Marmosets may be able to achieve levels of cognitive abstraction previously seen only in humans, chimpanzees and gorillas, according to a new study in APA's Journal of Comparative Psychology (Vol. 118, No. 2). The researchers tested the monkey's ability to mentally track the existence and movements of unseen objects, a skill termed "object permanence."
Biologist Ludwig Huber, PhD, and graduate student Natacha Mendes, of the University of Vienna's Institute of Zoology, set up a platform separated from a marmoset's cage by a glass barrier. Mendes then captured the animal's attention with its favorite breakfast cereal. She placed the food under one of three plastic boxes and then slid the barrier aside.
More often than not, the monkey found the food on the first try. While this "visible displacement task" may seem easy, many species of animals are not able to perform it, Huber says.
A second trial, an "invisible displacement task," was even more difficult. In it, Mendes placed the food in a cup and moved the cup underneath one of the boxes. Two of the 11 marmosets participating successfully followed the movement of the hidden food.
"This is really surprising," says Huber, "because before most people thought this [ability] would be restricted to humans and apes."
While most marmosets may not have the ability, attention span or motivation to follow the movement of invisible objects, a few outstanding individuals do, says Huber.
"This study also shows that there are big differences between individual animals, even if they belong to the same family group and have grown up in the same rearing conditions," he says.