How Lemur Chatter is Proving to Help Infant Brain Development

The ability to link language to the world around us is a crowning feature of our species. For very young infants, it is not yet about learning the meaning of words like “cat” or “dog.” Rather, the acoustic signals in speech help foster infants' fundamental cognitive capacities, including the formation of categories of objects, such as cats or dogs.

The sounds that activate this key step in development can come not just from human language but also from vocalizations made by nonhuman primates. A new study shows that babies do not use just any natural sound to build cognition, however. While primate calls and human language pass the test, birdsongs do not.

By three or four months of age, infants can categorize objects—from toys and food to pets and people—based on commonalities those objects share. This ability is boosted if the objects are presented while the infants are listening to language.

The new findings build on previous work Waxman and her colleagues conducted about which sounds outside of the realm of human speech support infants’ ability to categorize objects. In past studies, they found that sequences of pure tones and backward speech do not help infants under six months of age to categorize objects, whereas listening to vocalizations from nonhuman primates—specifically, lemurs—does. Rather than incrementally investigate the breadth of sounds that babies respond to by testing their responses to various nonprimate mammals, the researchers decided to take a broader jump to a nonmammalian species.

Replicating the same categorization task used in past studies, the researchers showed 23 three- to four-month-olds eight images representing one of two categories—dinosaurs or fish—while simultaneously playing a zebra finch song. Next, in silence, they showed the infants two new images—one within the same category they previously viewed and one within the other category. Based on the previous work, the researchers knew that if the birdsong boosted the infants’ categorization, they would distinguish between the two test images. But in analyzing the infants’ gaze, the team found no difference in the amount of time the babies spent looking at either the familiar image or the new one. This indicated that the zebra finch song did not facilitate object categorization.