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Thursday, January 14, 2010

CMU researchers find brain has categories for nouns

Wednesday, January 13, 2010
When your brain thinks about words for concrete objects, it asks three basic questions -- can I hold it, can I get inside it, and can I eat it?
That's one way of looking at the bottom line of a new brain imaging study by Carnegie Mellon University researchers that analyzed the "neural signatures" in 11 people's brains for 60 nouns.
Last year, the team led by psychologist Marcel Just and computer scientist Tom Mitchell determined that people's brain patterns for each of the 60 words were very similar, and that a computer program could use the patterns to predict what word a person was thinking of with 80 percent accuracy.
This year, the same team used a technique called factor analysis to determine that people's brain patterns fall into three broad semantic categories.
When they asked the computer to name the top 10 words in each category, Dr. Just said, it seemed clear they fit with the concepts of shelter, manipulation and eating.
The top words in the shelter category, for instance, were apartment, church, train, house and airplane. In the manipulation group, they were pliers, saw, screwdriver, hammer and key. In the eating category, the top words were carrot, lettuce, tomato, celery and cow.
The groupings, Dr. Mitchell said, "were discovered by the [computer] program, and these themes just sort of emerged." When researchers asked people to group the words under those three categories, he said, "they identified the same words."
A key lesson from the results, Dr. Just added, is that people don't primarily evaluate words based on such parameters as size, shape, color or texture, but by what the object means to them personally.
"What the brain cares about primarily is how the person interacts with the object," he said.
David Cox, a vision researcher at Harvard University, said he appreciates studies like this one for "trying to get more of an understanding of the neural basis of language."
Dr. Cox, who studies vision in lab rats, said animal models can't help scientists understand human language, but "functional magnetic resonance imaging can give you a window into that, and carefully designed studies have the potential of opening that up."
Noting he had not read the study thoroughly, he said he was a little skeptical about the labels the Carnegie Mellon team had used for its three categories of brain patterns.
"You always want to worry when you affix a word like eating or shelter or manipulation to a category that there might be something else more parsimonious that explains the categories."
But Dr. Just said the three basic categories make sense to him. "I think this is the way the brain codes objects we encounter. If you pull something out of a closet or drawer, I think the brain evaluates it along those three dimensions."
The team got its results by showing people the 60 words several different times as they lay in a functional magnetic resonance imaging machine, which measures brain activity by monitoring blood flow to different parts of the brain.
The researchers are already working on expanding their brain imaging studies to different kinds of words.
One shortcoming of the noun study, Dr. Just said, is that it doesn't include any words involving social relationships.
But in an unpublished study, the team asked people to think about such verbs as "praise" and "insult," and found that they exhibited distinct neural patterns depending on whether they were thinking, for instance, of insulting someone compared to being insulted.
Another study asked people to think about such abstract concepts as justice and love and found that the participants shared similar brain patterns for those words as well, but the researchers have not yet tried to group those words into categories.
Dr. Mitchell said they are also acutely aware that people don't think in single words, but in sentences and paragraphs.
"We're still at the level of how people understand a word, but now we think it's time to look at word combinations."
Mark Roth can be reached at mroth@post-gazette.com or at 412-263-1130.
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