MONKEYS are surprisingly numerate, say scientists in New York. They have
found that monkeys trained to rank groups of up to four items in ascending
orders could spontaneously do the same with larger numbers. The finding suggests
that monkeys understand the sequence of numbers, undermining the view that
language skills are required to understand the concept of numbers.
Many scientists believe that numeracy and language ability are linked. Both
require complex mental manipulations and scientists tend to think that animals
that can鈥檛 speak can鈥檛 understand numbers either. Some have even suggested that
numbers are a social construct.
To test the idea, two psychologists at Columbia University, Elizabeth Brannon
and Herbert Terrace, gave a pair of rhesus monkeys called Macduff and Rosencranz
a touch-sensitive video monitor. They then flashed sets of four images on the
screen. Each image contained a different number of elements鈥攖wo circles,
say, or three little flowers鈥攖o represent the numbers one to four. The
researchers varied the elements in terms of brightness, size and arrangement to
be sure the two monkeys were paying attention to the quantity and not something
else, such as area.
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If the monkeys touched the boxes in ascending order from one to four, they
were rewarded with a banana-flavoured treat. If they made a mistake, the screen
went blank and they had to start all over again. After training them for about
six weeks, the researchers put the monkeys through 150 new trials over five
days, with brand new items鈥攋ust to make sure they hadn鈥檛 been using memory
tricks all along. 鈥淣ow we were sure they could differentiate 1, 2, 3 and 4,鈥�
says Brannon.
The big surprise came when the psychologists tested the monkeys with
quantities they鈥檇 never seen before. When they were shown two new images
containing between five and nine items, Rosencranz and Macduff put them in
ascending order. They saw each pair only once and got no reward for getting it
right. Yet they continued to respond with 75 per cent accuracy, Brannon and
Terrace report in Science (vol 282, p 746). 鈥淭hey didn鈥檛 need
training,鈥� says Brannon. 鈥淭hey understood the ordinal relationship.鈥�
Brannon and Terrace think the animals must be somehow predisposed to process
numbers. 鈥淣umbers must be important to them in order for them to show this kind
of spontaneous behaviour,鈥� says Brannon.
Marc Hauser, a psychologist at Harvard University in Boston, says the study
clearly shows that animals can have numeracy skills without language abilities.
He believes the rhesus monkeys are better with numbers than one-year-old babies,
who have begun to develop rudimentary language. He want to find out what happens
in human brains that makes us able to develop the skill to such a complex level.
鈥淎t some point the kids are going to leave the monkeys in the dust,鈥� says
Hauser. 鈥淲hat major cognitive event happens in a child that doesn鈥檛 happen in a
尘辞苍办别测?鈥�
Brannon and Terrace now hope to discover what kind of mechanisms underlie the
monkeys鈥� abilities. 鈥淎re they counting?鈥� Brannon asks. 鈥淗ow are they
representing the numbers?鈥�