How the Brain Makes Quick Decisions

Feb. 19, 2009 — -- It's the last set at Wimbledon and Serena Williams needs a little magic to take the match. Her opponent makes an amazing shot, but Williams somehow knows where the ball is going, and she's there. How could she have read her opponent's mind?

She didn't. But she may have been helped by a kind of human memory that scientists have been struggling to understand. Using her "implicit" memory, a short-term memory that people are not consciously aware they are using, Williams could have recognized her opponent's moves just before she hit that amazing shot, because she had seen the same moves a few minutes earlier when her opponent made a similar shot.

Of course, that's not the only thing that got Williams to the finals. Athleticism, conditioning, hard work and talent were the main reasons. But she had something else at work, and the rest of us use it all the time even if we don't know it. Sometimes, when we have to make a quick decision, we may think we're guessing, but we may be basing that "gut response" on real information, collected a few minutes earlier.

That's the implication of long-term research at Northwestern University in Evanston, Ill., by psychology professor Ken Paller and Joel L. Voss, who is now at the Beckman Institute, an interdisciplinary-research facility affiliated with the University of Illinois at Urbana-Champaign. Their research did not specifically involve athletics, but the results are consistent with work by other researchers who are studying how top athletes can make split-second decisions with very little information. How does a batter hit a fastball when he has to start swinging the bat before the ball even leaves the pitcher's hand? He relies on visual cues, even if he doesn't know it.

"Athletes learn to predict based on very little information," Paller said in a telephone interview.

In their most recent research, published in the journal Nature Neuroscience, Paller and Voss reveal a surprising discovery. Participants in that study were purposefully distracted while trying to quickly memorize visual patterns with their implicit memory and, quite surprisingly, did better when distracted than when they weren't.

Not Just a Gut Reaction

"That's a very striking part of the testing and a little perplexing," Paller said. "We know that when you pay less attention, that seriously disrupts normal memory," but a little distraction helped short term memory, at least in this experiment.

A dozen students were recruited for the project. That's a small sample, but the results are consistent with earlier experiments involving far more participants, and all of the experiments yielded similar results: When forced to make a quick decision, we may be relying on real data, not just a gut reaction.

Paller and Voss took their research a step further in this experiment. They plastered the heads of the participants with sensors that recorded brain waves. "The different types of memory have a different electrical pattern that we record," Paller said.

Short-term memory is also stored in a different area of the brain than long-term memory. The patterns produced during the experiment revealed that short-term memory was indeed the key to success in recognizing images the participants had seen a few minutes earlier.

"Our study is new in a few ways," he added. "We showed that implicit [short-term] memory can actually help you when recognition memory is being tested. People weren't sure it helped you pick which things you've seen before, so we were able to show that the unconscious type of memory can help."

Participants sat in front of a computer monitor as multicolored patterns flashed on the screen. Later, they were shown two images and asked to immediately identify which of the two images they had seen before, even if they had to guess. But it turned out that even when they thought they were guessing, they got the right answer most of the time, so they were doing more than guessing. They were also drawing on their short term, unconscious memory.

During parts of the experiment, participants were distracted from their visual assignment when they were ordered to remember a spoken number because they would have to identify it later. Distractions are known to impair the capture of long-term memories. We have to focus to remember well.

Help With Amnesia Patients

But that's when the surprise came.

"Remarkably, people were more accurate in selecting the image they had seen before" when asked to pick which of two images they had seen, Paller said. "They also were more accurate when they claimed to be guessing than when they registered some familiarity with the image."

It's not clear why the distraction helped instead of hindered. Paller suspects that one reason the distractions didn't hurt is that they involved the auditory system, not the visual system used in the recognition of colorful patterns. But that doesn't explain why people knew the answer when they thought they were guessing.

The real-world implications for this research are also unclear, at least at this time. Paller thinks it will be helpful in his long-term study of amnesia patients who retain some short-term memory but not long term. But will this really help Williams capture another trophy?

Maybe, if we understand it better, and that's the point of this kind of basic research. The work shows we have a tool we didn't know we had, a knowledge-based short-term memory that can be called upon for split-second decisions. That's a lot better than a guess.