I want to understand
Jamey Ekins

At every stage of early development, human babies lag behind infants from other species.  A kitten can amble across a room within moments of birth and catch its first mouse within weeks, while its wide-eyed human counterpart takes months to make her first step, and years to learn even simple tasks, such as how to tie a shoelace or skip a rope, let alone prepare a three-course meal. Yet, in the cognitive race, human babies turn out to be much like the tortoise in Aesop’s fable: emerging triumphant after a slow and steady climb to the finish. As adults, we drive fancy sports cars, leap nimbly across football fields and ballet stages, write lengthy dissertations on every conceivable subject, and launch rockets into space.  We have a mastery over our selves and our environments that is peculiar to our species.

Yet, this victory seems puzzling. In the fable, the tortoise wins the race because the hare takes a nap. But, if anything, human infants nap even more than kittens! And unlike the noble tortoise, babies are helpless, and more to the point, hopeless. They could not learn the basic skills necessary to their independent survival even if they tried. How do human babies manage to turn things around in the end?

In a recent article in Current Directions in Psychological Science, Sharon Thompson-Schill, Michael Ramscar and Evangelia Chrysikou make the case that this very helplessness is what allows human babies to advance far beyond other animals. They propose that our delayed cortical development is precisely what enables us to acquire the cultural building blocks, such as language, that make up the foundations of human achievement. Indeed, the trio makes clear that our early vulnerability is an evolutionary “engineering trade-off,” much like the human larynx—which, while it facilitates the intricate productions of human speech, is actually quite a precarious adaptation for anyone trying to swallow safely. In the same way, they suggest, our ability to learn language comes at the price of an extended period of cognitive immaturity. 

This claim hinges on a peculiar and unique feature of our cognitive architecture: the stunningly slow development of the prefrontal cortex (PFC). While other animals’ brain regions development in synchrony, in humans, the development of the PFC lags far behind that of other areas. The PFC is the swath of gray matter that makes up the anterior frontal lobes, and functionally, it appears to be heavily implicated in a wide-range of sophisticated planning and attention driven behaviors. Indeed, it is often referred to as the “control” center of the brain. One of its main functions appears to be that of selectively filtering information from the senses, allowing us to attend to specific actions, goals, or tasks. For this reason, “cognitive control” tasks are thought to be one of the best assessors of PFC function and maturity, and they are tests that young children reliably, and ignominiously, fail.

The Stroop task serves as a simple assessor of PFC function in adults. The task involves naming the ink color of a contrasting color word: for example, you might see the word “red” written in green ink, in which case you have to say “green.” The task is tricky since it demands that we override a well learned response (saying “red” in response to seeing the word red) with a new response specific to the task (naming the conflicting ink color). Tricky or not, healthy adults can successfully complete the task with only minor hesitation.

Children, with their immature PFC’s, are a different story. Typically, the younger children are, the worse they are at solving Stroop-like tasks, and under the age of four, they outright fail them. While young children are sensitive, apt learners, and often appear to fully understand what is being asked of them, they are unable to mediate the conflicting demands present in these sorts of tasks, and thus fail them, time and time again. Three-year olds simply cannot direct how they attend to or respond to the world.