From the Warner Brothers movie Fury in the Pacific.
Courtesy National Archives and Records Administration

The unknowable sounds
Ancient enough to remember World War II movies? Then recall that GIs in the Pacific theater chose passwords overrun with R's -- words like "rabble-rouser" or "rubbernecker." The reason was simple: Japanese people have a 'ell of a time with R, which they often pronounce as "ell."

While infants have no trouble distinguishing any sound in any language, by about one year of age, their brains have changed in response to their environment. Like a self-programming computer, it responds to the sounds of the mother tongue by creating neural circuits appropriate to that language.

This slick adaptation has a cost, however, since in the process of learning to speak and understand native languages, children lose the ability to distinguish sounds of languages they don't hear.

Neuroscientists, amazed by the flexibility -- they call it "plasticity" -- of the infant brain, term those early months the "critical period" for language development. After the critical period, they thought, brains could no longer make the new connections needed to completely learn a language.

It's a neural form of the ol' "use it or lose it" proposition, one that would explain the Japanese confusion over R and L.

A similar notion applies to vision, another crowning achievement of the brain. Infants born with two cataracts can only gain perfect vision if the cataracts are removed soon after birth. Otherwise, their developing brains, deprived of visual input, will not wire themselves for perfect vision.

Regularly learning R's and L's
James McClelland, a neuroscientist Carnegie-Mellon University, wanted to explore whether adult brains could learn language sounds decades after the critical period. "It seemed to me that maybe there was more flexibility, more room for learning than people were giving us credit for," he says.

Tule Lake Relocation Center, Newell, California, where Japanese-Americans were incarcerated during World War II. A sixth-grade pupil in the classroom.
Courtesy National Archives and Records Administration

He explains that people who grew up speaking only Japanese cannot hear, much less pronounce, R and L, because Japanese has one category for the two sounds. In fact, he says, the more they hear, but do not distinguish, English R's and L's, the worse the confusion.

McClelland wanted to eliminate the confusion -- to reopen the critical period when the brain can learn sounds.

He wanted to teach old brains new tricks.

He set up a study that played digitally exaggerated the R's and L's to Japanese-speakers. Once subjects pressed a button to indicate that they were hearing two sounds, the exaggeration was reduced, and finally eliminated.

Feeding it back
Most subjects learned to distinguish the elusive sounds in three 20-minute sessions, which, McClelland says, proves that the critical period can be reopened, at least with the right techniques. Equally surprising, learning occurred without feedback about which sound was which.

The omission of feedback tested an old theory of the eminent neuroscientist Donald Hebbs, who maintained that connections between neurons get stronger as signals pass between them. The notion, often reduced to "neurons that wire together fire together," could explain why practice, study and repetition all build stronger memories and better skills.

Student studying in the Multicultural Student Center lounge located in the Armory (Red Gym).
Photo by Jeff Miller ©University Communications

Hebbs's theory could also explain, McClelland says, why his subjects learned to distinguish R and L without feedback. The exaggerated sounds established two separate neural pathways, and thus became separate entities that could be triggered by normal R's and L's.

But the feedback results were mixed, since feedback without exaggeration was almost as effective as exaggeration without feedback. The study is now under review at an academic journal.

Fire & wire
What are the practical implications of knowing that adult brains can learn subtle distinctions in language long after the critical period? Obviously, it should inspire for people trying to learn languages with foreign sounds.

The study, and its emphasis on "fire together, wire together," would also suggest tackling tough sounds early, to prevent early mistakes from getting ingrained. McClelland, for example, speculates that every time a Japanese-speaker hears -- but does not distinguish -- R or L, the confusion intensifies because one neural pathway is being reinforced.

Learning, he stresses, occurs whether we're learning facts or fallacies. If we hear 6 x 7 = 44 and don't recognize the error, that pathway is strengthened just as a different pathway is reinforced when we hear 6 x 7 = 42.

Another lesson is really a chestnut of education. Persistence pays. When learning a new skill, McClelland says, "If we try a little bit and don't seem to have success, we may say 'This is not for me.' If we really focus in and identify where exactly the problem is, we might break out of old habits." After a stroke, you may need to learn to move all over again.