How much do infants know about the world in which they live? At what age do humans begin to develop an understanding of object permanence and of the reality that people act in response to different things around them? These are the kinds of questions Yuyan Luo, Assistant Professor in the Department of Psychological Sciences, seeks to answer. In addition to teaching cognition development courses—from infancy to toddler—she runs the Infant Cognition Lab, which tests psychological and biological knowledge development through a series of lab experiments. Now in its second year of operation, the lab conducts experiments with participants as young as two and one-half months old.
Most of Luo’s studies use the so-called “looking-time method,” which measures how long an infant looks at different events. Typically, two types of events are shown to the infant: one that is consistent with the type of knowledge being tested, and one that is inconsistent. “If babies do have that kind of knowledge, they will be surprised by the inconsistent event and look a long time,” Luo observes. For example, in one type of looking-time experiment, babies are shown a box floating in mid-air. If babies are intrigued by the floating box and watch it for a long period of time, “that means they know that something needs support in order to be stable, that it shouldn’t just float.” Luo is currently using this kind of task to compare “infants' responses to a floating box and a floating person. Eight-month-olds seem to know that people cannot float and thus find the floating person somehow aversive.”
Luo’s interest in studying infant cognition began in graduate school when she encountered a paper authored by her advisor, Dr. Renée Baillargeon, on the subject of object permanence—“knowing that objects move and exist continuously in time and space.” Jean Piaget, the famous Swiss psychologist, had previously claimed that the notion of object permanence could not be understood before the age of eight months. However, Baillargeon proved that when given the proper task infants as young as two or three months displayed an awareness of object permanence. The problem with Piaget’s method lay in his experimental procedure: he was using a two-step manual search task that required infants to lift a piece of cloth to find a toy underneath it. As Luo explains, “if you think more about this task, as adults we have to plan ahead. We have to understand this is a two-step action—we need to lift the piece of cloth, and then get the toy. Babies younger than eight months are not good at reaching for something, using their hands, or planning for this two-step action. They have trouble with that kind of task, which is why they cannot succeed in the search task.” Methods that employ looking-time studies, as used by Baillargeon, prove to be simple and reliable in testing infant cognition before they have gone through certain developmental stages.
Some of the first looking-time experiments Luo conducted while she was in graduate school tested very young infants’ understanding of object permanence. In these studies, she showed the babies events during which an object moved behind two screens. In one setup, the infant would see the object appear in between the gap in the two screens. In another setup, the object would not appear in the gap. Comparisons between these two situations showed that young infants can grasp the reality that an object should be permanent and therefore should not disappear behind the screens. Such results allowed Luo to start thinking more deeply about what other physical concepts infants could manage, such as liquid permanence or transparency.
Since infants are frequently given baths, they are of course exposed to water very early in life. Luo wondered if “maybe they don’t pay much attention to water since it’s colorless and it’s just something weird.” However, she reasoned, “the notion of object permanence should apply to all kinds of objects and substances.” To pursue this question, she began a study with twelve-month-old babies to test whether they recognize that liquid cannot inexplicably disappear or appear. In this experiment, which is presently underway, a screen hides a glass filled with colored liquid. When the screen is raised, the glass is empty. Luo finds that babies are very surprised when the liquid vanishes into thin air. They are also very surprised by the opposite development—when an empty glass becomes full of liquid after being hidden. Another physical understanding experiment involves the perception of transparency. In her initial object permanence study, an object moved behind an opaque screen that infants could not see through. Luo found that infants understood that the object should continue to exist even though they could not see it. But what if they couldn’t see an object that was lowered behind a transparent screen? In this case, Luo has found that babies do not seem surprised until they are about seven and one-half months old, perhaps because their vision may not be developed enough to perceive transparency until about seven months of age.
Another type of experiment Luo conducts revolves around determining the level of infants’ psychological reasoning. About ten years ago, researchers discovered that babies as young as five months old have the ability to understand personal preference given the proper task. Using the looking-time method, babies were shown two different toys, “Toy A” and “Toy B.” They would then watch a person repeatedly choose Toy A to play with, never touching Toy B. Eventually, the person would “change their mind” and choose Toy B. Researchers found that babies were surprised when the person stopped choosing Toy A and switched to Toy B.
Luo decided to take this research one step farther, conducting several variations on the basic experiment: “I wanted to find out if this kind of psychological reasoning in infancy also includes nonhuman objects,” as she puts it. “If we see something moving on its own and we don’t know what it’s made of, we’re probably willing to attribute it to object preferences or goals. We think, ‘Ok, it’s probably moving for a reason.’” To test this hypothesis, she worked with five-month old babies and a “self-moving box.” She presented the same scenario involving Toy A and Toy B, but instead of a human it was a Kleenex-sized box that moved towards the toy for a period of time before changing its preference to choose the other toy. Again, the babies were surprised that the non-human object moved to Toy B. Luo is investigating whether even younger infants are able to recognize this psychological process.
Luo now wonders if her experiments could be applied to younger children, the idea being that “if even two and one-half-month-old babies have the notion of object permanence or some understanding of others’ goals and preferences […] then we could push the age even further back and say, ‘Well, maybe babies are born with some basic physical and psychological knowledge.’”
Watch for Luo’s future research with infants and toddlers on their psychological and physical understanding of the world, as she is sure to challenge longstanding assumptions about these fascinating stages of early childhood.