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By the end of the first year, infants can both express and perceive anger, most researchers agree. What they express is not identical to adult anger, and what they perceive lacks the nuances that come with language and experience. But by their first birthday, they have taken the first steps down a path that will eventually lead to adult anger, studies suggest.

Go back much earlier, though, and the consensus on what infants can feel, express and perceive falls apart. Some researchers say that anger appears within the first few months of life, while others say it takes until the very end of the first year for the individual components of anger--such as subjective experience and facial expression--to come together. As University of California, San Francisco psychologist Paul Ekman, PhD, notes, whether infants can feel, express or perceive anger are empirical questions for which the data are simply not yet all there.

Do infants experience anger?

DePaul University psychologist Linda Camras, PhD, is one of those who believe that the use of the term "angry" to describe infants before the age of six months can be misleading.

Infants often use "angry" facial expressions in situations that aren't at all similar to those that make adults angry, she says, so using general terms such as "distress" to describe their emotions is more appropriate than using "anger."

"Up until toward the end of the first year, it really makes more sense to say that babies are upset or unhappy, rather than that they're specifically angry," says Camras. A term like "upset" indicates that the infant is experiencing a negative emotion, she explains; "anger" assumes, perhaps incorrectly, that the infant's emotions are as well-differentiated as those of adults.

Other researchers believe that infants' emotions are, if not entirely as well-differentiated as those of adults, then at least differentiated enough that it is appropriate to use "anger" and other descriptors of adult emotions.

One of them is University of Delaware psychologist Carroll Izard, PhD, an expert on facial expressions and the designer of a widely used system for codifying facial expressions ("The maximally discriminative facial movement coding system," University of Delaware, Information Technologies and University Media Services, 1989).

Izard believes that facial expressions of anger appear within the first six months of life, perhaps as early as three months, and that facial expressions can reliably indicate the presence of an emotion, even in infants.

Nonetheless, there are significant cognitive differences between anger in infants and anger in adults, says Izard. Infants lack the language that adults use to understand and express their anger, as well as the personal experiences and cultural values that shape it. So their internal experience of anger is undoubtedly very different from that of adults or even children a few years older.

"When adults think of anger, they immediately think of things that make them angry--there's a lot of cognitive context," says Izard. "For the infant, there may be no cognitive context. So we have to be careful to distinguish what we're talking about."

Do infants express anger?

Infants, like adults, furrow their brows when angry, says Izard, but unlike adults they don't tend to compress their lips. Instead, their mouths take on a square-like, angular shape. When infants are sad, in contrast, they tend to raise the inner corners of the brow and turn down the corners of their mouths.

However, infants in different cultures may express their emotions differently, says Camras, although the evidence remains inconclusive.

For example, Camras and her collaborators have found that Chinese infants appear to be less emotionally reactive than Japanese and American infants. In studies published in Emotion (Vol. 2, No. 2) and Developmental Psychology (Vol. 34, No. 4), Camras and her collaborators reported that Chinese infants are slower to smile and slower to cry, and that it is harder for adult observers to tell when they are surprised.

The cause of those differences is unclear. Perhaps it has something to do with the traditional emphasis on emotional restraint in China, versus the emphasis on self-expression in the United States, says Camras.

"We're not quite sure which of the parents, whether American or Chinese, are acting in a way that shifts the baby," she explains. "Probably both sets of parents are."

Can infants perceive anger in adults?

A recent study by Long Island Univer-sity psychologist Diane Montague, PhD, and Rutgers University psychologist Arlene Walker-Andrews, PhD, suggests that infants as young as 4 months old can distinguish between anger, sadness and fear in adults.

Montague and Walker-Andrews used a "peekaboo" game in which an adult researcher modeled a series of different facial expressions. The researchers found that the amount of time the infants spent looking at the expressions depended on the emotion shown. With sadness, the infants looked less and less over the course of the experiment; with anger, they looked more.

The study, published in Developmental Psychology (Vol. 37, No. 6), doesn't prove that infants understand the meaning of the expressions, but it does suggest that their behavior is differentially shaped by them.

That, together with other research, suggests that positive emotional interactions between infants and adults could have a long-term impact on the infants' development, says Izard.

"There's good research that shows that playing emotion-expression games with infants has a lot of good long-term effects, and that it makes for a healthier, more adaptive child in later life," he says.

Can adults perceive anger in infants?

Some research suggests that adults can distinguish among infant emotions, but other research indicates that the performance of adults depends to a great extent on how the experiment is conducted.

In one study, published in Developmental Psychology (Vol. 28, No. 6), New York University psychologist Harriet Oster, PhD, and her collaborators reported that adults prefer to describe infants' emotions using general terms, such as "distress." They only use more specific terms, such as "anger," "fear" or "sadness" when those are the only word choices available to them.

Another study by Camras and her collaborators, published in Emotion (Vol. 2, No. 2), suggests that infants rarely make facial expressions of surprise when they see an unexpected event. Furthermore, adults tend to use other signals--such as bodily stilling and facial sobering--to judge when an infant has seen such an event.

These studies and others suggest that perceiving emotion in infants is a holistic process, one that depends not only on facial expressions, but also on gestures, posture, situational cues and--perhaps most importantly--the perceiver's ideas about the capabilities of infants.