Babies tune in to size in social hierarchies

"From my evolutionary perspective, this is an aspect of human social organization that is fundamentally important. And if it's fundamentally important, than very young children should have some predilection to be tuned into these cues from very early on," said Patricia Hawley, a professor of psychology at the University of Kansas who was not involved in the study and praised it for the way researchers systematically ruled out other possible explanations for the babies' behavior.

Since infants who are still learning their first words can't describe their thoughts, Thomsen, working with Harvard psychology professor Susan Carey, used a "looking time" experiment. Such experiments are well-established in developmental psychology, taking advantage of the fact that even young babies can formulate expectations about situations. If a scenario violates that prediction, they will stare for much longer at a screen, as if they are trying to understand what went wrong.

In the experiment, babies from 8 to 16 months old sat on a parent's lap and watched animations. A big blue block with an eye and mouth bounced from left to right. Then, a similar but smaller green block bounded in the opposite direction. Then, researchers showed the two blocks were in conflict: both started at opposite corners, and when they met in the center, they bumped into each other and reversed direction.

Two different scenarios were shown. In one, the blocks bounded toward one another, bumped, and then the small green block bowed and moved out of the way so the big blue block could continue on its way. In another, the large blue block prostrated itself in front of the small green one before moving out of the way so the little block could continue.

Researchers froze the screen after each scenario for one minute, and found that babies consistently stared longer at the unexpected scenario than the expected one -- for 20 seconds on average, instead of 12. The difference was noted in 10-month-olds, but not in the 8-month-olds.

Such experiments may sound incredibly simple, but researchers tested 144 babies and painstakingly designed a number of experiments to ensure their interpretation was correct. They determined that infants weren't staring longer at the animation because when the bigger block fell there was more mass in motion, or because babies expected that small creatures were more likely to fall down.

Such experimental techniques have fostered burgeoning interest in exploring the social abilites of babies. In 2007, J. Kiley Hamlin, now an assistant professor of psychology at the University of British Columbia, showed that infants as young as six months old prefer characters that are helpful over ones that hinder. Her lab is presently working on other social questions, such as how babies make character judgments about who deserves what.

"The idea I'm starting to come to myself is that these things are maybe fundamental to how a baby would interpret an interaction they did experience," Hamlin said. "We're really finding amazing competence across the board ... The more we test them, the more they surprise us."

For Thomsen, these questions about social hierarchies extend into school and even into adulthood. As part of her doctoral thesis, she found that adults' preference for a hierarchical pyramid symbol predicted racist and ethnocentric views. Now, she is finding that preschoolers also intuit hierarchy from looking at the abstract symbols, guessing that the top part of the pyramid represents the strongest, oldest, or most popular.

Preschoolers' preference for the overlapping icon is turning out to be a predictor of how well they share when given stickers, and how secure they feel about friendships.

"The more we understand about how social hierarchy and dominance hierarchies work and how
we recognize them and how we manipulate them -- that should ultimately also make us able to intervene and shape them in ways that are less harmful," Thomsen said.

E-mail Carolyn Y. Johnson.