If you come across someone staring up at the sky, chances are you’d look up too… but not if that person’s eyes are closed.

This ScienCentral News video reports that infant researchers wanted to know if that’s too subtle a difference for 12-month-olds. They say the fact that it isn’t tells us a lot about child development.

Out of sight, out of mind

Swiss psychologist Jean Piaget came up with the term “object permanence” to describe the fact that young infants think an object ceases to exist when it is no longer in sight. In other words, take a ball away from a 3-month old and put it in the closet, and he’ll think that there is no more ball. Do the same thing to a 9 month old, and she will know to go into the closet for the ball if she wants it.

Child development is full of these subtle changes that we take for granted as adults. Another thing child psychologists are interested in teasing out is when children start to develop a “theory of mind”—or the ability to recognize that other people have their own thoughts, and to be able to infer what those thoughts might be.

To get an idea, Rechele Brooks, research associate at the University of Washington’s Center for Mind, Brain & Learning, looked at gaze following in 12-, 14-, and 18-month-olds. Previous studies showed that when an adult turns to look at something in a room, an infant will follow the adult’s gaze and look toward the object as well. But it was unclear whether the child was simply responding to the movement of the adult’s head or whether the infant knew to look where the adult was looking because they recognized that the adult had found something specific and interesting in the room.

Brooks felt that experimenting with eye contact would help tease out the difference. While playing with children at a table, she set up colorful toys on the left and right sides of the room. At certain points during the experiment, she turned to look at a toy, but sometimes did so with her eyes closed.

“And we were pleasantly surprised that our study broke new ground, because we were the first to show that that eye contact at twelve months matters to young children,” she says. “And it matters in a specific instance that we think is important.”

That is, children were unlikely to look at the toy if Brooks’s eyes were closed, but very likely to do so when her eyes were open. This rules out the notion that head movement in and of itself sort of drags infants’ attention to where someone else is looking. The fact that they know you are using your eyes to find something in the room is a clue that 12-month-olds recognize that you have distinct thoughts and ideas, and that these thoughts can be shared.

“Then sometimes they'll even point at it,” Brooks says. “And it's sort of as if to say, ‘Oh, it's over there! We're doing this together!’ And kids get really excited about doing things with another person. It’s a beginning, I think, of children beginning to understand that we share attention, that we're interested in things together.”

Beyond pointing, Brooks and her colleague, Andrew Meltzoff, also noted that children would tend to babble more when Brooks looked at the toy with open eyes.

“And it's that package of children's actions—where they point and talk and look—that really conveys that they’re beginning to understand that we're sort of having a conversation. That we're indeed having a social interaction,” Brooks says.

Understanding when these stages of development occur can help parents understand at what age they can expect their children to take in another person’s point of view. And it’s important in helping establish a baseline for what is normal in child development. Theory of mind is a concept that children with disorders like autism find hard to grasp, and the lack of acquiring this important building block of development—realizing the importance of eyes—may be an early indicator of a social disorder.

Brooks says she next hopes to do similar studies in even younger children, to see how early this behavior is present. Her work was published in the journal Developmental Psychology, and was funded by the National Institute of Child Health and Human Development, the Talaris Research Institute, and the Apex Foundation.