Our memory is like an ear of corn. At least, that’s what Valerie Reyna was taught in graduate school.

Its Forrest Gumpish feel notwithstanding, the metaphor seemed scientifically sound. After all, researchers had already concluded there are two distinct types of memory: Verbatim, which allows us to recall what specifically happened at any given moment, and gist, which enables us to put the event in context and give it meaning.

“We were taught you extracted the gist from the verbatim memory,” recalled Reyna, an experimental psychologist and former senior research adviser to the U.S. Department of Education. “It was like husking an ear of corn. You threw away the husk, which was the verbatim, and you kept the gist, which was the kernel of meaning.”

There it was: Neat. Simple. Agrarian.

And also, as Reyna discovered over decades of subsequent research, wrong.

After conducting numerous studies with her partner, psychologist Charles Brainerd, Reyna concluded that verbatim and gist memory are separate, parallel systems. So separate, in fact, that “there is some evidence” they occupy different sections of the brain.

Reyna and Brainerd’s hypothesis, which they call “fuzzy trace theory,” explains how we can “remember” things that never really happened.

When an event occurs, verbatim memory records an accurate representation. But even as it is doing so, gist memory begins processing the information and determining how it fits into our existing storehouse of knowledge. Verbatim memories generally die away within a day or two, leaving only the gist memory, which records the event as we interpreted it.

Under certain circumstances, this can produce a phenomenon Reyna and her colleagues refer to as “phantom recollection.” She calls this “a powerful form of false alarm” in which gist memory — designed to look for patterns and fill in perceived gaps —creates a vivid but illusory image in our mind.
Mental snapshots soon fade; what lingers are our impressions of an occurrence, which are shaped by the meanings we attach to it…

“We’re looking at a number of things, including the effect of emotion on memory — how emotion interacts with your interpretation of events,” Reyna said. “Does arousal interfere with your encoding of memory? Does it ‘stamp it in,’ as some of the neuroscience literature suggests? The effect might be more complex than that.”

One question that can’t be answered in the lab is why, in evolutionary terms, we would develop two separate memory systems. Reyna, who has given this considerable thought, noted that if all we had was our rapidly fading verbatim memory, “it would be very hard to function — especially in an oral culture. Cognition appears to be engineered around gist memory, which endures and is stable.”

Consider the case of one of our prehistoric ancestors who is attacked by a saber-toothed tiger but manages to escape before being eaten. Verbatim memory would tell him precisely where the altercation took place, exactly what the tiger looked like and what tree he climbed to get beyond the animal’s reach. Gist memory would tell him: “Tigers are dangerous. If I go walking in the forest after dark, I’d better bring my spear.”

The first would be interesting; the second, essential. As Reyna wryly noted, “You don’t have to count the stripes to know the tiger is bad.”

Tom Jacobs