Karela Fry

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The fastest way of learning a language

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If you do not understand the arcane language of a physicist, you may have trouble understanding the method which Reisenauer, Smith and Blythe claim to be the fastest way of learning a language in a recent issue of Physical Review Letters:

We study the time taken by a language learner to correctly identify the meaning of all words in a lexicon under conditions where many plausible meanings can be inferred whenever a word is uttered. We show that the most basic form of cross-situational learning—whereby information from multiple episodes is combined to eliminate incorrect meanings—can perform badly when words are learned independently and meanings are drawn from a nonuniform distribution. If learners further assume that no two words share a common meaning, we find a phase transition between a maximally efficient learning regime, where the learning time is reduced to the shortest it can possibly be, and a partially efficient regime where incorrect candidate meanings for words persist at late times. We obtain exact results for the word-learning process through an equivalence to a statistical mechanical problem of enumerating loops in the space of word-meaning mappings.

So it is good to have the Focus article which explains:

A typical child learns approximately 60,000 words by the time she is 18. Children use many strategies to identify word meanings, including techniques to deal with ambiguous situations. For example, a child hears the word “cup” and at the same time sees a cup, a ball, and a book. She might remember this experience the next time she hears “cup” in conjunction with a cup and a different set of objects (the “confounders”). If the cup was the only object present in both situations, the child learns that “cup” means cup.

If the child further assumes that there is only one name for each object (meanings are mutually exclusive), then she can learn words faster. For example, if she hears “cup” and already knows the meanings of “ball” and “book,” the two other objects present, then she learns immediately that “cup” refers to the only non-assigned object. “It’s a boot-strapping technique, where you use information from previous learning [of words] to eliminate certain meanings,” explains Richard Blythe of the University of Edinburgh in the UK. Small-scale lab tests have shown that children and adults use mutual exclusivity to determine word meaning. But researchers don’t know how effective this strategy is compared with others when dealing with hundreds or thousands of words.

To address this question, Blythe and his colleagues used a physics analogy that others have exploited in the past: word learning resembles some problems in nonequilibrium statistical physics, where a large number of entities (such as molecules) interact, and the probability distributions for certain states evolve over time. In language learning, a word like “cup” will start off with many confounders, and so the probability of “cup” meaning cup will be low. But over time this probability—and that of other word-meaning pairs—will grow to one, analogous to the system approaching equilibrium.

When the team included mutual exclusivity in the model, they found that the learning time dropped dramatically. For a modest number of confounders (around ten), the entire lexicon was learned in the minimum time it takes to hear every word at least once. Words were learned nearly as quickly as they were encountered, suggesting that the mutual exclusivity assumption is extremely effective. The authors speculate that acquiring this word learning strategy may have been an important step for early humans as they developed their language ability.

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Written by Arhopala Bazaloides

June 28, 2013 at 4:55 pm

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