Alcohol, even in moderate amounts, also tends to undermine the brain’s ability to encode and store sights, sounds and other details, particularly in a coherent sequence. The accounts of both women note the consumption of large amounts of alcohol; Dr. Blasey described Judge Kavanaugh and his friend as “stumbling drunk.” Ms. Ramirez, who alleges that he exposed himself to her during a college party, said she herself was inebriated and slurring her words at the time. These memories might be fragmented or “impaired,” said Jim Hopper, a psychologist and teaching associate at Harvard Medical School and a consultant on cases involving trauma and memory.

Retrieving such experiences from memory is an equally selective task and prone to error. In biological terms, recollection is a process of both revisiting and reassembly. Recalling an event draws on some of same areas of the brain that recorded it; in essence, to remember is to relive.

Every time the mind summons the encoded experience, it can add details, subtract others and even alter the tone and point of the story. That reassembly, in turn, is freshly stored again, so that the next time it comes to mind it contains those edits. Using memory changes memory, as cognitive scientists say. For a victim, often the only stable elements are emotions and the tunnel-vision details: the dress she wore, the hand over her mouth.

“My experience is that this is the way people recall traumatic experiences,” said Esther Deblinger, a psychologist and the co-director of the Child Abuse Research Education and Service Institute at Rowan University School of Osteopathic Medicine.

The reliability of those details depends in part on when they entered the narrative. “In this case the question is, when did the accuser attach Brett Kavanaugh’s name to the incident?” said Elizabeth Loftus, a professor in psychological sciences at the University of California, Irvine. “Was it right away or did it come much later, say, in therapy?”

That answer is unclear in Dr. Blasey’s case; all that’s known is that her husband recalled that she mentioned the name Kavanaugh when she described the incident in a couple’s therapy session in 2012. (The therapist’s notes don’t identify him.) In general, Dr. Loftus said, the earliest or first memory of an event is the more reliable one.