Racy and Gory Images Cause Temporary Blindness

Here's the scene: You've seen a flash of nudity on the telly just as your sweetie walks in the room, and you don't even notice the love of your life.

It's a bad scene, but hey, you're innocent. You've just been hit by something researchers call "emotion-induced blindness."

It's not a serious disease, unless your sweetie has a powerful right hook, but new research shows that instantly after seeing an erotic image, or a violent scene, we wouldn't notice a building lying on its side. Literally.

Psychologists at Vanderbilt and Yale universities have been studying the effect that highly emotional images have on our perception of the world around us. And they've found convincing evidence that the human brain just can't process information that it receives immediately after seeing a violent or erotic scene.

We're talking real short term here, around a fifth to a half a second, but given the speed of today's society, that may be enough to worry about. A fast-moving vehicle, for example, can travel a significant distance in that brief span of time.

Split-Second Distraction

Psychologists David Zald of Vanderbilt, and Steven Most, Marvin Chun and David Widders of Yale, started by looking at the effect of gory images, like a fatal traffic accident, on the brain's ability to process subsequent information.

They programmed a computer to show a series of images in rapid succession. Each image was shown for precisely 100 milliseconds (one-10th of a second.) Most of the images were neutral, thus requiring no or very little emotional response, but every now and then they tossed in a gory scene.

The computer also flashed pictures of a building lying on its side, and participants in the project were told to indicate with an arrow key which way the building was lying.

That's a pretty easy task, but if the building came a fraction of a second after a gory image, the participants missed it entirely.

"They didn't see it at all," says Zald.

The biggest effect came if the building followed the gory scene by 200 milliseconds, or one-fifth of a second.

"You can see lesser effects out to maybe half a second," Zald adds, "but it's pretty much gone after that."

Blinded by Beauty

That left the researchers with a basic question. Was it the negative nature of the image that caused the temporary "blindness," or would an arousing scene do the same thing?

To find out, they ran the same experiments over again, this time using erotic material just before the toppled building.

And they got the same result.

"We always see it," Zald says.

If the participants had been slow to respond, it would simply mean they had been distracted by the emotional images, and soon recovered. But the fact that they never even saw the image of the building lying on its side is very significant.

"That's what's striking," Zald says.

Cautious Persons More Susceptible

It's also significant, the researchers report in the August issue of Psychonomic Bulletin and Review, that there were personal differences among the participants in their ability to see the image showing the building lying on its side. (The lead author of that report is Yale's Most.). Some participants were more susceptible to the emotional images than others.

"We've seen the most clear-cut differences in terms of a personality dimension we call 'harm avoidance,' " Zald says.

Participants in the research were tested to see if they rank high in "harm avoidance," meaning they are cautious and want to avoid situations in which they could be hurt, or if they rank low, meaning they are more carefree and willing to take a risk. So far more than 100 persons have been tested, and the researchers say the results are clear.

The more cautious participants, those who wanted the most to avoid personal harm, suffered more from temporary blindness than those who were more willing to take a chance.

The purpose of the research, of course, is to delve into the workings of the human brain. But there's a practical side to it as well.

Our response to highly emotional stimuli could be dangerous.

"If you take a basic evolutionary type perspective, something that is violent or gory could be a risk to us, and things that are erotic have the potential for procreation," Zald says. So we need to pay attention to both of those, but that imposes some risks.

"It's a trade-off," Zald says. "It's ensuring that we pay attention to this information, but it comes at our cost of failing to see other relevant information.

"In that sort of cost benefit analysis, one suspects that in the past it was beneficial. At our high-paced speed today, it's possible it becomes detrimental."

A terrible traffic accident, for example, may leave us unable to see a child darting into the road ahead of us.

Lee Dye's column appears weekly on ABCNEWS.com. A former science writer for the Los Angeles Times, he now lives in Juneau, Alaska.