Primate calls, like human speech, can help infants form categories
A male mongoose lemur (Eulemur mongoz) Credit: Wikipedia
September 1, 2013
Human infants' responses to the vocalizations of non-human primates shed light on the developmental origin of a crucial link between human language and core cognitive capacities, a new study reports.
Previous studies have shown that even in infants too young to speak, listening to human speech supports core cognitive processes [ http://phys.org/tags/cognitive+processes/ ], including the formation of object categories.
Alissa Ferry, lead author and currently a postdoctoral fellow in the Language, Cognition and Development Lab at the Scuola Internationale Superiore di Studi Avanzati in Trieste, Italy, together with Northwestern University colleagues, documented that this link is initially broad enough to include the vocalizations of non-human primates.
"We found that for 3- and 4-month-old infants, non-human primate vocalizations promoted object categorization, mirroring exactly the effects of human speech, but that by six months, non-human primate vocalizations no longer had this effect—the link to cognition had been tuned specifically to human language," Ferry said.
In humans, language is the primary conduit for conveying our thoughts. The new findings document that for young infants, listening to the vocalizations of humans and non-human primates supports the fundamental cognitive [ http://phys.org/tags/cognitive/ ] process of categorization. From this broad beginning, the infant mind identifies which signals are part of their language and begins to systematically link these signals to meaning.
Furthermore, the researchers found that infants' response to non-human primate vocalizations at three and four months was not just due to the sounds' acoustic complexity, as infants who heard backward human speech [ http://phys.org/tags/human+speech/ ] segments failed to form object categories at any age.
Susan Hespos, co-author and associate professor of psychology at Northwestern said, "For me, the most stunning aspect of these findings is that an unfamiliar sound like a lemur [ http://phys.org/tags/lemur/ ] call confers precisely the same effect as human language for 3- and 4-month-old infants. More broadly, this finding implies that the origins of the link between language and categorization cannot be derived from learning alone."
"These results reveal that the link between language and object categories, evident as early as three months, derives from a broader template that initially encompasses vocalizations of human and non-human primates and is rapidly tuned specifically to human vocalizations," said Sandra Waxman, co-author and Louis W. Menk Professor of Psychology at Northwestern.
Waxman said these new results open the door to new research questions.
"Is this link sufficiently broad to include vocalizations beyond those of our closest genealogical cousins," asks Waxman, "or is it restricted to primates, whose vocalizations may be perceptually just close enough to our own to serve as early candidates for the platform on which human language [ http://phys.org/tags/human+language/ ] is launched?"
Say what? Human baby brains are wired to hear the call of the lemur
When human babies are 3 months old, they pay attention to lemur calls as well as human voices - but the attentiveness to a lemur call fades away by the time they're 6 months old. Sebastien Bozon / AFP / Getty Images
Nidhi Subbaraman, NBC News September 2, 2013
Infants respond to the voices of their doting parents — but it's not just human voices that hold them spellbound. In what may be a hallmark of our ancestry, human brains begin life hard-wired to hear the calls of non-human primates, an ability that fades away after just a few months.
Past studies with infants have shown that deep cognitive wheels are set turning as they listen to human speech. Now researchers have found that sounds from the blue-eyed Madagascar lemur engage their attention, too, in ways that artificial sounds don't.
"The link is sufficiently broad to include the call of this adorable lemur," Sandra Waxman [ http://www.wcas.northwestern.edu/psych/people/faculty/faculty_individual_pages/Waxman.htm ], professor of cognitive psychology at Northwestern University and a co-author on the new study, told NBC News. "The fact that there's this precocious link between language and thought ... it's just hands-down amazing."
In the first months of childhood, "twin engines of development" — nature and nurture — are at work, Waxman explained. Babies are born sensitive to primate sounds, even from non-humans. When they grow older, they no longer pay attention to the non-human sounds. It's the human voices that stay relevant in their lives.
'Candy to a baby's ears'
Waxman and colleagues studied how 72 infants between the ages of 3 months and 6 months responded to human, lemur and artificial sounds. The babies listened to high-pitched baby talk — "It's like candy to a baby's ears," Waxman said — and similarly high-pitched lemur calls. They also heard human speech played backward, and mechanical tones.
The difference was clear. "They were doing some much fancier cognitive dancing during the lemur and human vocalization than in the case of backward speech or tones," Waxman explained.
Babies can't answer questions verbally, and it will be years before they can fill out multiple-choice surveys. So for psychologists, the gaze of babies — where they look, and for how long — is a tried-and-true way of indicating whether they're engaged.
A 3-month-old at Sandra Waxman's lab at Northwestern University gazes at a blue dinosaur projected on the screen (inset) in front of her. Project on Child Development/Sandra Waxman/Northwestern University
In the tests conducted by Waxman and her colleagues, 3- and 4-month-olds were shown a series of eight similar shapes — all dinosaurs — projected on a screen in front of them. In the background, one of the four kinds of sounds would play on a loop. Then they were shown an image of a ninth dinosaur, placed next to a dissimilar image shaped like a fish.
"If the baby has noticed what's common about the objects, they're going to prefer this as one over the other," Waxman explained.
The babies who were trained on the first eight images while they listened to the speech played backward or the mechanical tones didn't master the categorization task as easily as they did when they heard the human or lemur sounds. That indicates that the babies were less engaged in the task while they were listening to the artificial sounds.
The babies who were 6 months old exhibited a different trend: They seemed receptive to the human voices, but not to the lemur calls. That suggests that they lost their sensitivity to the non-human primate sounds because they were hearing human voices all the time.
Having established that babies can be sensitive to the lemur sounds, Waxman and her colleagues are working on refining their understanding of the qualities of lemur calls and human voices that attract an infant's attention, and finding out what other kinds of sounds — primate or otherwise — can bring out a similar response.
Meanwhile, a second study at Waxman's lab is investigating whether babies can retain their ability to engage with lemur calls and human voices, if their parents play them the lemur calls at bedtime every day.
Alissa Ferry, Susan Hespos and Sandra Waxman are authors of "Nonhuman Primate Vocalizations Support Categorization in Very Young Human Infants [ http://www.pnas.org/cgi/doi/10.1073/pnas.1221166110 ]," published in the Proceedings of the National Academy of Sciences.
as teaching aids. The findings hint at a deep biological connection between language and learning.
Babies begin learning as soon as they're born. They're listening too. But researchers still don't know exactly how the development of language and learning are linked: "How do language and concepts come together in the mind of the baby?" asks Sandy Waxman [ http://www.wcas.northwestern.edu/psych/people/faculty/faculty_individual_pages/Waxman.htm ], a psychologist at Northwestern University in Evanston, Illinois.
Waxman has devoted her career to answering that fundamental question. She says the language-learning connection is clear in older children. For example, a 2-year-old hears the word "dinosaur" when she sees many different kinds of dinosaurs. She soon connects the word "dinosaur" to the dinosaur category, and she can more easily identify future dinosaurs when she sees them.
But much younger children can't clearly discern words; can language still help them to learn categories? Waxman's previous work suggested it might. In her earlier study, 3-month-old babies were played human speech segments while they stared at a screen displaying dinosaurs. Later they were shown new dinosaurs. By watching their eyes, the scientists could see that infants could recognize other dinosaurs better when they had been taught the category while the human speech was playing in the background.
But was it really the speech that got their attention, or just the sound that intrigued them? Waxman needed an answer, so this time she and her team tried to teach babies categories while they listened to two different sounds: the shriek of a lemur and human speech run backwards.
"We reasoned that if the language effect that we'd seen earlier was nothing more than an infant's response to the complexity of the auditory signal, than both of those new sounds should help them form categories at this very early stage," she says.
In other words, if the sound was just a way of getting their attention, the babies would learn to categorize equally well while listening to both lemur shrieks and backwards speech.
But that's not what the researchers found. The backwards speech didn't help the babies to learn categories at all. But the lemur shrieks did. The study appears in this week's issue of the Proceedings of the National Academy of Sciences [ http://www.pnas.org/cgi/doi/10.1073/pnas.1221166110 ].
"This work shows a very fundamental link between language and learning," says Janet Werker [ http://www.psych.ubc.ca/faculty/profile/index.psy?fullname=Werker,%20Janet&area=Developmental&designation=core ], who studies the roots of language acquisition at the University of British Columbia in Canada. Werker says that the new study shows that there is something unique about the sounds we and our nearest animal relatives make. Even if little babies can't pick out the words, the sounds say, 'Pay attention, you just might learn something!' "
But not everyone agrees that the new work shows that primate sounds can stimulate a child's linguistic instinct. "This work tells us that sounds that are more like human language are more effective," says Lisa Oakes [ http://mindbrain.ucdavis.edu/people/lmoakes ], a psychologist at the University of California, Davis. "What is more controversial is why they are effective." She says it's still not clear whether the primate sounds are stimulating some deep linguistic circuit in the brain, or just getting the babies to look.
Whatever the effect, it doesn't last for long. By the time they were 6-months-old, the babies had tuned out the lemur cries. Only human speech played forward helped them to learn then.
Should Shots readers with 3-month-olds leave their babies in the care of a lemur teacher?
"It would be a fantastic experiment but I wouldn't endorse it," Waxman says. "I mean you know what lemurs are like. You wouldn't want to leave your baby alone with one of them."
Sharing childcare duties help lemur babies survive, Yale researchers find
By Bill Hathaway 06/08/2013 21:53:00
Some lemur mothers, like their human counterparts, share child-rearing responsibilities and tend to fare better than lemur moms that go it alone, Yale University researchers have found.
Black-and-white ruffed lemurs which share nests with other mothers have more time to forage for food according to the study published Aug. 6 in the journal Behavioral Ecology and Sociobiology.
“Mothers that cooperate have more time to eat and take care of themselves and, in turn, their offspring are more likely to survive,” said Brenda Bradley, assistant professor of anthropology and co-author of the study.
Ruffed lemurs and humans are the only day-active primates known to use ‘kindergartens,’ or pooling of infants by multiple mothers. The ruffed lemurs of Madagascar are also unusual among primates because they are born in litters and give birth only once every few years. Like human babies, the lemurs are undeveloped at birth and totally dependent upon their mothers. In the weeks leading up to birth, black-and-white ruffed lemur mothers build nests in trees like birds.
“And some mothers — but not all — end up moving in and creating communal nests to cooperatively raise offspring,” said Andrea Baden, post doctoral researcher and first author of the study. “While two or three mothers are off fulfilling other needs, like foraging and socializing, one will stay behind to babysit and protect infants in the nest, including those that are not her own.”
Yale researchers not only observed lemur behavior in the wild but conducted genetic tests on the lemurs to determine whether the nest sharers were related and simply creating a sort of family compound. Intriguingly, non-relatives and kin both share nests.
Baden would like to study why some mothers chose to raise children alone if there were clear advantages to raising offspring communally.
“It is unclear why some females cooperate and others do not,” Baden said.
Work was funded by: National Science Foundation, LSB Leakey Foundation, J William Fulbright Foundation, Primate Conservation Inc., Conservation International, Stony Brook University, Omaha’s Henry Doorly Zoo, and Yale University.
Other authors were: Patricia Wright, Stony Brook University, and Edward E. Louis Jr., Omaha’s Henry Doorly Zoo.
News 
Market Data 
Discover 
