Protests in front of the Phi Kappa Psi fraternity house at the University of Virginia on Nov. 22. (Ryan M. Kelly/Charlottesville Daily Progress via AP)

The past year has featured a wrenching national discussion about sexual assault in America -- from debates over how to address the problem in the military, to the allegations against Bill Cosby, to the recent Rolling Stone article examining an alleged gang rape of a female freshman at the University of Virginia. That latter story has faced intense criticism after The Washington Post, in two in-depth articles, reported on significant factual discrepancies in the story. The magazine has since apologized for publishing it.

Separate from the details of the UVa situation or any other, the national dialogue has raised many questions about how victims of sexual assault remember details and how police and other authorities respond to allegations. Largely missing from that discussion, however, have been extensive references to the scientific research done on these topics, which has shown that sexual assault, like other kinds of traumatic experiences, has a powerful effect on memory -- sometimes in unpredictable ways.

This post reviews a few critical questions researchers in this field have sought to answer:

  1. How well do rape victims remember the details of their sexual assaults? 
  2. Why exactly does a trauma such as rape affect memory?
  3. What happens to those memories in the long term?
  4. What is happening in the brain that can make those memories unstable?
  5. What do these effects on memory mean for criminal investigations?
  6. How often does it turn out that the reports of rape are false?
1) How well do victims remember the details of sexual assaults?

Experts say rape exacts a toll on a victim's memory similar to other traumas -- from other violent crimes to car wrecks to warfare. People who endure these traumatic experiences often are unable to remember what happened to them accurately.

"We have a societal expectation that both the victim of a major crime and any witnesses to that crime ought to be able to remember with perfect clarity exactly what happened," said Rebecca Campbell, a psychologist at Michigan State University who studies sexual assault. "It is not an expectation that has any scientific merit."

In a 1996 study, researchers interviewed by questionnaire slightly more than 1,000 women at medical centers and 2,142 women at universities. The women were asked if they had been raped and to describe it, and if they had not suffered a sexual assault to describe another "intense life experience," marking whether it was positive or negative.

The researchers then conducted a statistical analysis of the responses and found that the results contradicted the widely held view that a major event that arouses strong emotions would be clearly remembered, since "the neural mechanisms underlying emotional memory suggest that any event that evokes intense arousal, positive or negative, could result in vivid and persistent memories."

To the contrary, they found that rape did not.

The rape memories reconstructed for the purpose of responding to the survey . . . were rated as less clear and vivid, less visually detailed, less likely to occur in a meaningful order, less well-remembered, less talked about, and less frequently recalled either voluntarily or involuntarily; with less sensory components including sound, smell, touch, and taste. . . .  Memories of events that were unexpected and highly negative both in their emotional valence and in their consequences were differentiated from memories of pleasant life events.

2) How exactly does a trauma such as rape affect memory?

There may be a number of reasons rape victims don't always remember the details of an assault.

One, according to experts, is that the body may focus on the direct source of a threat rather than contextual details, such as the time and place, that could later complete the picture of an attack. "Everything around trauma basically comes down to the biological drive," said Elana Newman, a psychologist at the University of Tulsa.

No readily available studies have looked at this in the context of sexual assault specifically. In one study, unsuspecting witnesses to a fictional crime saw only the criminal's weapon and were unable to correctly identify his face. Subjects in a famous 1978 study were asked to look at images of a traffic accident. Many of them couldn't remember whether a sign said "stop" or "yield" and would remember one or the other depending on what they were told about the accident afterward.

The stress hormone cortisol, in particular, can affect the parts of the brain responsible for recording new information. People, for instance, will do worse on tests of memory after taking cortisol, depending on the dose.

A 1999 study looked at 29 people in serious motor vehicle accidents within a week or two of the trauma. Fourteen of the participants showed signs of acute stress disorder in the days following the accident -- a precursor to post-traumatic stress disorder -- while 15 were more readily coping. Researchers asked each person to give a detailed account of what happened.

Those participants showing signs of acute stress used more than 1,300 words to describe the accident. But those without acute stress spoke in a concise 500 words. The lengthier accounts did not reflect greater detail but greater "disorganization" and "disassociation."

3) What happens to these memories in the long term? 

For some people, the immediate effects of trauma on the brain don't go away, and they develop PTSD.

About 1 in 3 victims of rape develops PTSD at some point, compared with about 1 in 20 people who have never been victims of a crime, according to the National Violence Against Women Prevention Research Center at Medical University of South Carolina.

Levels of depression are also much higher, with 30 percent of rape victims suffering from the disorder at one point in their lives, compared with 10 percent of non-victims. A third of rape victims also said they had contemplated suicide, compared with 8 percent of non-victims.

Experts say these effects on rape victims' mental health may be worsened by legal and medical systems that, as one study put it, "exacerbate victims' distress." Victims undergo invasive examinations and receive what they have told researchers feels like "cold, impersonal, and detached" treatment.

How a victim of rape remembers the assault can change with time as the mind works to organize its memories.

In one 1995 study, researchers examined victims of rape with PTSD who sat for 90-minute sessions with therapists. Over the course of nine sessions, the researchers found not only that PTSD rates declined but narratives of the trauma also "tended to become longer, perhaps reflecting the victims’ increased ability or willingness to engage in the processing of the trauma as anxiety decreases over the course of treatment," the researchers wrote.

However, in this particular study, the longer discussion was the result of patients talking more freely about their emotional response to the assault, rather than the "actions and dialogue."

But some experts say they believe that with the passage of time, memories often become more coherent and elaborate. "They have time to sit down, really go through that desk, find all of the Post-It notes and put them in order," Campbell said, comparing the mind to an office.

For some patients, the process makes the memory more accurate. But for others, people may be eliminating old memories and inventing new ones, with the hope of creating order of a chaotic event. "It's with an intent to make sense of what happens to you," Campbell said.

PTSD also affects memories that aren't related to the traumatic event itself. One 1998 study found that a third of rape victims with PTSD had trouble remembering words from a list, compared with 5 percent of the control group. Others with PTSD have demonstrated similar symptoms -- including veterans, war refugees and Holocaust survivors.

4) What is happening in the brain that can make those memories unstable?

One explanation is that PTSD damages the brain's recording device, a structure called the hippocampus.

On average, a person with PTSD has a hippocampus that is about 7 percent smaller than a healthy person's. It's possible that people born with a smaller hippocampus might be predisposed toward PTSD, but researchers say it's also possible that the hippocampus atrophies as a result of trauma. As a 1995 study put it, "Extreme stress results in increased release of glucocorticoids, excitatory amino acids, serotonin, and other neurotransmitters and neuropeptides that could be associated with damage to the hippocampus."

Here's a chart from that study, showing how well Vietnam veterans with different-size hippocampuses fared on tests of memory. Participants with a smaller hippocampus found it much harder to complete basic short-term-memory tests.

Am J Psychiatry
Am J Psychiatry
5) What do these effects on memory mean for criminal investigations?

The typical fact-based approach used by law enforcement during interviews is unlikely to work with a victim of sexual assault, experts say.

"If you go in with, 'Who? What? When? Where? Why?' you're not going to get much, because that's not how memory is organized," Campbell said. Instead, she said, psychologists, doctors and law enforcement will get more-reliable information if they allow victims to tell their stories in a freewheeling way, starting with the things they remember most clearly -- not with the things that happened first.

The advice contrasts with the way police are trained, which is to make establishing the facts a priority and to look for discrepancies as an indicator that a subject might be untrustworthy.

"In theory, I would say that someone who has been raped is going to stick quite rigidly to the account that they give," one British police officer told researchers in a survey. "Those that have made a false allegation, the story may well change, and sometimes they might come out and say things that you know couldn't be possible."

In a recent study of the Los Angeles Police Department, officers explained to researchers how the police handled people whom they believed were lying about having been raped. The goal was to "have them write it down; get them caught in discrepancies and have them tell the story left, right and center," one officer said.

As a result, police interviews can be counterproductive and harmful. Research suggests that victims of rape who feel they were incoherent in talking with police are less likely to continue with a criminal investigation. One of Campbell's studies found that if law enforcement or medical personnel received victims' stories with skepticism, they were more likely to develop PTSD.

The chemicals the body triggers in an effort to neutralize the pain of any traumatic event can also interfere with police investigations. Many people who have experienced trauma can recount what happened with a lack of emotion that causes others to doubt their version of events.

"When a victim of any major trauma is reporting to the police or to friends and family, and [the victim is] not a reactive hot mess, they think they're lying," Campbell said. "They see this person who is just totally flat, who is describing absolutely horrific things."

A group of psychologists at the University of Oslo confirmed that this can be a problem.

They filmed actresses giving scripted statements about a fictional rape with varying levels of emotion and then showed the tapes to several dozen police officers. The officers found the more emotional statements more credible.

6) How often does it turn out that reports of rape are false?

Researchers have struggled to determine the percentage of sexual allegations that are false but say the evidence suggests that demonstrably false allegations make up less than 10 percent of cases.

Much of the research into false allegations examines police cases. A 2010 peer-reviewed study published in the journal Violence Against Women reviews the scholarship to date, while assessing the flaws in existing studies.

The authors estimate the prevalence of false allegations of rape is 2 to 10 percent of cases reported to police.

The researchers also examined 136 rape cases at a major university in the northeast that had been filed between 1998 and 2007. The process took about two years, said lead author David Lisak. They classified complaints as false if there was "a thorough investigation" that resulted in evidence showing the assault never occurred -- such as video evidence.

Of the 136 cases on that college campus, eight were deemed false, or a rate of 5.9 percent.

False allegations differ from unfounded reports. The latter category also includes unsubstantiated cases in which law enforcement decides there isn't enough evidence to support the allegation and move ahead, perhaps because there is no physical evidence, or the victim was intoxicated and isn't able to precisely recall what happened. A rape still could have happened.

In the study of the Los Angeles police, researchers reviewed a random sample of 401 cases from 2008, examining case files and department detectives. They estimated the false-report rate was 4.5 percent.

It's also worth noting that cases reported to police represent only a fraction of the cases nationwide. A massive survey conducted by the Centers for Disease Control and Prevention has estimated that nearly 1 in 5 adult American women have been raped. Many of those women have been assaulted multiple times.

"However they end up being classified, a lot of these reports are never brought to court or never prosecuted, simply because there is a long-standing reluctance in the criminal justice system to take these cases," said Lisak, a clinical psychologist who retired from the University of Massachusetts. Rape cases are "labor intensive, difficult, not easy to win -- and for a whole host of reasons."