Human brains are slow to develop — a secret, perhaps, of our success.

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.

Thompson-Schill and her colleagues suggest that this inability
to direct attention has important consequences when it comes to
learning about uncertain events. To explain this, it helps to imagine
you are playing a guessing game: You have to choose one of two options,
either A or B, one of which leads to a prize, and one of which does
not. After a few rounds, you notice that about three fourths of the
time the prize is at A, and the rest of the time it is at B, so you
decide to guess “A” 75 percent of the time and “B” 25 percent of the
time. This is called probability matching, and it is the response
pattern most adults tend to adopt in these circumstances. However, if
the goal is to win the most prizes, it is not the best strategy. In
fact, to maximize the number of correct predictions, you should always
pick the more frequent outcome (or, in this case, always pick “A”).

Interestingly, if you were playing this kind of guessing game with a
toddler, you would see that they would employ the maximization strategy
almost immediately.   Thompson-Schill and her colleagues suggest that
this is because toddlers lack the cognitive flexibility that would
allow them to alternate between A and B. Since young children are
unable to selectively switch between responses, they can only choose the most likely option. Fortunately for them, in this guessing game scenario, maximization is the right choice.

While it may not be immediately obvious what this has to do with language learning, it just might have everything to do with it, because language relies on conventions. In order for language
to work, speakers and listeners have to have the same idea about what
things mean, and they have to use words in similar ways. This is where
toddlers come in. Young children, as it turns out, act like finely
tuned antennas, picking up the dominant frequency in their surroundings
and ignoring the static. Because of this – because toddlers tend to
pick up on what is common and consistent, while ignoring what is
variable and unreliable – they end up homing in on and reproducing only
the most frequent patterns in what they hear. In doing so they fail to
learn many of the subtleties and idiosyncrasies present in adult speech
(they will come to learn or invent those later). However, this
one-track learning style means that what they do learn is highly
conventionalized. 

The superiority of children’s convention learning has been revealed in a series of ingenious studies
by psychologists Carla Hudson-Kam and Elissa Newport, who tested how
children and adults react to variable and inconsistent input when
learning an artificial language. Strikingly, Hudson-Kam and Newport
found that while children tended to ignore “noise” in the input,
systematizing any variations they were exposed to, adults did just the
opposite, and reproduced the variability they encountered. 

So, for example, if subjects heard “elle va à la fac” 60%
of the time and “elle va à fac” 40% of the time, adult learners tended
to probability match and include “la” about 60% of the time, whereas
younger learners tended to maximize and include “la” all of the time.
While younger learners found the most consistent patterns in what they
heard, and then conventionalized them, the adults simply reproduced
what they heard. In William James’ terms, the children made sense of
the “blooming, buzzing confusion” they were exposed to in the
experiment, whereas the adults did not.

Children’s inability to filter their learning allows them to impose
order on variable, inconsistent input, and this appears to play a
crucial part in the establishment of stable linguistic norms. Studies
of deaf children have shown that even when parental attempts at sign
are error-prone and inconsistent, children still extract the
conventions of a standard sign language from them. Indeed, the variable
patterns produced by parents who learn sign language offers insight
into what might happen if children did not maximize in learning:
language, as a system, would become less conventional. What words meant and the patterns in which they were used would become more idiosyncratic and unstable, and all languages would begin to resemble pidgins.

While no language is completely stable, there is a balance to be
struck between an individual’s expressivity and the conventions that
underpin it, and children clearly play an important role in maintaining
this balance. Children may learn the established idiosyncrasies of
their community (saying “eggplant” instead of “aubergine” or “parking
lot” for “car park,” for example), but they do so only because these
forms are stable in their input. They are unlikely to adopt highly
unusual or idiosyncratic forms or sequences that they’ve heard only
rarely, and when they themselves make errors, they are similarly
unlikely to incorporate these errors into their language use over the
long run.

Individual societies are built upon these kinds of cultural and linguistic conventions, and a vast array of them. As social animals, human babies must somehow master not just “culture and language,” but the specifics of their culture, and their
language. Explaining how babies manage to learn all of this information
is a formidable task. The research reviewed here reveals one advantage
that nature may have conferred on human infants: when it comes to
convention learning, children’s inability to think unconventionally or
flexibly may be of huge benefit. Indeed, a number of neurological studies
suggest that autistic children, who often exhibit marked language
delays and idiosyncratic language development, experience a massive
overgrowth of the prefrontal cortex over the first two years of life.
It might be that if children were able to think like adults, they
simply could not learn conventions in the same way, if at all. If that
were the case, we might not be winning any races after all.  (…)

 

Source: Scientific American – http://tinyurl.com/ydkowuy