“We do magic tricks.”
That’s how experimental psychologist Susan Carey describes her work with babies and small children to figure out how they figure things out.
Since kids who can’t talk can’t tell what they’re thinking, Carey has been forced to find other ways of discovering what’s going on inside the child’s head.
Carey and her colleagues have created “look” experiments, where they measure how long a child stares at something as a way to measure whether the child is surprised at what it sees. That surprise is an indicator of whether the child is finding what it expects to find in experiments. Through repeated trials of similar experiments, researchers can see if the child is learning by observing whether or not it continues to be surprised.
Carey, a newly appointed professor of psychology, is part of a three-professor team of cognitive psychologists that gives Harvard one of the nation’s leading programs in this area. Much of the current thinking about the development of thought has come from the group, which includes psychology professors Marc Hauser and Elizabeth Spelke, another recent appointment.
Carey’s current work is two-pronged. She is examining the development of a child’s concept of numbers and looking at a child’s understanding of living things.
The contrast between the two make them good study subjects. Children seem to be born with an innate mathematical understanding, while their understanding of living things seems to be wholly learned.
“I would argue that the human capacity for mathematics is supported by very rich innate knowledge and has a long evolutionary history,” Carey said. “We constantly keep track of quantity. … We’re exquisite correlation detectors. We’re statistical machines.”
While numbers seem to be natural, a sense of biology – or knowing the difference between a rock and a frog – seems to develop around the time a child is age 6 or so.
“Intuitive biology is really interestingly different, because there isn’t any innate system of biology,” Carey said.
Carey, who came to Harvard from New York University, where she was a psychology professor, said her experiments require a large database of babies, assembled from public records and by approaching preschools and day care centers. Graduate students, postdoctoral students, and some undergraduates contact parents and ask them if they’re interested in taking part in the ongoing experiments.
A surprising number say yes, Carey said, and tests are run nearly every day at the still-being-renovated lab space in William James Hall.
“Parents like bringing their babies in,” Carey said. “Their babies are their most interesting thing, and we’re as interested in them as they are.”
The experiments on babies are designed with their short attention span in mind. One experiment, for example, positions the baby before a small stage. A hand puts a Mickey Mouse doll on the stage. Then a screen briefly blocks the baby’s view. While the screen is up, the experimenter can openly add another doll, a “1 + 1 event.” When the screen drops, the baby merely glances if the outcome is the expected two dolls, but stares at the impossible outcomes of one or three dolls, showing he or she has a sense of how many dolls there are supposed to be.
“We do magic tricks. If they have the knowledge that is violated by the magic trick, it’s attention-getting,” Carey said.
While much of Carey’s work is with preverbal children, she also regularly works with older children. Now that she’s back at Harvard, she’s working with some 5- and 6-year-olds who were babies when she worked at the Massachusetts Institute of Technology (M.I.T.), where she was assistant, associate, and full professor between 1972 and 1996, before heading to New York University.
On several experiments, she’s teamed up with Hauser, who is doing similar research from the other side of the evolutionary fence. Hauser uses monkeys to explore the development of thought. Together, they’ve conducted comparative experiments using similar techniques – now adopted by Hauser for his experiments – to produce comparable results.
The results show we humans aren’t quite as superior as we might comfortably believe – at least initially. In mathematical abilities, adult cotton-top tamarinds and rhesus monkeys beat human babies hands down. But as they get older, the babies catch up and pass the monkeys.
Carey said the babies’ acceleration coincides with their ability to talk and she believes language plays a critical role in the development of cognitive abilities.
“We’re interested in the differences between monkeys and children because children are going to turn into adult humans and monkeys aren’t,” Carey said, “and we can’t find any until we get to numbers in language.”
Hauser said he sought out Carey in the mid-1990s because it struck him that the experimental techniques she helped develop would also be useful in his research on monkeys.
Today, Hauser, Carey, and Spelke are collaborating on several levels, Hauser said. They just won a $1.6 million grant to study number representation in nonhuman primates, babies, children, and adults. Their three labs sponsor a weekly seminar and have weekly meetings to discuss developments.
“Basically, what we have now is a team,” Hauser said. “Our plan is [that] for many years to come we’ll have a group in comparative cognition.”
Doing the deeper work
Carey received her Ph.D. from Harvard in 1971 but it was as an undergraduate at Radcliffe College in the early 1960s that she got her start in the field of cognitive development.
Carey, whose father was a research engineer for the National Academy of Sciences, was always interested in math and science, and was initially a biology major. She knew even then that the fit wasn’t quite right, though.
“When I learned math and science I was interested not only in the subject, but in how someone ever even thought of that,” Carey said.
The turning point came in her sophomore year, when she had a tutorial in biology – her major at the time. The postdoctoral student she did the tutorial with was studying biochemical mechanisms that help certain bugs know how it was time to swarm.
Rather than having Carey help him with his experiments, however, he saw that her interests were a bit different and had her look up the literature on animal thought, meeting with her weekly to discuss her readings.
“He was interested in the biochemical mechanisms underlying their representation of time, but I was interested in how researchers knew that these insects could tell time,” Carey said. “At the end of the year, he said, ‘You can do this work in ethology [animal behavior], but … the deeper work on this is happening in experimental psychology.’”
“I don’t remember his name, but I wish I did because I’d like to thank him.”
Carey took his advice and enrolled in Social Sciences 8, taught by two of the leading cognitive scientists of the time, George Miller and Jerome Bruner.
“Primed by him and that course, that was it,” Carey said. “Basically it was a way of finding the discipline that thought about the issues that I had an antecedent interest in. I had thought [all] psychology was clinical psychology.”
In teaching, Carey strives to aid the development pattern she traced at Harvard. With undergraduates, she tries to get them to see the relationships that make up the basics of psychology at the same time as she works to get them to think critically and imaginatively.
She tries to put that imagination and critical thinking to work with her graduate students, guiding them toward projects that they’re interested in.
“What’s really important is that the students leave this place with a research program that is identifiably theirs,” Carey said. “For most students it doesn’t happen until the second or third year when they turn a corner and make it their own. I love to see that moment.”