© Gary Ramage / Newspix / Rex FeaturesHe may not be conjugating Latin verbs, but this cotton-topped tamarin can remember some simple grammar
Primates can intuitively recognise some rules of grammar, according to a study of cotton-topped tamarin monkeys (
Saguinus oedipus).
The findings do not mean primates can communicate using language, but they do suggest that some of the skills required to use language may be linked to very basic memory functions.
One grammatical structure that is found across many languages is affixation: the addition of syllables, either at the beginning or at the end of a word, to modify its meaning.
For instance, in English, the suffix " - ed" is added to verbs to make the past tense. In German, the same effect is achieved by adding the prefix "ge - " to the front of verb stems.
Ansgar Endress and colleagues at Harvard University thought that, because this structure is found in so many languages, it might be linked to basic memory functions that are independent of language. If they could prove this was true, it would suggest ways that children might be learning grammatical structures.
Nonsense wordsTo test this, Endress and colleagues studied 14 cotton-top tamarins, which, like all other non-human primates, do not use language to communicate.
They first played a sequence of nonsensical "words" to the monkeys that all had the same prefix, like "shoybi", "shoyka", and "shoyna".
The following morning, the animals were played a different set of entirely new words. This second set had completely different stems - brain, brest, and wasp instead of bi, ka, and na - but were preceded by the same prefix. Mixed in to the new batch of words were a few that violated the familiar prefix pattern by having a suffix instead of a prefix ("brainshoy" instead of "shoybrain").
The researchers hypothesised that, if the monkeys were able to recognise the prefix pattern they had heard the day before, they would be more likely to look at the loudspeakers when they heard a word that violated the grammatical pattern.
"This is exactly what they did," says Endress. The team found the same result if they familiarised the monkeys with words that had suffixes, then mixed in a few prefixes.
No foodThe fact that the tamarins appeared to understand the prefix and suffix patterns, without being trained with food rewards, does not prove that they have language and grammar, says Endress. But it does suggest that their memory is able to recognise certain linguistic patterns.
Memory organisation in humans means we find it easiest to track what occurs in the first and the last position of sequences. "This is a basic and well-known fact about the organisation of memory for sequences," says Endress.
"If you try to remember the sequence NBGHQPZRXV, it is easier to remember that N was in the first position, and V in the last position," than it is to remember that the H was in the fourth position.
The results suggest that grammar may have evolved from this basic memory structure. It could also explain how rules like the English past-tense are learned.
Endress explains: "Our results suggest a fairly pedestrian mechanism: human infants, like monkeys, might be particularly prone to track what occurs in the first and the last position of words and other linguistic units. They might use these mechanisms of memory organization for learning affixation rules."
Kate Arnold of the University of St. Andrews, UK, says the finding that some primates are able to differentiate a valid sequence from an invalid one may relate to some very unusual behaviour she has seen in wild monkeys. Last year, Arnold showed that putty-nosed monkeys in Nigeria are able to combine two different calls into a sequence that causes other monkeys in the area to move to a different area. This is the closest anyone has ever come to observing animals using syntax.
Journal reference:
Biology Letters, DOI:
link (in press)
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