New Study Shows It's More Than One, Two, Three For Rhesus Monkeys

(Washington, DC) --- Animals can not only be taught to count, but actually understand the concept of numbers according to new research published in the January issue of the Journal of Experimental Psychology: Animal Behavior Processes, published by the American Psychological Association.

Columbia University psychologists Elizabeth M. Brannon, Ph.D. and Herbert S. Terrace, Ph.D. designed experiments to discern whether monkeys could learn rules for putting objects into categories and then apply those rules to a new set of objects.

In their study, the researchers created computer displays with one, two, three, or four abstract elements such as circles, ellipses, squares, or diamonds of varying size and color. Three monkeys were then trained to touch each display in numerical order -two in ascending order, one in descending order. Overtime the monkeys were trained on 35 different displays. The researchers then tested the monkeys on 150 new displays and their performance did not falter.

However, in order to determine whether the monkeys understood the relationship between the numbers (e.g., that four is greater than three), the researchers tested the monkeys again, this time using pairs of numbers the monkeys had never seen before - five, six, seven, eight, and nine.

In the first round of testing with the higher numbers, both monkeys who had been trained to respond in ascending numerical order ordered the new numbers correctly 75 percent of the time. In subsequent tests, during which correct answers where positively reinforced, all three monkeys responded correctly at a level above chance guessing.

"This is the first instances where we're seeing expertise developing in monkeys," says Dr. Terrace. "The results of these experiments provide compelling evidence that number is a meaningful dimension for rhesus monkeys."

The researchers also point out that these monkeys were trained on their ordering skills for approximately six months and estimated that it takes children learning numbers thousands of repetitions to master similar concepts. The researchers also found several performance similarities between monkeys and people on similar tasks. For example, the monkeys are more accurate and quicker to order pairs of numbers the further apart the numbers are - in other words, ordering three and nine is easier then ordering three and four for both humans and monkeys.