. Questions included “what color was the thief’s jacket?” and “how tall was the thief?”

After another 15-minute delay, participants were shown their responses to the memory questions. However, three of their responses had been randomly changed. The participants were shown this misinformation as if it was their actual response, and were asked follow-up questions. For example, when shown the answer to “what color was the thief’s jacket?” the misinformation would suggest that they had chosen a different color than they had actually picked.

Then, after a final 15-minute delay, the participants were asked to respond to the same memory interview that they had first been given. This allowed the researchers to see whether or not the participants had changed their answers to be in line with the wrong information.

Although you may think that you could remember your own memories, these findings suggest that often you don’t. The majority of participants in this study failed to notice that their responses had been altered, and many changed their answers on the second memory test to be in line with it.

In the second study, the researchers asked 379 participants to follow a very similar procedure, except that this time the slideshow showed a man stealing a radio from a car, and instead of being asked about what happened, participants were asked to identify the thief out of a photo lineup. In this study, the misinformation was telling participants that they had picked a different person out of a lineup than the man they had originally identified.

On this occasion, 53.7% of participants changed their answer in their final lineup to be in line with the false feedback (of those who did not correctly guess what the study was about). This means that the majority of people readily accepted that they had initially picked a completely different suspect than they actually had.

These results are akin to another study from the University of Maastricht that was published in 2014, which also found that many eyewitnesses have memory blindness for faces, particularly after a 48-hour delay.

It would appear that many of us quite readily internalize fake accounts, mistaking manipulated memories with original memories. We are all sometimes memory blind.

Findings like this are particularly problematic for the criminal justice system, which relies on the accuracy of memory accounts every single day. Misinformed witnesses may be prone to changing their accounts without knowing that they are doing so. Courts should treat such evidence cautiously, particularly when we know that the police have in the past knowingly engaged in a process of ‘review and alteration’ for witness statements in such a sensitive case as Hillsborough.