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Story highlights

The woman who accused Brett Kavanaugh of assault says he and another person were drunk during the alleged incident

How exactly can alcohol affect eyewitness memory? Experts weigh in

(CNN) —  

Supreme Court nominee Brett Kavanaugh and the woman who has accused him of physical and sexual assault, California professor Christine Blasey Ford, have indicated a willingness to testify about the allegations before the Senate Judiciary Committee. If they do they will likely face questions about how reliable memory can be when alcohol is involved. The science says that alcohol can play a role in memory recall depending on the amount and how much time has gone by.

Kavanaugh has repeatedly denied allegations that he assaulted Ford at a party during his high school years in the early 1980s when she was 15. Ford has said there was one other person in the room when the alleged incident took place: Kavanaugh’s then-classmate, Mark Judge. In a letter to the Senate Judiciary Committee, Judge’s lawyer says his client has “no memory of this alleged incident.”

Earlier this summer, in a letter written to Sen. Dianne Feinstein, Ford wrote that both men were drunk during the assault.

Judge has not been invited to testify and through his lawyer says he does not wish to speak publicly regarding the allegations. But Judge’s reported lack of recollection of the alleged event could become a focal point for all those looking into the accusation. Judge, now a journalist and filmmaker, wrote the book “Wasted: Tales of a Gen X Drunk,” where he details his experiences of extensive drinking while attending Georgetown Preparatory School with Kavanaugh.

How much Kavanaugh, Ford and Judge were drinking – if at all – on the night of the alleged assault may lead to questions of whether alcohol plays a role in how much they recall.

Several experimental studies – published in the journals Law and Human Behavior, Memory, and Applied Cognitive Psychology, among others – have found that intoxicated eyewitnesses with a low to moderate blood alcohol concentration were just as reliable as sober witnesses in the quantity, and quality and accuracy of their witness statements and accuracy. More research is needed to determine just how drastically that reliability could change if a an eyewitness had been consuming more alcohol, binge drinking, or even blacked out.

How heavy drinking can impair memory

“When people experience blackouts, they have ‘gaps’ in their memories that they then try to piece together to create a personal narrative. To reconstruct what they don’t remember, people may use factual information, as well as how they believe that an event should have happened,” said Kim Fromme, a professor of clinical psychology at the University of Texas at Austin and director of the Studies on Alcohol, Health, and Risky Activities Laboratory.

“From a scientific standpoint, people in a blackout can still behave voluntarily and make personal decisions, even if those decisions may not be judged as good ones,” said Fromme, who has no relation to the Kavanaugh case.

“He or she might decide to drive home from a bar, climb onto a roof, or purchase airline tickets online. All [are] actions requiring complex thought processes, but are decisions the person later may not remember and could regret,” she said.

So blackouts are periods of amnesia people experience while intoxicated, during which they are still capable of participating in conversations or behaviors but might not remember.

“It is unclear how these acute episodes of alcohol-induced memory loss impact memory in the long-term,” said Mary Beth Miller, assistant professor in the department of psychiatry at the University of Missouri School of Medicine in Columbia, who has no relation to the Kavanaugh case.

It turns out that a rapid increase in blood alcohol concentration is most consistently associated with the likelihood of a blackout, according to research.

Binge drinking is when you drink so much alcohol in a short amount of time that it brings your blood alcohol level to about 0.08%. It can take about four drinks for women or five for men consumed within about two hours for that to occur, according to the National Institute on Alcohol Abuse and Alcoholism.

“Any behavior that quickly increases blood alcohol concentration – taking shots [for example] – would also be expected to increase the likelihood of blackouts,” Miller said.

“There also seems to be a biological component to blackouts, such that some people are more likely to experience blackouts than others,” she said. “They may be born with a predisposition for blackouts.”

Alcohol can lead to memory impairment by decreasing the electrical activity of the neurons in your hippocampus, the part of the brain responsible for the formation of short-term memories.

“To create a memory, we first attend to sensory input, such as someone’s voice, which is transferred to short-term memory, and is then transferred to long-term memory for later retrieval,” Fromme said.

“Alcohol can impair all aspects of memory,” she said. “But most critically it impairs the transfer of information from short-term memory – what are we talking about now – to long-term memory, what did I say to him or her yesterday?”

’Intoxicated witnesses were best when recalling immediately’

A study, published last year in the journal Law and Human Behavior, investigated how reaching around a 0.08% blood alcohol content may affect memory and recall.

A sample of 249 undergraduate students were randomized into groups where they either consumed alcohol; thought they consumed alcohol but really consumed juice; or knowingly consumed juice. Next they watched a mock crime take place.

Some of the study participants were then asked about the crime immediately, while others were asked a week later.

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The researchers found that, after a delay, intoxicated witnesses provided less accurate information than sober witnesses, but were best when recalling information immediately compared to one week later.

In other words, the data suggest that alcohol’s impact may be strongest under conditions when memory is already weaker, because of the time delay.

“Intoxicated witnesses were best when recalling immediately, suggesting that allowing witnesses intoxicated at the .07% level to be interviewed sober one week later may be detrimental to witness accuracy,” the researchers wrote in the study.

They noted their study comes with some limitations. “Extrapolating from basic research on alcohol’s effect on memory and cognition may prove difficult,” they wrote, because the methodologies and materials used in research still may not be completely reflective of the real world, for instance.

Overall, they wrote, “future research needs to disentangle more specifically the respective importance of low versus moderate versus high intoxication levels” and how each may impact your memory.

CNN’s Ariane de Vogue, Eli Watkins, Sophie Tatum, and Sandee LaMotte contributed to this report.