July 7, 2009 -- Cotton-top tamarin monkeys may look like little fluff balls, but these primates are not lightweights when it comes to learning at least one basic component of language. A new study found that these monkeys can tell the difference between prefixes and suffixes.
The discovery, reported in the latest Royal Society Biology Letters, suggests non-human primates, and possibly many other animals, share some skills associated with human language.
In this case, distinguishing prefixes from suffixes requires a good memory and an understanding of sequence.
"For example, if you try to remember a letter sequence such as NBGHQPZRXV, it is easy to remember that 'N' was in the first position and 'V' in the last position," lead author Ansgar Endress told Discovery News.
Use of prefixes and suffixes relies upon this pattern, which requires learning "a regularity where only specific items can occur in the first or last position," he added. "Our results suggest that cotton-top tamarins -- but presumably also many other animals -- can do so."
For the study, Endress, a researcher at Harvard University's Department of Linguistics, and his colleagues played recordings of human speakers to 14 adult tamarin monkeys. Their spoken affix syllable was always "shoy," while the stems were "bi, ka, na, to, go, lo, ri and nu." Both female and male speakers spoke the sounds, with the voices frequently mixed to prevent the monkeys from simply responding to different pitches and voice levels.
Monkeys first became familiar with a certain pattern, such as "shoy-bi." During the test, the researchers would then suddenly vary that to "bi-shoy," turning what was once a suffix into a prefix. When this happened, the monkeys would turn their heads toward the individual playing back the recordings, a response previously determined to indicate their acknowledgement that the familiar sound ordering pattern had been violated.
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Although monkeys don't understand human words, and "shoy" is just a meaningless syllable, their reaction could be comparable to a person saying he or she "walked to the store," and then using the word "edwalk" instead of "walked." The listener, used to hearing "walked" might stare at the speaker as if to say, "Huh?"
Endress thinks human babies understand such simple affix patterns, just as monkeys do.
"Our results suggest a fairly pedestrian mechanism: human infants, like monkeys, might be particularly prone to track what occurs in the first and last position of words and other linguistic units," he explained. "Hence, they might use these mechanisms of memory organization for learning affixation rules."
Thomas Bever, a professor of linguistics, psychology, cognitive science and neuroscience at the University of Arizona, told Discovery News that Endress and his team "have now shown that tamarins form the concept that a particular speech sound occurs in a particular position in relation to other speech sounds. It is striking that tamarins do this spontaneously without explicit training and with an astoundingly small number of exposures."
Bever added, "The authors' claim that this is evolutionary background for how human children learn suffixes in inflected languages is ambitious, but intriguing."
Endress hopes future studies can confirm the ability in other species, as well as finding evidence for other language-like computations that are based on perceptual or memory mechanisms.
"This would allow us to understand some of the building blocks of language and their evolutionary origins," he concluded.
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