Puzzled monkeys reveal key language step

19:00 15 January 04

The key cognitive step that allowed humans to become the only animals using
language may have been identified, scientists say.

A new study on monkeys found that while they are able to understand basic
rules about word patterns, they are not able to follow more complex rules
that underpin the crucial next stage of language structure.

For example, the monkeys could master simple word structures, analogous to
realising that "the" and "a" are always followed by
another word. But they
were unable to grasp phrase patterns analogous to "if... then..."
constructions.

This grammatical step, upon which all human languages depend, may be "the
critical bottleneck of cognition that we had to go through in order to
develop and use language", says Harvard University's Marc Hauser, who
carried out the study with fellow psychologist Tecumseh Fitch, at the
University of St Andrews, Scotland.

"Perhaps the constraint on the evolution of language was a rule problem,"
Hauser told New Scientist.

Random words

Fitch and Hauser carried out two aural tests on cotton-top tamarin monkeys
in which sequences of one-syllable words were called out by human voices.

In the first test, random words were called out in a strictly alternating
pattern of male followed by female voices. The monkeys responded to breaks
in the male-female rule, by looking at the loudspeaker. This showed that
they were able to recognise the simple rule.

In the next test, the grammatical rule dictated that the male voice could
call out one, two or three words, as long as the female voice did the same.
This type of slightly more complex pattern is called recursive, as it
involves a rule within a rule.

This time, the monkeys were unable to recognise any breaks in the pattern.
But twelve human volunteers given the same test had no such difficulty,
although most were unable to explain what the rule actually was.

"Recursive ability is uniquely human and affects more than just our
language, but most of our behaviour," says renowned primate language expert
David Premack, who wrote an article accompanying the study published in
Science. "For example, in a classroom we often see child A watch child B
watch child C watch the teacher. But in chimps, we see chimp A watch its
mother, chimp B watch its mother, chimp C watch its mother..."

Random words

Fitch and Hauser carried out two aural tests on cotton-top tamarin monkeys
in which sequences of one-syllable words were called out by human voices.

In the first test, random words were called out in a strictly alternating
pattern of male followed by female voices. The monkeys responded to breaks
in the male-female rule, by looking at the loudspeaker. This showed that
they were able to recognise the simple rule.

In the next test, the grammatical rule dictated that the male voice could
call out one, two or three words, as long as the female voice did the same.
This type of slightly more complex pattern is called recursive, as it
involves a rule within a rule.

This time, the monkeys were unable to recognise any breaks in the pattern.
But twelve human volunteers given the same test had no such difficulty,
although most were unable to explain what the rule actually was.

"Recursive ability is uniquely human and affects more than just our
language, but most of our behaviour," says renowned primate language expert
David Premack, who wrote an article accompanying the study published in
Science. "For example, in a classroom we often see child A watch child B
watch child C watch the teacher. But in chimps, we see chimp A watch its
mother, chimp B watch its mother, chimp C watch its mother..."

Human flexibility

Premack argues that although recursive ability is not absolutely necessary
for language - non-recursive sentences are possible - being unable to master
recursion may have been a stumbling block that prevented monkeys from
developing language.

"Monkeys are also not physically capable of speech, they are unable to
properly copy actions and they cannot teach - all of which are skills
required for language," he told New Scientist.

Mastery of the underlying rule of recursion is the key to human flexibility,
Premack believes, allowing humans to think in the abstract, use metaphors
and comprehend concepts such as time. It probably arose as the brain evolved
into a more complex organ, but is not located in a single brain region.

However, it is not known whether modern humans are born with the ability to
recognise recursive language patterns. More research into recursive ability
in humans and their close relatives chimpanzees needs to be carried out,
Hauser says.

Journal reference: Science (vol 303, p 377)

Gaia Vince

>From New Scientist
http://www.newscientist.com/news/news.jsp?id=ns99994572

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