The Associated Press Jan. 5 A chimpanzee has shown it can remember the correct sequence of five random numbers in an experiment that adds to the growing body of evidence that animals have some basic numerical ability. A female chimp tested with numbers between zero and nine performed about as well as an average pre-school child would, researchers at Kyoto University in Japan found. The chimp, named Ai, had already demonstrated that she could put five numbers in ascending order when they were scattered across a computer screen. But Kyoto researchers Nobuyuki Kawai and Tetsuro Matsuzawa reported in Thursday’s issue of the journal Nature that they took the experiment a step further.

Memorization Required When the chimp touched the first number, the four others were covered up behind small white squares on the screen. She then had to touch the squares in the proper order. Kawai and Matsuzawa said the chimp had to memorize all the numbers in order to make the right choices.      The chimp succeeded better than 90 percent of the time in identifying four numbers in the proper order, and was successful about 65 percent of the time with five items, far better than chance in each case.      Matsuzawa noted that in one testing session, Ai was distracted by a fight among other chimps outside the lab, but she returned to the screen and completed that particular trial without error.      The study builds on research by Herbert Terrace and Elizabeth Brannon at Columbia University in New York. They showed last year that rhesus monkeys could arrange pictures in order by the number of objects contained in the images. Evidence of Real Skills Brannon said, however, the Japanese research showed stronger evidence of mathematical skill.      “What’s interesting about this work is that they actually trained the chimpanzee to see the relationship between the symbol and the underlying number,” Brannon said. “It’s an extremely impressive task.”      The Kyoto researchers noted that pre-school children handle strings of five randomly ordered numbers fairly easily, but that increases only to about seven random numbers in adults.      Frans de Waal at the Yerkes Primate Center at Emory University in Atlanta said there is no clear evidence from field studies of chimpanzees that they use numbers in the wild. However, he said chimpanzees might use such a skill, for example, to count the number of predators they see. We're not 100 percent sure they are counting in the way that humans count, but we know that these animals can understand the relationship between numbers.” — Elizabeth Brannon, Columbia University Counting eight objects was a cinch for a pair of lab monkeys, but nine proved a bit too tough. It’s still better than most human toddlers can do and shows that animals can understand some basic numbers.      The rhesus monkeys, 2-year-olds Rosencrantz and Macduff, learned in a Columbia University lab to identify pictures of as many as nine objects and arrange the images in proper numerical order. Monkey Math It’s not quite the same as counting from one to nine, said Elizabeth M. Brannon, a graduate student and author of a study published today in the journal Science. But the research proves that animals have a rudimentary number sense, she said.      “We’re not 100 percent sure they are counting in the way that humans count, but we know that these animals can understand the relationship between numbers,” said Brannon. “For example, the animals do understand that seven is more than six. More generally, we think it’s really important evidence that number is a meaningful dimension for animals, that monkeys actually think about numbers.”      Previous studies by other researchers have shown some evidence of a number sense among pigeons, rats, ferrets, raccoons, dolphins and parrots.      But those may have only indicated that animals could differentiate, for instance, a pile of three peanuts from a pile of two peanuts, in the same way people can tell a cow apart from a tree. They could tell the two piles were different, but perhaps to them, “Is three greater than two?” was as much a nonsense question as “Is a cow greater than a tree?”

Rosencrantz, a 2-year-old rhesus monkey, takes the number test. (Columbia University) Not Just for People At one time, many scientists believed only humans could understand abstract numbers. “It’s results like these that are beginning to change people’s minds, ” said UCLA psychologist Randy Gallistel. The abstract notions of number and time, he said, “are turning out to be, on the contrary, deeply built into the fundamental structure of brains.”      Susan Carey, a New York University psychology professor, said this study demonstrates that rhesus monkeys can distinguish between sets of individuals on the basis of numbers, and that the animals could put the numbers in proper sequence.      She said it’s now clear that some animals do “have the capacity to represent numbers.”      The monkeys were almost error-free when comparing groups with up to eight objects, but faltered when challenged with nine. A Computer Game for Banana Candy The test devised by Brannon and co-author Herbert S. Terrace at Columbia required the monkeys to learn to properly sequence groups based on the number of objects pictured on a touch-sensitive video screen. The monkeys had to touch the right part of the screen to register their choices.      They first were shown four pictures that each contained different numbers, from one to four, of the same objects. These could be circles or squares or even flowers or rabbits.      “The monkeys learned to find the picture with one element, then the picture with two elements, and so on,” she said. To get a right answer, the animals had to touch the pictures in their proper numerical order, from one to four.      “A monkey learns by trial and error,” said Brannon. If the monkey punched all four pictures in the right order, he got a banana pellet. For a wrong answer, the screen went dark and the monkey had to wait until the next test. Many Variations To assure the animals were not simply memorizing pictures or making decisions based on size or position on the video screen, researchers used a number of different sets, including some the monkeys saw only once. The sets were randomly distributed on the video screen. Researchers also made sure the monkeys were not basing their choices on the objects’ size.      “In the number one picture, we might use a very large circle, while in the number four picture we use very tiny circles,” said Brannon. “This assures that the monkey is not just monitoring the size of the element.”      Once the monkeys had mastered the one-to-four sequence, they were then challenged to correct sequence pictures with five or more objects. This test was limited to only two pictures, mixed in with a series of pictures with one to four objects.      “The monkey might see five rectangles and six rectangles, with the five larger than the six,” said Brannon. “But the monkeys were still able to choose the five first. ”      There was no added training for the tests above the number four.      “We just sprinkled the higher numbers among the other numbers,” said Brannon. “We were testing whether they could infer” or apply what they had learned on smaller numbers to a similar test using larger numbers. And Then There Was Nine … Rosencrantz and Macduff did well until they got to the dreaded nines, said Brannon. But the results using the surprise introduction of higher numbers is important, she said, “because it shows that the monkeys know things about numbers that we haven’t taught them.”      Even though they have trouble with nines, Rosencrantz and Macduff still have “the number understanding of a 3- or 4-year-old human, and possibly even more advanced,” Brannon said.