Thursday, April 11, 2013

Study Shows Children Grasp Grammar While Chimps Only Imitate

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Study Shows Children Grasp Grammar While Chimps Only Imitate
Apr 11, 2013 | Red Orbit | April Flowers

Children as young as two years old understand basic grammar rules and are not simply imitating adults as they first learn to speak, according to a new study from the University of Pennsylvania.

The study was led by Charles Yang, professor of linguistics in the School of Arts and Sciences and of computer science in the School of Engineering and Applied Science. Yang applied the same statistical analysis to data as that used in one of the most famous animal language-acquisition experiments – Project Nim. His finding show that Nim Chimpsky, the famous chimpanzee who was taught sign language over many years, was never able to grasp the rules of language in the same way that a human 2 year old does.

There has been a long-standing debate amongst linguists over whether children actually understand the grammar they use or are simply memorizing and imitating the adults around them. One challenge inherent in resolving this debate relates to the limitations of the data. Since children at that age usually have very small vocabularies, the number of grammatical experiments that they can make is limited compared to that of an adult.

“While a child may not say very much, that doesn’t mean that they don’t know anything about language,” Yang said, “Despite the superficial lack of diversity of speech patterns, if you study it carefully and formulate what having a grammar would entail within those limitations, even young children seem very much on target.”

Yang’s study, published in a recent issue of Proceedings of the National Academy of Sciences, looked at one area of grammar that is regularly displayed by young children known as article usage. This involves their ability to correctly put “a” or “the” before a noun. Yang analyzed nine data sets of children’s speech and found a sufficient number of examples of article usage to conduct the study. The challenge, however, was determining whether the children understood the grammar rules they were using.

“When children use articles, they’re pretty much error free from day one,” Yang said. “But being error free could mean that they’ve learned the grammar of article usage in English, or they have memorized and are imitating adults who wouldn’t make mistakes either.”

To overcome this challenge, Yang exploited the fact that although most nouns can be paired with either the definite article (“the”) or the indefinite article (“a”) to produce grammatically correct phrases, they have different meanings and usages. The combinations vary in frequency because of these differences.

To understand the difference between the definite article and the indefinite article, picture a plate of cookies. There are peanut butter cookies, snicker doodles, ginger snaps and one chocolate chip cookie. If someone asked for “a cookie” it could mean any of the selection on the plate, making it ‘indefinite.’ However, if someone asked for “the chocolate chip cookie,” they are being very ‘definite’ about which cookie they want.

The difference between the two types of grammatical articles leads to a difference in their respective frequency of usage. As an example, “the bathroom” is more commonly used than “a bathroom,” and “a bath” is more common than “the bath.”  It is not a difference in grammar, but opportunity. There are simply more opportunities in day-to-day speech for a phrase like “I need to use the bathroom” or “the dog needs a bath” to be used than phrases such as “there’s a bathroom on every floor” or “the bath was empty.”

Thus the likelihood of using a particular article with a given noun is not 50/50. Usage is weighted towards either “the” or “a” depending on the noun in question. Yang used general statistical laws of language to characterize the lopsided combination tendencies and to develop a mathematical model for predicting the expected diversity of noun phrases.

Yang’s model was able to differentiate between the diversity of usage that would be expected if a child understood the grammar rules compared to if they were only imitating adults. Because of the differences of usage frequency, an adult might only say “the bathroom” to a child, never using “a bathroom.” If the child understood the underlying grammar, however, he or she would still be able to use “a bathroom” correctly.

“When you compare what children should say if they follow grammar against what children do say, you find it to almost indistinguishable,” Yang said. “If you simulate the expected diversity when a child is only repeating what adults say, it produces a diversity much lower than what children actually say.”

Nim Chimpsky – named for world-famous MIT linguist and philosopher Noam Chomsky – was born in 1973 at the University of Oklahoma’s now defunct Institute for Primate Studies (IPS). He was first taught sign language in New York City by Columbia University psychology professor, Dr. Herb Terrace. Terrace raised Nim as though he were a human child in an effort to prove that Nim could learn to communicate through sign language.

Nim continued his education in American Sign Language in several settings, including returning to Oklahoma for many years to work with other famous signing chimpanzees like Washoe and Lucy, before spending his last years at the Black Beauty Ranch in Texas. Nim passed away in 2000 from a heart attack at the age of 26.

Yang applied the same predictive model to the data set of Nim Chimpsky’s signed phrases as a comparison. This data set is the only spontaneous language usage by an animal that is publically available. His findings support what many scientists – including Nim’s own trainers – long suspected about Nim: the sequences of signs he used did not follow from rules like those in human language.

Instead, Nim’s signs were similar to the expected diversity of memorization and imitation rather than that of a systematic grammar. This suggests that true language learning is a uniquely human trait that is present very early in the development of language acquisition.

“The idea that children are only imitating adults’ language is very intuitive, so it’s seen a revival over the last few years,” Yang said. “But this is strong statistical evidence in favor of the idea that children actually know a lot about abstract grammar from an early age.”

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