How do infants first acquire concepts—through inborn mental machinery or through a systematic learning process? These two positions, known as nativism and empiricism, respectively, are the leading theoretical approaches to answering this controversial question about cognitive development.

At APA's 2009 Annual Convention, APA honored Harvard University psychologist Susan E. Carey, PhD, a leading proponent of the nativist side, with its Distinguished Scientific Contribution Award. Carey shared her thoughts on the debate and outlined her support for nativism.

"The problem I've been interested in my whole career is what makes it possible for humans beings to think the kinds of thoughts we can think?'" Carey said. "We're the only animals who can ponder global warming and pancreatic cancer."

For conceptual learning to occur, she said, the mind must first recognize and order information through primitive mechanisms. Somehow, adult humans take this initial organization and emerge with full-fledged concepts. The question is how the mind gets from the former to the latter.

The empiricists maintain that the brain's initial setup is lean, composed mostly of sensory-motor functions. Through trial and error, classical conditioning and other types of learning, the brain gradually builds its stock of concepts. Nativists believe that in addition to such innate sensory-motor primitives, there are also perception representations, such as representations of depth, that are innate, and even conceptual representations, such as representations of cause or time, Carey explained.

Carey and other nativists believe that people are born with core cognitive modules that apply to a narrow range of interactions with the world, such as understanding object permanence or the fact that some things act intentionally, she said. These modules have a long evolutionary history that is shared by other primates and, in some cases, even with all vertebrates.

"These are very ancient systems of representation," Carey said.

In support of her theory, Carey pointed to evidence that infants can tell the difference between a small amount of crackers and a larger number, when both are fewer than three. According to her research, infants prefer and crawl toward three crackers they've seen placed into a bucket rather than either one or two crackers placed into a bucket.

But when the number of crackers in any bucket exceeds three, the babies choose randomly. That's because any number larger than three overloads their primitive mental representation system, Carey said.

Because adults routinely keep track of sums much vaster than three, there must be some expansion of these innate concepts. "The adult conceptual system is totally different from the innate starting point," Carey said.

It's more robust and in many ways is defined as the opposite of innate concepts: They're not necessarily domain-specific—they account for many aspects of the world—and they're not shared with other animals.

Carey thinks that humans use a technique she calls "Quinian bootstrapping" (after the philosopher W.V.O. Quine) to build complex concepts out of primitive ones. According to this theory, infants learn conceptual symbols, such as numbers or cardinal values, separately, and later relate these symbols to one another, which leads them to infer larger concepts. For instance, babies eventually put together the fact that numbers match up to the sequentially occurring words "one," "two," "three" and so on, and that allows them to make the conceptual leap to understanding that numbers have a sequential order that constitutes counting.

Eventually these concepts become robust enough to imagine and comprehend such complex phenomena as cancer and climate change.