Big Answers From Little People

Psychologist Liz Spelke plumbs the depths of infant cognition

by David Dobbs

from Scientific American Mind, October 2006 
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If you’d been blind all your life and could suddenly see, could you distinguish by sight what you already knew by touch — say, a cube from a sphere? Would objects be objects and faces faces, or would they all be confusing patterns? How would you start to make sense of them? If we’re born knowing nothing, how do we come to know anything – for doesn’t every bit of knowledge follow from another?

Harvard psychologist Elizabeth Spelke takes these questions to the people who just may be best able to answer them: babies. Spelke, whose sprawling lab in Harvard’s William James Hall teems with babies and those interested in them, has addressed some of the most fundamental and intractable questions of human knowledge not by ponderous logic or high-tech exploration but by asking infants who can't yet talk, walk, or even crawl. Her lab has what she calls “an insatiable appetite” for infants and toddlers. Through web pages and flyers, letters to daycare centers and pediatricians’ offices, she asks anyone and everyone for diminutive volunteers to watch, usually as they sit in their mothers’ laps, the stagecraft that Spelke and her students use to gauge early understanding of numbers, language, objects, space, and movement.

Spelke’s findings have helped sharply revise our notion of what humans can make sense of in their first days, weeks, and months. In doing so, they offer some of the most substantial evidence to date regarding ancient questions about nature and nurture and innate versus acquired traits. Spelke’s discoveries about early infant capabilities stand as seminal and central findings in our understanding of early human cognition. And from them she has forged a bold, if still controversial, theory of “core knowledge” that asserts that all humans are born with basic cognitive skills that let them make sense of objects, space, people, movement, and even number. This core knowledge, she says, underlies everything we learn and both distinguishes and unifies us as a species. Her theory touches on ancient questions that remain hot buttons today. As the American Psychological Association put it in 2000 when  it honored her with its William James Fellow Award, “Spelke's research shows that psychological research in cognitive psychology can address some of the most fundamental questions about human nature.” And if these questions still embroil us – and Spelke — in warm debates about our differences, they also suggest, she says, that we all have more in common than we recognize.
 
At the heart of Spelke’s method is the observation of “attentional persistence,” the tendency of infants and children to gaze longer at something that is new, surprising, or different. Show a baby a toy bunny over and over again, and the baby will give it a shorter gaze each time. Give the bunny four ears on its tenth appearance, and if the baby looks longer, you know the baby can discern two from four. The method neatly bypasses infants’ deficiencies in speech or directed movement and instead  makes the most of the one thing they control well: how long they look at an object. Elizabeth Spelke did not invent the method of studying attentional persistence; that credit falls to Robert Fantz, a psychologist at Case Western Reserve who in the 1950s and early 1960s discovered that chimps and infants look longer at things they perceive as new, changed, or unexpected. A researcher could thus gauge an infant’s discriminatory and perceptual powers by showing him different, highly controlled scenarios, usually within a stagelike box directly in front of the infant, and observing what changes in the scenarios the infant would perceive as novel.

Using this basic technique, Fantz and others soon found that the infant’s world was not, as philosopher and pioneering psychologist William James had opined in 1911, a “blooming, buzzing confusion,” and that infants made sense of the world more quickly than even psychologist/philosopher Jean Piaget had established in the 1940 and 1950s. Fantz and other psychologists of the 1960s and 1970s found, for instance, that newborns could differentiate red from green, two-month-olds could discriminate all basic colors, and by three months most babies preferred yellow and red to blue and green. They found that a newborn could distinguish between her mother’s face and a stranger’s (unless both adults wore scarves over their hair), a 4-month-old could recognize acquaintances, and a 6-month-old could interpret facial expressions. By the 1970s, psychologists recognized the first year of life as a far more explosive and significant developmental period than ever before.

This work attracted Spelke while she was still an undergraduate. At Radcliffe from 1967 to 1971, she studied with Harvard’s child developmental psychologist Jerome Kagan and quickly found herself hooked on the excitement of studying children to find out essential workings of human cognition. She continued those studies while pursuing her Ph.D. in psychology at Cornell, where the famed development psychologist Eleanor Gibson served as her graduate advisor and a key mentor. Gibson, one of only ten psychologists ever to win the Congressional Medal of Science, had helped drive the revision of infant cognitive abilities with some elegant experiments of her own. Her best known was the “visual cliff,” a piece of heavy glass extending from a tabletop. Would early crawlers avoid the apparent drop-off?  Most wouldn’t, a discovery that helped greatly revise theories of infants’ spatial understanding.

Under such tutelage, Spelke, pondering possible Ph.D. subjects, soon hit upon her own experiment.” At dinner one night,” she recalled as we talked in her office at Harvard, “I was musing with a fellow student over whether, when a baby looks at and listens to something, does the baby perceive these as two separate, unrelated things, or do they recognize a link between the two? How would you find that out? And suddenly I had this image of two visual events going on side by side, like movies, and between them, a loudspeaker that you could switch from the sound of one event to the sound of the other event. Would the baby turn to look at the event matching the soundtrack the speaker was playing? That experiment became my thesis, and that was the first time I was able to start with a general question about how we organize a unitary world from multiple modalities, of binding these impressions into one, and turn it into a ridiculously simple preferential-looking experiment – which actually ended up working!” For indeed, she found babies did recognize the link between sound and sight, switching their gaze back and forth as the soundtrack changed.

So began Spelke’s career of pondering big questions with little experiments on tiny people. This mixed-modality binding experiment addressed the same question that Locke’s blind-man problem did, which is also essentially the “binding problem” that remains a puzzle at the neurological level: that is, how does the brain mesh the signals from different senses into a single impression? Spelke didn’t answer the question about how. But she showed decisively that this ability lies in capacities seemingly innate.

Over the years Spelke has conjured many other similarly elegant and productive experiments on object and facial recognition, motion, spatial navigation, and numerosity (a rough grasp of numerical relationships) . She's able to do so, she says, “because I think like a three-year-old.” By showing babies moving objects and then interrupting their logical speed or course, she has found that even a 4-month-old infers that a moving object will keep moving, but it takes an 8-month-old to grasp the principle of inertia and expect the object’s path will be consistent and smooth. By showing babies different arrays of discs, she has found that 6-month-olds can distinguish 8 from 16 and 16 from 32  but not 8 from 12 and 16 from 24. She has shown babies an actor reaching for one of two objects and found that while 12-month-olds knew which object the actor would grab from his gaze, 8-month-olds did not.

As the data from such clever designs began to mount, Spelke, often either inspired by or collaborating with colleagues such as linguist Noam Chomsky, French research psychologist/neuroscientist Stanislaus Dehaene, and Susan Carey, a colleague at MIT who is now at Harvard, began to develop her theory of core knowledge. Core knowledge systems, says Spelke, are mental “modules” in place at birth for building mental representations of objects, persons, spatial relationships, and numerosity. Somewhat like the “deep grammar” that Chomsky believes underlies all human language, these core knowledge modules, which Spelke says are domain-specific and exist before language, enable infants to organize their perceptions. In infants these systems resemble those in nonhuman primates, suggesting a long nonhuman evolutionary development; a 6-month-old human understands numbers, space, objects, and faces much as does a Rhesus monkey. As Spelke sees it, these cognitive tools underlie all the more complex skills and knowledge we obtain and master as we grow up – complex languages, number manipulation, and other abstract mental operations. They form the basis for the rich cognitive machinery that gets us through life. And we almost completely ignore them.

“Even for adults,” says Spelke, “most of what we know that lets us negotiate the world, to guide our choice of paths through the environment, to understand whether a car down the street might hit us or whether a falling object will hit us or miss us, even what we say as we’re conversing – most of that is complete unconscious. How many things do we do that, as the saying goes, we hardly think about? Most of what we do is like that. We operate on richly structured cognitive systems and processes that aren’t usually accessible to introspection. To me this is one more sign that most of our cognitive workings are much like those of babies and are built on the core knowledge that we had as babies.”

This is what philosophers call a “nativist” theory, opining that certain of our traits are inborn, natural rather than nurtured, and Spelke knows well what a slippery slope this puts her on. For to speak of native abilities is to court speculation about native differences in those abilities. This spring, Spelke found herself involved in the hottest controversy in some time about such possible differences, when she was repeatedly asked for her opinion of Harvard president Lawrence Summers’s remarks that biological disparities might help explain why women occupy so few places in university math and science departments. Spelke, of course, was a natural to turn to regarding this issue, as not only was she a prominent, highly accomplished scientist at Summers's university, but she got there by studying precisely the innate abilities Summers wondered about. Though Spelke hardly seems a scrapper by inclination, she is quick-minded, funny, imposingly well informed, and eminently agile in conversation; she rises quite gracefully to the task of popping Summers’s thought balloon.

“If you look at things Summers’s way,” she told me in her office, leaning forward in her chair with a sly grin, “then to study innate cognitive abilities, like I do, is supposedly to study gender differences. In fact I didn’t know we were studying gender differences at all, because we don’t find any. But since the subject came up” — she spread her hands, clasped them, and sat back in her chair smiling — ”I was happy to tell him about our work.”

And indeed Summers got an earful, if not directly, as Spelke described in several interviews and in a high-profile public debate with her colleague and friend, psychologist Steven Pinker, how voluminous evidence from decades of research shows little if any inherently sex-based differences in infants, in whom ability rather than culture drives response. At those early ages, when culture has its least effect but sex hormone levels are extremely high (as they are during gestation), no sex-based differences have shown themselves in decades of research testing a huge variety of skills and abilities that underlie mathematical thinking. Put a four-year-old in a distinctly shaped room, hide something in a corner, then have the four-year-old close spin around with eyes closed before hunting for it, for instance, and some four-year-olds will quickly reorient themselves in the room and find the object while others will not. Yet the percentage of boys and girls who succeed is identical. So while “indeed there is a biological foundation to mathematical and scientific reasoning” as Spelke put it at her debate with Pinker, “these systems develop equally in males and females.”

Spelke, an unabashed optimistic, believes our growing understanding of cognitive abilities will eventually reduce rather than inspire divisions about our innate qualities.

“This idea that we have native abilities,” she told me, “some find threatening, for it seems to invite the idea that some types of people might be innately better endowed than others. If you’re a nativist about basic core cognitive capacities, as I am, does that also lead you to be a nativist about individual differences, as Steven Pinker is about math and science? These claims of biological bases can proliferate to a point where they end up being evoked to explain everything. But you have to be very careful about what data you use.” The data showing differences, says Spelke, comes from problematic studies whose results are unavoidably colored by culturally driven results, while the data demonstrating sexual discrimination both overt and subtle is overwhelming — everything from parents responding differently to girls than to boys cries to university faculties viewing identical job applications more skeptically when the applicant’s name is a females. Meanwhile, the expanding piles of data on those least tainted by culture — our infants — shows remarkable parity among sexes and races.

“We’re getting evidence for an intricate and rich system of core knowledge that everyone shares and that gives us common ground,” says Spelke. “In a world of so much conflict, I think that’s something we badly need.”