Anyone who's seen a toddler "at work" can tell that her learning style is a study in chaos. She moves from banging pots to tormenting the cat to demanding food to bursting into tears when she can't open the back door and hurdle off the deck -- all in the span of minutes.
But when it comes to the daunting task of mastering language, that same child is a turbo-charged learning machine.
An intriguing article published Tuesday in the journal Current Directions in Psychological Science suggests credit for that ability should go to what she lacks -- a fully formed prefrontal cortex, the same thing that makes her dad so good at filtering out distractions and getting things done.
Babies are born with the foremost part of the brain -- the prefrontal cortex -- almost completely undeveloped. For children developing normally, it takes about four years for that so-called seat of higher reasoning to catch up with the rest of the brain in size and complexity. (For children with attention-deficit hyperactivity disorder, such maturation takes longer; for those with autism, the prefrontal cortex develops early.)
This would explain why toddlers are inattentive, distractible and live in the moment. When developed, the prefrontal cortex plays a key role in suppressing impulses, focusing on the task at hand and setting priorities among competing demands.
Yet by the time a typical child is 4, she will have learned to speak (in fact, she may never be quiet) and will have learned all kinds of complex cause-and-effect connections -- that climbing up a slide's ladder will yield a fun ride down, that stealing a friend's toy will bring momentary triumph but will also cause her friend to cry and a teacher to intervene.
In those crucial four years, a toddler's accumulation of knowledge about her world may be unhampered by the discipline imposed by the prefrontal cortex, suggests a trio of neuroscientists from the University of Pennsylvania and Stanford University.
Her prefrontal cortex doesn't stand in the way and try to keep her "on task." And her underdeveloped powers of attention will keep her from getting bogged down by pesky exceptions to rules of grammar or syntax. So, she'll always apply the most general rules she knows -- say, that adding an "s" makes things plural.
The authors call this period of disorderly learning "cognition without control."
This is a theory, not a finding, note the authors, led by the University of Pennsylvania's Sharon L. Thompson-Schill: that evolution may have favored a delay in the maturation of the brain's "braking system" as a means of allowing rough-but-rapid learning of complex matters such as language and social conventions. But it's a theory that might help clinicians and educators begin to identify the best windows for teaching very young children and for helping kids with developmental differences to learn as well.