You Know More Than You Might Recall

July 28, 2005 — -- If you were asked to give your mother's name, your birthday or the steps to make a peanut butter and jelly sandwich you could rattle off these pieces of information from memory. But you'd be hard-pressed to explain exactly how you mastered the art of driving a car.

While memorized facts belong to the realm of conscious memory, skills like driving a car are governed by an unconscious kind of memory, sometimes called habit or intuition.

Researchers like Larry Squire of the University of California, San Diego are trying to understand just how it is we seem to learn things without remembering them.

Animals primarily make use of this unconscious memory, but "we [humans] have an overwhelming tendency to memorize everything when we're performing tasks," Squire said. For this reason, it's been hard to tease out just how much unconscious learning humans are capable of.

So Squire decided to work with a group of patients with damage to a region of their brain known as the hippocampus. The damage prevents these patients from forming new, conscious memories. Like the main character in the film "Memento," these patients can't remember any new information they take in after their brain injury.

Squire took 16 small pieces of metal or broken bits of toys and wrote the word "correct" on the bottoms of half of the objects. He used these "junk" objects so that they couldn't easily be associated with a word or a function. The patients were then presented with a pair of objects, one correct and one incorrect, and asked to choose the correct one.

For most people, a couple rounds of the game would be enough for them to memorize which of these odds and ends were "correct." But these patients played this game with researchers twice a week for more than seven months. And each time they came in to the testing center they had no idea what the game would be, or what the rules were.

After about four weeks, something unusual began to happen. The patients would come in and, without prompting, begin to pick up the object, looking underneath them. When asked what he was doing, one of the patients responded, "That's just habit, I think. It's just, what's underneath?"

By the 18th week, the patients were picking the correct objects about 80 percent of the time. They were learning the correct objects, without actually remembering them.

"How am I doing this?" one of the subjects asked, after picking up another object with "correct" written on the bottom.

"It just seems to be automatic," said another patient. "My mind just seemed to tell me, 'just pick it up, it's the right one!' "

"There are these powerful unconscious learning systems," Squire explained. This ability to perform well a task you can't remember shows that some systems in our brain take in information without our notice.

But this kind of habit learning is rather inflexible. For example, when the patients were presented the object all at once, as opposed to in sets of two, they were no longer able to pick out the right ones.

It's like tennis, Squire explained. Just because you're a good tennis player, doesn't mean you'll be good at squash. Though the tasks are similar, our unconscious memory only works under very specific circumstances.

"One of the mysteries of human nature is that there is so much going on unconsciously," Squire said. Everything we do, from washing our hands before a meal to saying please and thank you builds these unconscious memories in our brains. "We're learning from the world all the time," Squire said. These observations and repeated behaviors form our disposition, without us even knowing it.

Squire's research will be published in this week's issue of the journal Nature.