Seeing is believing when it comes to emotions. We smile, we gasp, we yawn when we see others do the same—a phenomenon called emotional contagion.

A new study published last week in Proceedings of the National Academy of Sciences finds that emotional contagion occurs even if the "seeing" step is bypassed. The blind patients in the study could not consciously see images of the faces of happy or fearful people that they were shown. Although their eyes and optic nerves were functional, the region of their brains involved in visual processing had been damaged. Instead, other parts of the brain took over, allowing the subjects to still respond normally with their own happy or scared facial expressions. These patients also made the appropriate happy or fearful face in response to emotions that were communicated through bodily expressions, suggesting that blind empathy can happen even without a facial template to imitate.

"We're actually infected by the emotions of others. [This study shows] this phenomenon can be carried out in the absence of visual awareness," says Marco Tamietto, a neuroscience researcher at Tilburg University in the Netherlands and lead author of the study. "We can say that emotional contagion cannot be reduced to a simple mimicry."

To tease apart the mechanism underlying emotional contagion, Tamietto and his colleagues took advantage of what is known in neuroscience as "blindsight". Starting a few decades ago, researchers found that patients who have damage to the part of the brain called the visual cortex, which processes visual information, retain a sort of sixth sense of sight. Although they are not aware of information in their visual fields, that input, whether it is a color, shape or facial expression, is still entering their eyes and being sent to and processed by other regions of their brains. One area known to receive visual information independently of the visual cortex is the amygdala, the brain's emotional control center.

"With these patients, they feel they're blind…. If you flash them [an image of] something, they claim they don't see anything, but they guess reliably above chance" what the image is, says Marco Iacoboni, a professor of psychiatry at the University of California, Los Angeles, (U.C.L.A.) and author of the book Mirroring People. Iacoboni was not involved in the recent PNAS study.

Tamietto and his colleagues studied two adult patients whose visual cortices had been damaged—one because of surgical removal at age 33, the other by a traumatic brain injury at age seven. As a result, each was blind in either the right or left side of the visual field. Even though both of their eyes was sending information from both sides of the visual field to the visual cortex, damage to the left side of the visual cortex, for example, made the patient effectively blind in the right side of the visual field.

The authors showed them pictures of faces of people with happy or fearful expressions on either the right or left side of a computer screen while the patients kept their eyes fixed on the center of the screen, and measured the spontaneous change in their facial muscles via electromyography (EMG). The patients responded by smiling at happy faces and frowning at faces showing fright that were shown to both their sighted and blind visual fields.

As Tamietto says, these facial responses could still be the result of the patients automatically mimicking the expressions that they see, even if they are seeing them on an unconscious level. The alternative is that the expressions on the screen are actually eliciting the same mood in the subjects. To distinguish between these two possibilities, Tamietto and his colleagues showed the patients images of happy or fearful body postures that would be emotional cues but not provide the information needed for facial imitation. The response was the same: In both visual fields, the patients responded by smiling at happy bodies and frowning at fearful bodily postures.

These results suggest, "you are really into the same emotional mood, so you are not simply imitating but you are unknowingly driven to the same emotional mood," Tamietto says.

Iacoboni at U.C.L.A., however, is not convinced that mimicry is not involved. Because the study did not look at muscle movement in the body, only the face, it remains possible that the patients adjusted their bodily positions to imitate those on the screen, and then that emotion spread to their faces. One way to examine the role of imitation, he says, would be to look if the parts of the brain where there are mirror neurons are active in these studies.

In addition to suggesting that we can empathize with others' emotions on an unconscious level, the authors also noticed that this reaction was faster than the one that involved the visual cortex. Whereas patients took about 1.2 seconds to respond to images
on their functional side, they reacted in 0.9 second to images in the blind visual field, according to the EMG recordings.

When the visual cortex is working, most of the visual information is routed through this part of the brain, says Alan Pegna, director of the Laboratory of Experimental Neuropsychology at Geneva University Hospital in Switzerland who was not involved in the current study. He has studied patients with blindsight, or the type of seeing that does not involve the visual cortex. "The idea is the information is reaching the amygdala in a kind of direct, quick and dirty route," he says. When the visual cortex is out of commission, more of the visual information could be fast-tracked to the reflexive regions of the brain.

Tamietto says the unconscious route could also process visual information for other basic human emotions, including anger and sadness. "Those were events relevant for survival of our ancestors that required a rapid reaction to the environment mediated by phylogenetically ancient pathways that bypass the visual cortex," he says. But lest we forget the importance of the visual cortex, he adds: "To really understand the intentions of others, we have to be conscious." For that, we need the awareness that arises from those perceptions derived from the visual cortex.