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Learning the language of the brain

Pitt-CMU research center attacks problem of how the adult mind learns and perceives sounds

Monday, November 16, 1998

By Sharon Voas, Post-Gazette Staff Writer

Kae Nakamura of Tokyo braces her hands on her knees like a shy schoolgirl. In her slightly broken English, she says she has learned to say "rock" and "lock." The "R" and "L" roll off her tongue as clearly distinct sounds.

Nakamura, 36, a researcher at the Center for the Neural Basis of Cognition in Oakland, has yearned to be able to tell "R's" from "L's" since she was a schoolgirl studying English in Japan. She struggles to hear the difference between the cradled-tongue sound of an "R" and the tooth-tapping sound of an "L."

Japanese people who come to America as adults usually can't distinguish "R's" from "L's" - no matter how hard they study, no matter how hard they try - because they don't hear the difference. It has become a painful stereotype. But Nakamura learned to say distinct "R's" and "L's" in some words when she participated in an experiment on retraining the brain.

Since she moved to the United States 16 months ago, the tall, thin scientist has been surrounded by conversations that to her are the verbal equivalent of reading a newspaper with all the "R's" and "L's" cut out. She has to guess at the meanings of words rushing past her in these Swiss cheese conversations.

"Most of the time in daily conversation is OK, but writing down is hard," said Nakamura, who studies what happens in the supplementary motor area of the brain during mental processes. "I can't remember whether to use "L" or "R" to write down.

One day she tried to tell her secretary she had bought a Walkman. Her secretary kept asking: A what? A what?

Nakamura heard the difference between an "R" and an "L" for the first time a few months ago when she participated in the study.

She struck keys on a laptop computer to indicate whether she was hearing "R's" or "L's" while the computer voice on her headphones randomly chanted: "road, load, load, road, load" and "rock, lock, rock, lock, lock." The "R" and "L" sounds were computer modified to exaggerate the difference.

She heard it.

Nakamura was in a preliminary study in which Japanese adults were trained to hear the difference in sounds during three, 20-minute sessions. The study is directed by James McClelland, co-director of center, a joint effort of Carnegie Mellon University and the University of Pittsburgh.

"These people have been trying for years, and then they trained for an hour and they've got it," McClelland said with an enthusiastic grin.

The Japanese people in the study learned to distinguish the "R" sound in "rock" from the "L" sound in "lock." But they didn't learn to tell all "R's" from "L's" in general conversation. However, the study indicates Japanese adults can learn to tell the difference and is a first step in learning how to train them to break through their years of hopeless frustration.

McClelland, who teaches psychology and computer science at Carnegie Mellon and neuroscience at Pitt, says the study disproves the long-held belief that people lose their capacity to learn the new sounds of a foreign language when they become adults. That is highly controversial.

He reported his results last week at the Society for Neuroscience annual meeting in Los Angeles.

What McClelland and his colleagues, Bruce McCandliss and Julie Fiez , learn in their ongoing "R" and "L" studies will provide insight into how to help people learn in situations where the brain's ability to learn has seemed frozen. Ultimately, it may help people learn new sounds in other second languages and stimulate learning in children with learning disabilities, amnesiacs and people with brain damage from strokes and other causes.

"We're figuring out how we can reprogram the brain, how we can change these things people thought were hard-wired in the first few years of life," McClelland said. "We're studying the 'R' and 'L' thing because it seems to be a useful place to go after these problems."

"His work is very much in line with the whole new approach to this, which focuses on the brain's capacity to adapt," said Dr. Edward Jones, president of the Society for Neuroscience and director of the Center for Neuroscience at the University of California at Davis.

"It's very promising," he said. "There are already a number of studies underway to attempt to use methodologies in stroke patients that are very similar to what he's using. It's a field we in society should be keeping a close eye on because it offers the promise of enormous improvements in these cases."

McClelland began pondering the puzzle a couple of years ago. Why is it, he wondered, that people can learn new things as adults - how to roller-blade, coordinate their flailing arms and legs to use a Nordic Track, even how to speak a new language - but can't learn certain new sounds in a second language?

Our minds organize many things, such as perception of the pitch of different sounds, by mapping them out across a space in our brains - as if we were taking a blank outline of the United States and sketching the states across it. The brain has only so much space and many things competing for that space. To organize space efficiently, the mind has to decide which things to treat as different - giving them separate representations on the brain map - and which things to treat as the same and clump together, McClelland believes.

Nakamura, like all of us, was born with a fairly blank map where her mind could have sketched in any of the natural sounds made in any language. But, as she heard conversation around her in Japan, McClelland believes, she heard one sound, like that in samurai and Nakamura, that is somewhat similar to the two English sounds "R" and "L." Although our brain imaging technology is not precise enough to measure such things, McClelland thinks it is as if, in native English speakers, the areas of the brain where "R" and "L" register are separate, but slightly overlapped. In Japanese people, they completely overlap.

McClelland set up the experiment to focus people's minds on the difference in making a distinction in just one pair of words - either "road" and "load" or "rock" and "lock" - so those sounds wouldn't be competing with other sounds for space on the brain map.

He gave 16 Japanese adults laptop computers with plug-in headphones to take home to a quiet room. Half of them heard the words pronounced in such a way that a native English speaker could tell the difference between the "L" word and the "R" word.

The other eight started out with pronunciations that were exaggerated by a computer. Once they could hear the difference between "rock" and "lock" in the exaggerated computer speech, they heard progressively less exaggerated pronunciations until they were at the least distinct level that native English speakers could discern.

"All of the subjects who got the exaggerated stimuli learned over the course of three 20-minute sessions," McClelland said. That is "quite rapid - especially in view of the fact that many of them have been in the United States quite a while and never learned these distinctions."

But those who didn't hear exaggerated pronunciations also learned well - with the exception of the two who were the worst at hearing any distinction between the two letters at the start of the trial.

So the critical factor in training, McClelland concluded, is preventing competition from other sounds by giving just one pair of words. Exaggerated differences were needed only to train the people who had the very hardest time hearing the distinction.

Now McClelland is trying to figure out what parts of the training are critical to reprogramming the brain, and how to teach Japanese people to distinguish "R's" from "L's" in everyday conversation.

He will take a cue from another researcher, David Pisoni a psychologist at Indiana University, who has also taught Japanese adults to learn to distinguish "R's" from "L's." Pisoni's method was slower - getting only 6 percent improvement over three weeks of training in one study. But he trained people to distinguish the two letters in a situation more like natural conversation by using a variety of speakers and a variety of words, because the sound of the letter changes with its context in a word.

McClelland wants to combine his focused training on pairs of words with Pisoni's methods in the hope that people will learn faster and learn how to hear the difference between the two letters in everyday conversation.

He will also use brain imaging methods to study the areas of the brain that change their activity as Japanese adults learn "R" and "L." He will look at whether the same areas of the brain are used when listening to sounds learned in childhood as those used in learning new sounds in adulthood.

"There's just so much we can learn to help people," McClelland said.

Nakamura is waiting, eager to learn to hear two letters that are woven throughout the conversation around her.



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