The researchers, led by Elizabeth Brannon of Duke University and Asif Ghazanfar of Princeton University, published their findings in the June 7, 2005, issue of Current Biology. Brannon is in the Center for Cognitive Neuroscience and the Department of Psychological and Brain Sciences. Lead author on the paper was graduate student Kerry Jordan in Brannon's laboratory; and Nikos Logothetis of the Max Planck Institute for Biological Cybernetics in Germany was a co-author. The research was sponsored by The National Institute of Child Health and Development, the John Merck Fund, the Max Planck Society and a National Science Foundation graduate fellowship.
In their experiments, the researchers played rhesus monkeys the sound of natural "coo" calls made by unfamiliar monkeys, either with two or three animals making the calls. At the same time they gave the monkeys a choice to look at video images of either two or three monkeys. The researchers found that the monkeys overwhelmingly chose to look at video images that matched the number of monkeys they were hearing. This result is consistent with previous studies that both animals and infants tend to look preferentially at a visual stimulus that matches the sound they are hearing.
According to Brannon, previous studies had yielded conflicting results regarding whether perception of numerical values by nonhuman animals or human infants was tied to the sense used to perceive the number. To resolve the question, said Brannon, the researchers decided t