Welcome to Your Brain (15 page)

instructions.

Linguists have searched through the languages of the world, cataloging differences and

similarities in an attempt to define these parameters. This is slow work, in part because

many languages are related to one another. For example, French, Spanish, and Italian are

Romance languages, which have similar-sounding vocabularies because they are descended

from the same older language. For this reason, the best examples to test the universal

grammar hypothesis are the most unusual languages, which are least related to the world’s

major languages and thus hardest for scientists to identify and analyze.

More reliable support for this idea comes from attempts to teach people artificial

languages that don’t follow the universal grammar rules. For example, various educators of

deaf children have tried to invent new sign languages that are closer to the local spoken

language. Most such languages do not follow the rules of universal grammar, and the

children do not learn them well. What commonly happens is that children learn the language

“incorrectly”—changing it to conform to universal grammar rather than accepting the

artificial language as presented by the teacher.

When does the sensitive period for learning a native language end? This question has been hard to

answer because almost all children are exposed to language early in life; if they aren’t, they’ve

usually been abused in other ways as well. However, one group—deaf children—often learns

language late in the context of a normal life, and so has been much studied.

Deaf children are almost always born to hearing parents, and some of these children don’t start

learning sign language until they go to school. Some deaf children don’t meet anyone who knows sign

language until adolescence or beyond. When they do learn language, they use gestures rather than

sounds. Despite the use of gestures, sign language is very comparable to spoken language. Sign

language has grammar; for instance, American Sign Language has a grammar that is similar not to

spoken English but to Navajo. Just like spoken language, sign language isn’t one language, but a group

of quite different languages. A deaf person from Britain would have no luck communicating with a

deaf person from the U.S. unless one of them had learned the other’s sign language, although the two

countries share a spoken language.

Signed and spoken languages use similar brain mechanisms. They both involve the same language

areas, which are in the left hemisphere in 97 percent of people. Broca’s area in the frontal lobe of the

cortex is responsible for producing language, and Wernicke’s area in the temporal lobe is responsible

for understanding it. Signed languages also have emotional tone, which in speech is called prosody.

Prosody is generated in regions of the right hemisphere that correspond to Broca’s and Wernicke’s

areas. The two types of languages follow similar grammatical rules (see
Did you know? Is language

innate?
), and there’s even a sign language equivalent of an accent in which poor speakers

consistently get their finger and hand shapes a bit wrong. So signed and spoken languages have deep

similarities, suggesting that studies of late learners of sign language can give us valid information on

the limits of spoken-language learning.

As expected, children who learn sign language when they’re younger are more fluent than children

who learn when they’re older. Up to age seven or eight, children are able to learn additional

languages, spoken or signed, without any noticeable problems. Children who learn after the age of

twelve almost never end up using sign language fluently; typically they have poor grammar and an

accent (see above). Between these ages, there’s a lot of individual variation in how well children

learn sign language.

Some of the kids who learn at intermediate ages have accented but grammatically correct sign

language. Similarly, hearing children retain the ability to pronounce sounds like a native speaker until

some time in elementary school. The ability to learn grammatical rules seems to extend even further,

maybe into junior high school. At some point, though, almost everyone reaches an age after which any

new language will be learned as a second language.

Did you know? Is music like a language?

Both music and language involve elements arranged into sequences that are variable but

follow certain rules. This similarity led scientists to consider whether the brain might

process these two types of information in the same way. So far, the verdict is mixed.

Functional imaging shows that tasks involving musical harmony activate Broca’s area,

which is necessary for speech, and a corresponding area in the right hemisphere that is

important for prosody (intonation, which tells a listener when you’re being sarcastic, for

example, or asking a question). Music and language also both activate brain areas involved

in the timing of auditory information. However, people with brain damage can lose their

language abilities without losing their musical abilities, and vice versa, so these two

functions are at least partly separated in the brain. There’s no reason that this question

needs to have a yes or no answer: it’s likely that the brain areas that process language

overlap partially, but not completely, with those that process music.

If this view is correct, it might offer a scientific basis for the widely held belief that

childhood training is necessary for the achievement of high musical skill. Some aspects of

auditory development do benefit from experience. In laboratory animals, the map of sound

frequency in the auditory cortex requires normal experience during a sensitive period. In

people, responses to tones do not become adultlike until the age of twelve or so. In deaf

people, these responses remain abnormal into adulthood. Pitch perception also is more

easily learned in childhood. Absolute pitch (the ability to recognize tones in isolation,

instead of by their relationship to other notes) seems to require both a genetic

predisposition and relevant auditory experience before age six. Absolute pitch is more

common among people who speak tonal languages, such as Chinese, in which pitch is

important for distinguishing words.

Is there a sensitive period for musical training in particular? The brains of adult

professional musicians and nonmusicians differ anatomically, but this could be due to

genetic differences. Musicians’ brains also have different electrical responses, which are

specific to the notes produced by their own instruments, and so probably result from

experience. Some of these effects are more pronounced in musicians whose training began

earlier in childhood, before age ten, and harmonic structure is thought to be easier to learn

before age eight. All in all, we’d bet that musical training in early life does pack some extra

punch, but later training has at least some effect as well. Stravinsky, for example, trained as

a lawyer and didn’t begin composing until he was twenty.

The range of ages at which different language skills become less plastic illustrates another

important point about sensitive periods: their timing is different for different types of learning. The

time window for learning the sounds of a language happens earlier than the window for learning

grammar. Along the same lines, the ability to see motion appears to develop earlier than the ability to

see objects (see
Chapter 6)
. That means there’s no such thing as a single broad sensitive period—

only specific sensitive periods for particular types of learning.

Fortunately, society places limits on the experiments that can be done with babies, so scientists

have turned to other species for insights into the biology of sensitive periods. Songbirds like zebra

finches, for instance, have to learn their individual tunes from other birds, usually their fathers. If a

young male has no one to learn from, he’ll end up with a weird-sounding song that won’t help him

attract a mate as an adult.

Like babies, young songbirds are not infinitely flexible in what they can learn. Zebra finches

raised by a closely related species, the Bengalese finch, do not learn the Bengalese song correctly. In

some cases, a zebra finch will copy a few sounds from his foster father’s song, but he will put these

sounds into a typical zebra finch note sequence, which seems to be innate.

You may think you suffer from information overload in your daily life, but imagine what it’s like

to be a newborn. Without some way to separate the relevant from the irrelevant stimuli, babies might

spend their energy learning to imitate the sounds of birds, or the washer and dryer, which would lead

them to a very strange social life when they grew up. Luckily for all of us, the brain does not come

into the world as a blank slate after all, but has its own firm ideas about what it should be learning.

Chapter 12

Rebels and Their Causes: Childhood and

Adolescence

We like to think of ourselves as sober, responsible adults—gainfully employed, settled down, that

kind of thing. But we were not always such upstanding citizens. Between the ages of thirteen and

twenty-three, we had no fewer than five car accidents and three trips to emergency rooms between us.

All these events were probably at least somewhat preventable, given that our lives have been far less

dramatic since that period. Fortunately, we arrived in adulthood more or less intact—and able to

write about what our brains were up to during that stormy time.

During adolescence, brains and bodies undergo great changes that accompany the transition into

adulthood. This transition can include attaining greater independence from parents, taking on

responsibilities such as a job and a family, and going through periods of emotional turmoil. This last

type of transition is likely to be driven by changes in the brain. Young adults across a variety of

mammalian species, including humans, have poor impulse control and are more likely to take risks,

compared to younger animals or adults. Around puberty, many mammals also become more focused

on social interaction and place a high value on novelty.

These changes may be a consequence of the late formation of some brain systems in youth. Over

the course of adolescence, young adults show improvements in the planning and organization of

behavior, response inhibition, attentional capacity, memory, and emotional self-control, suggesting

that these systems are still developing. Although the brain has reached 90 percent of its adult size by

the age of six, during the last 10 percent of growth, a lot is going on. Connections are being formed

rapidly, but different brain regions develop at different rates. Some of the last connections to be

formed are in the prefrontal cortex, a brain region that is important in moral reasoning and planning

for the future. Adolescents may be only partway down the road toward having a fully functional set of

prefrontal connections.

Practical tip: Improving your brain with video games

Instant messaging, cell phones, e-mail, TV, video games, animated billboards—the

modern world is full of nonstop action, and it all seems to be happening at once. If you’re

over thirty, you’ve probably wondered why younger people aren’t overwhelmed by all this

stimulation.

The reason is that their brains are trained to handle it. Sustained practice at multitasking

increases one’s ability to pay attention to many things at the same time. A major source of

practice is playing action video games—you know, the kind that parents hate, where the