Harvard Medicine

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What Meets the Eye

Our ability to take in visuals may reveal only a small portion of what is really there.

© Dan Tero<br/>iStockphoto.com Vision, wrote Jonathan Swift, is the art of seeing the invisible. In truth, however, we may not even notice the obvious, says Jeremy Wolfe, HMS professor of ophthalmology and head of Brigham and Women’s Hospital’s Visual Attention Lab. Together with Todd Horowitz and other colleagues, Wolfe is identifying the ways in which we search for objects and detect changes in what we see—research that has real-world implications for fields as diverse as baggage screening and radiology. The researchers’ conclusion: We often miss what’s right in front of our eyes. “We believe we’re viewing the whole world,” explains Wolfe. “But we’re only processing a small part of it at any one time.”

We perform visual searches every day, whether rifling through a drawer for car keys or assembling a jigsaw puzzle. But some searches—for a gun in carry-on baggage or a tumor on an MRI scan—are more crucial than others. Studies by Wolfe, Horowitz, and others suggest that the less common an object is, the harder it is to spot it when it appears. “Targets like guns and tumors are relatively rare,” says Horowitz, an HMS assistant professor of ophthalmology. “So we’re less likely to notice them when they do show up.”

Inspired by findings from their laboratory research, in which volunteers were asked to locate unique letters or symbols on a computer screen—a single letter T in a field of Ls, for example—Wolfe and his colleagues have expanded their experiments. In one recent study, they asked participants to search for weapons in computer-simulated baggage. The participants were told the rough likelihood that a weapon would be present and were rated on both the time it took them to identify the object and their accuracy. When told that weapons were rare, participants dismissed luggage more quickly and failed to locate more of the weapons that were present. When told that the weapons were common, they dismissed luggage more slowly and reported seeing weapons that were not present.

“This phenomenon is likely ancient and widespread rather than a product of modern civilization,” Wolfe says. “If a prehistoric ancestor was examining a bush that almost always yielded food, for example, she probably kept searching for a long time.”

The vision laboratory’s findings have practical applications for training airport security personnel, Wolfe adds. He is planning to conduct similar investigations working with radiologists, who worry about misses as well as the consequences of false-positive reports of tumors. The research may also translate to other types of visual searchers, from Coast Guard officers looking for overturned boats to government employees interpreting spy satellite images.


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