Monkeys have a memory for grammar

Catherine Brahic

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 words

To 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 food

The 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.

Courtesy: New Scientist