Infants are not only known for responding to the voice of their parents, they also respond to the sound of non-human primates, according NBC News.
Human brains begin life hard-wired to hear the calls of non-human primates, an ability that fades away just after a few months.
Previous studies have shown that deep cognitive processes are set functioning as they listen to human speech.
Researchers found that sound from the blue-eyed Madagascar lemur engage their attentions too, in ways that artificial sounds don't.
"The link is sufficiently broad to include the call of this adorable lemur," Sandra Waxman, 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," she said.
Waxman explained that in the first months of childhood, "twin engines of development" - nature and nurture are at work.
Babies are born sensitive to primate sounds even from non-humans. As they get older, they no longer pay attention to the non-human sounds.It is human voices that stay relevant in their lives.
Waxman and colleagues studied how 72 infants aged three months and six 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, and similarly high-pitched lemur calls," said Waxman. They also heard human speech played backward and mechanical tones.
The difference was obvious. "They were doing some much fancier cognitive dancing during the lemur and human vocalization than in the case of backward speech or tones," Waxman elaborated.
Babies can't answer questions orally, 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.