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Monkeys Understand Unspoken Complexities Of Language

July 8, 2009

Human language is a vastly complex system that is nevertheless mastered early in human life. The question is whether the capacity to understand language is unique to humans, or if the ability is shared at least in part by other species.

A growing body of research has revealed clues about the evolution of language.

Researchers said in the journal Biology Letters that the cotton-top tamarin monkeys are able to notice if the order of syllables in a word is incorrect.

They made the monkeys familiar with two-syllable terms, and then recorded their response when they heard words that were not in keeping with the established syllable pattern.

The work illustrates the way many animals use the same patterns that are fundamental to the very nature of human language, according to the team.

This finding provides evidence of the “non-lingual”, unspoken origin of certain aspects of language, the group told BBC News.

In the experiment, the monkeys heard a series of different words that all contained the same first syllable or second syllable in order to observe the origins of the prefixes and affixes commonly found in languages to denote tense.

For example, in English, the past tense of a verb can be made by simply using the suffix “-ed”, making “talk” become “talked”.

They used repetition until the monkeys were familiarized with the pattern of a word by its prefix or suffix rather than the word itself.

Lead author of the study Ansgar Endress explained, “In the prefixation condition, they heard ‘shoy-bi’, ‘shoy-la’, ‘shoy-ro’ and so on.” 

“The idea is that they get used to the pattern if you play it long enough.”

The “suffixation” group heard words with a changing first syllable, this time with the suffix, “shoy”, kept consistent – such as “bi-shoy” and “la-shoy”.

They played the words repeatedly until the monkeys were completely familiar with them, and the monkeys were tested the next day.

The researchers then confronted them with “new” words that were either consistent with the pattern they had heard before, with “shoy” in the right place, or deviating from the familiar pattern.

“We simply measured how often the monkeys looked to the speaker when we played the items,” said Dr Endress.

“If they got used to, or bored by, the pattern, then they might be more interested in items that violate (it) – because they are something new – than in items that are consistent with the pattern.”

Marc Hauser, who was also involved in this study, told BBC News that the results revealed how human language had committed processes to memory that were not “language-specific”.

“Simple temporal ordering is shared with non-human animals,” he said.

“This has an important role. In bird song or whale song, for example, there’s a temporal ordering to the notes and that’s critical for communication.”

The Cotton-top Tamarin vocalizes with birdlike whistles, soft chirping sounds, high-pitched trilling and staccato calls. Researchers say its repertoire of 38 distinct sounds is uncommonly sophisticated, remaining in accordance with grammatical rules and able to express curiosity, fear, dismay, playfulness, warnings, joy and calls to young.

And it goes beyond that. “In primates, this ordering is vital for learning,” explained Professor Hauser. “In tool use, primates learn from each other that you do this first, then you do that, then it’s that.”

Professor Hauser went on to explain how apparent this innate ability is when a child learns language.

“As a child learns to use the past tense,” he said, “they may generalize and use a suffix wrongly, but they will never generalize in the wrong direction.

“You never hear them say ed-walk instead of walked.”

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