The #1 source for news about monkeys and apes

[Carrie McLaren <stay.free AT verizon.net>]

June 06, 2005
http://sciam.com/print_version.cfm?articleID=00091022-CB1F-12A0 
-895D83414B7FFE87
Monkey Hear, Monkey Count
                
Rhesus monkeys possess a natural ability to match the number of voices  
they hear to the number of individuals they expect to see vocalizing,  
new research concludes. The results indicate that abstract  
representation of numbers is possible in the absence of language.

Writing in the June 7 Current Biology, Elizabeth Brannon of Duke  
University and her colleagues describe their experiment. The  
researchers played the monkeys "coo" calls made by either two or three  
unfamiliar conspecifics. They then let the monkeys watch their choice  
of video images showing either two or three animals. The vast majority  
of the monkeys selected video images that corresponded to the number of  
individuals heard on the audio sample. Each monkey was tested only once  
and did not receive a reward. This allowed the team to observe the  
animal's spontaneous behavior, as opposed to skills learned over the  
course of evaluation.

Brannon notes that in the wild, a monkey could conceivably hear various  
animals calling but not see them. "In a territorial dispute, you could  
imagine that an animal would want to know, 'Well, how many animals are  
really about to encroach on our territory?'"

"The results we obtained provide evidence that monkeys spontaneously  
detect a correspondence in number between two different sensory  
modalities, and this tells us that language is not necessary to  
represent number abstractly," Brannon comments. "When we humans apply  
the word 'three' to sounds or visual images, we're using language to  
link these different sets from different modalities. And the question  
has been whether an animal without that kind of language based  
representation can still notice or represent these commonalities."

If monkeys can manage such cross-modal representations of numbers, it  
seems probable that this ability was present in the last common  
ancestor of humans and monkeys. Future studies, according to team  
member Kerry Jordan, a graduate student in Brannon's lab, will take the  
same tack to determine whether humans have this capacity prior to  
learning language. --Kate Wong