Researchers Take a Closer Look at Vision

Psychologists know that our brains constantly make decisions about what to look at. Neuroscientists like to study how the human brain juggles the information. New information has recently emerged.

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SCOTT SIMON, host:

Our brains are always making decisions about what to look at. Now here in the studio, I have to look at the script I'm reading, look at the microphone, I also have to keep an eye on the clock and another on our director, Sarah Bey--oh, wait, it's Brendan Banaszak today. Neuroscientists have recently made some interesting discoveries about what we see and what we miss. NPR's Joe Palca has more on the story.

JOE PALCA reporting:

If I say `Pay attention,' that command seems easy enough to understand. But a psychologist like David Melcher of Oxford Brookes University in England will tell you that there's paying attention and then there's paying attention.

Mr. DAVID MELCHER (Oxford Brookes University): If you're listening to the radio when driving, hopefully you're not paying too much attention to NPR, but if you were, you might not notice that someone was coming in from the left and might pull out in front of you. And it's critical that part of your brain is very interested in the possibility that a car might pull out in front of you without you having to think about it all the time.

PALCA: Melcher has been studying how the brain processes information we see but aren't conscious of seeing. In a series of experiments described in the journal Neuron, Melcher has shown that what we look for in our surroundings influences what we only catch out of the corner of our eye.

Mr. MELCHER: So if you start to pay very close attention to motion and all of a sudden your brain is highly sensitized to motion all around you, if you start to pay attention to something red, then all of a sudden you notice all of the red things around you.

PALCA: This finding is at odds with how scientists used to think attention worked. Geoffrey Boynton is a neuroscientist at the Salk Institute in La Jolla.

Mr. GEOFFREY BOYNTON (Salk Institute): The model we had behind spatial attention was that it was coded to act like a spotlight, where as you move your attention around a visual field without moving your eyes, it's sort of like enhancing the brightness or contrast of the part of the world that you're attending to at the expense of the others.

PALCA: But Boynton says it now appears things are more complicated than that. He says that some of the light from that spotlight spreads out, giving an inkling of what's happening off to the side. And we can make conscious use of that unconscious information.

Mr. BOYNTON: Suppose you're looking at a shelf of books and you want to find a particular red book on the shelf. Well, if you've noticed, and if you do that, your eye will jump from one red book to another, completely ignoring all of the other books of different colors. And it makes sense that when red is the important color to you, the brain's response to all the red things is enhanced and that allows you to just simply jump from one red object to another and have all the other information filtered out.

PALCA: Boynton has begun to wonder if this ability to filter information breaks down in people with learning disabilities.

Mr. BOYNTON: Maybe something's gone wrong with this mechanism where your ability to ignore stimuli outside your focus of attention is not operating properly.

PALCA: Boynton is about to launch a study of people diagnosed with attention deficit disorder to see if their brains behave differently from people without the disorder.

A better understanding of how the brain pays attention could have implications for national security. Jeremy Wolfe of Harvard Medical School says even when we're trying really hard to pay attention we can miss things. He says our brains are not designed to pick out really rare events, and that could be a big problem for airport baggage screeners looking for bombs or weapons.

Mr. JEREMY WOLFE (Harvard Medical School): You're dealing with a situation where you have to do search after search after search and you're always saying, `No, it's not there, it's not there, it's not there.' You're looking for this very rare target, and it turns out that you are ill-suited to doing that.

PALCA: Wolfe has done experiments in the lab where subjects do poorly at finding rare objects. He says essentially it's a case of if you don't see something often, you don't often see it. Just another example that paying attention isn't as simple as it sounds. Joe Palca, NPR News, Washington.

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