It's not only humans who can estimate quantity, reports Dick Ahlstrom
It may sound surprising, but number-crunching isn't only the preserve of humans. Most animals can estimate numbers, allowing them to assess the numbers of friends and enemies and the amount of food they have, delegates to the BA Festival of Science 2003 were told yesterday.
Lions, for example, can "count" their opponents when their prides face off over territory. Monkeys and other mammals, as well as insects such as bees, have the same skills.
Researchers described efforts to discover how we and other animals understand numbers in a session entitled "Where do numbers come from?" The work has also revealed that up to one in 20 children suffers from an inability to do simple arithmetic despite understanding the number theory involved.
Humans use a verbal counting system to do maths, something beyond the capacity of animals. But the use of brain-activity scanning showed that animals and humans have different counting systems, according to Dr Stanislas Dehaene of Inserm, the French Institute of Health and Medical Research. The work was an attempt to understand number sense, our ability to grasp number appreciation. He has identified nerve cells in the parietal lobes of the brain that respond to specific numbers. Each reacts to a different number approximation, one recognising four, five or six, another 12 or 13 and so on. The ability is important for survival, he says. "Numbers are a very basic property of the outside world," whether you are a mouse or a man.
Prof Rochel Gelman of Rutgers University, in New Jersey, described experiments showing how a rat could learn to press a lever up to 50 times to get food, describing it as a "statistical signature of how animals are responding to numbers".
Prof Brian Butterworth of University College London said imaging had shown humans also had this non-verbal ability to approximate numbers. He developed a test in which one side of a computer screen showed a collection of dots while the other showed a number. Subjects looked at it briefly before being asked to say which side signified a larger figure. People were able to respond correctly most of the time. The results also indicated that women came out on top. "Females were very slightly but consistently faster than males," he said.
The test was a good way to help diagnose the up to 5 per cent of children with "discalculia", an inability to do simple verbal maths. "These kids find it difficult to count. They think three plus one is five. They are misdiagnosed by their teachers as stupid. It is just like colour blindness; it doesn't mean you are stupid."