SHANKAR VEDANTAM, HOST: Hey, Shankar here. I\u2019ve always wanted to share interesting things that don\u2019t make it onto the show and to hear directly from you. Now there\u2019s a way to connect one on one - my newsletter. You can subscribe at news.hiddenbrain.org. That address again is news.hiddenbrain.org. See you soon.(SOUNDBITE OF ARCHIVED NPR BROADCAST)VEDANTAM: This is HIDDEN BRAIN. I'm Shankar Vedantam. There's a video on YouTube you might have seen. It has nearly 200 million views. In this video, a pair of twin brothers are standing in a kitchen having a little chat.(SOUNDBITE OF YOUTUBE VIDEO)UNIDENTIFIED INFANTS: (Babbling).VEDANTAM: These twin brothers...(SOUNDBITE OF YOUTUBE VIDEO)UNIDENTIFIED INFANTS: (Babbling).VEDANTAM: ...Are diaper-clad babies. Now, if this video featured 10-year-old twins or adult twins, I guarantee you it wouldn't have gone viral. What makes this video special is that we have no clue what these babies are saying. To us non-babies, it sounds like gobbledygook - cute, mysterious gobbledygook.(SOUNDBITE OF YOUTUBE VIDEO)UNIDENTIFIED INFANTS: (Babbling).VEDANTAM: Here at HIDDEN BRAIN, we love trying to understand the puzzles and contradictions of human behavior, but we spend most of our time talking about the older members of the human race. Today, we focus on the younger set - the much younger set.LAURA CIRELLI: I find babies are so impressive. We can't really ask them what they're thinking. We have to come up with clever ways of figuring out what's going on in their little brains.VEDANTAM: We'll meet some of the researchers trying to decipher the behavior of babies.RACHEL ALBERT: Oh, oh, you're - oh, that's a ball. Yeah, you're right.VEDANTAM: Do babies understand us when we're talking to them?ALBERT: That's a ball. You tried to say ball. That's great.VEDANTAM: And how babies communicate even if they don't have words.(SOUNDBITE OF YOUTUBE VIDEO)UNIDENTIFIED INFANTS: (Babbling).VEDANTAM: The language of babies this week on HIDDEN BRAIN.(SOUNDBITE OF MUSIC)CIRELLI: Hi, I'm Laura Cirelli.VEDANTAM: When Laura was in college, she spent her summer vacations back home in Sudbury, Ontario.CIRELLI: Like, five hours north of Toronto.VEDANTAM: And she worked at the Magical Nook, a day care center.CIRELLI: It was a large center that had different age groups, so there was, like, a baby room and a toddler room, preschoolers, school-age children. Probably about a hundred children in total, but my favorite room was the toddler room for sure.VEDANTAM: Laura's job was to help the teachers at the center engage with the kids and enforce the rules.(SOUNDBITE OF MUSIC)VEDANTAM: Music was an essential tool.CIRELLI: We would sing "Wheels On The Bus..."(SOUNDBITE OF SONG, "WHEELS ON THE BUS")UNIDENTIFIED SINGERS: (Singing) The wheels on the bus go round and round.CIRELLI: "...Old MacDonald..."(SOUNDBITE OF SONG, "OLD MACDONALD HAD A FARM")UNIDENTIFIED SINGER: (Singing) Old MacDonald had a farm, E-I-E-I-O.CIRELLI: If we didn't sing the clean up song with the preschoolers, then I don't think anything would have ever gotten cleaned up.(SOUNDBITE OF TV SHOW, "BARNEY AND FRIENDS")UNIDENTIFIED ACTORS: (As characters, singing) Clean up, clean up, everybody everywhere.CIRELLI: But as soon as we started, it seemed to be the trick to convince them that, yes, they were willing to put their toys away.(SOUNDBITE OF TV SHOW, "BARNEY AND FRIENDS")UNIDENTIFIED ACTOR: (As Baby Bop) Such a mess.VEDANTAM: Laura regularly found herself in awe of the toddlers.CIRELLI: One little kid who I had a good connection with, she grabbed my hand and brought me over to the little slide, and she really wanted to go down the slide. You could tell. So I helped her up the little stairs, and I caught her at the bottom of the slide. And all the rest of the toddlers in this playground just looked over and saw her and looked at each other and then ran over to the slide and formed a cute little lineup waiting their turn for me to help them down.(SOUNDBITE OF MUSIC)VEDANTAM: Laura's days are the Magical Nook are now over. After graduating college, she went on to earn her Ph.D. in psychology, neuroscience and behavior. She is now a professor at the University of Toronto Scarborough, and her work focuses on early childhood development. With years of knowledge now under her belt, she looks back on that moment at the slide and sees it as a form of communication.CIRELLI: You know, in order for kids to look around and see what their peers are doing and to understand the goals that are embedded in those activities and to then realize that they need to follow the social construct of lining up, it seems like a super simple thing, but there's a lot of understanding about themselves, about other people, about goals and activities that they need to really completely understand in order for that to happen.VEDANTAM: Laura says actions like standing in line for the slide can be categorized as prosocial behaviors. They're actions we take to help others and to benefit the group. She decided to study what she'd seen on the playground more systematically. She invited a bunch of parents to bring their toddlers into the lab.CIRELLI: We were specifically testing 14-month-old babies. So they're - you know, they're walking. They're not quite talking.VEDANTAM: These 14-month-olds said bye-bye to Mommy and Daddy and then were strapped into front-facing baby carriers worn by assistants in the study. The researchers turned on some music.CIRELLI: Usually, it was "Twist And Shout" playing the background.(SOUNDBITE OF BEATLES SONG, "TWIST AND SHOUT")VEDANTAM: And the person carrying the baby began to bounce.CIRELLI: It was like (rhythmic clapping) so we would bounce them down on one beat and up on the other, down and up sort of thing.VEDANTAM: So if you're this baby, you're strapped onto someone's chest, you can't see their face. Instead, you're looking in front of you at another assistant.CIRELLI: The person facing the baby would either move in synchrony with how they were being bounced, so they're bouncing together, or they would move either too quickly or too slowly so that their movements weren't aligned with what the baby was experiencing.VEDANTAM: After about 2 1/2 minutes, the bouncing stopped and the baby was removed from the carrier.CIRELLI: And then this person who had faced them and moved either in or out of sync with them would perform some little, simple social games with them. So she would do things like draw pictures with markers or throw paper balls in a bucket.VEDANTAM: Every now and then, the assistant who had faced the baby would drop a marker or paper ball and then pretend like the object was out of reach.CIRELLI: So she would reach pathetically for them for about 30 seconds and we'd look to see what the babies did in this really weird situation where this person they just met needs help but isn't really asking for help and doesn't really seem to be able to achieve their goal on their own.VEDANTAM: Laura measured how many babies would pick up and hand back the objects.CIRELLI: And looked at whether the babies who we bounced in sync with helped at a different rate than the babies we bounced out of sync with.VEDANTAM: She found that babies who felt that they were bouncing in sync with a dance partner were more likely to help that partner pick up an object when it was out of reach. It was remarkable.CIRELLI: So they would help on over half of the trials if we moved in sync with them, whereas if we moved out of sync with them, they would help on only less than a third of the trials.(SOUNDBITE OF MUSIC)VEDANTAM: You've likely experienced the same drive if you've ever moved in sync with someone else, maybe on a sports team in school or in marching band or maybe, like Laura, as a dancer.(SOUNDBITE OF FILM, "BEAUTY AND THE BEAST")JERRY ORBACH: (As Lumiere, singing) Be our guest, be our guest, put our service to the test. Tie your napkin 'round your neck, cherie, and we'll provide the rest.VEDANTAM: This song was a soundtrack of Laura's last recital in high school where she dressed up as Mrs. Potts for a performance of "Beauty And The Beast."CIRELLI: There were many numbers in the performance, but in the "Be Our Guest" performance, everyone comes together, all the little kitchen utensils and everything, and we do have to really synchronize at certain parts of the dance. And so when you're experiencing that, you really feel like you're part of this bigger group. And, I mean, you're focusing on the task at hand, you know, doing all of these steps, but that's become quite automatic at this point. And instead, you can really sort of feel the connection with your co-dancers, and you start to just ignore the audience completely because you're part of this bigger thing.(SOUNDBITE OF FILM, "BEAUTY AND THE BEAST")UNIDENTIFIED ACTORS: (As characters, singing) Come on and lift your glass. You've won your own free pass to be our guest.ORBACH: (As Lumiere) If you're stressed...VEDANTAM: Laura's fellow dancers remain some of her closest friends to this day.CIRELLI: I'm going to be the emcee at one of their weddings in September (laughter). So yeah, we've definitely stayed very close.VEDANTAM: Music and dance create bonds because, as Laura says, synchronous movement is a language of its own. This unspoken language can guide behavior even though many of us are not familiar with its syntax and vocabulary.CIRELLI: I think music is providing a really interesting context where a lot of social cues are happening. So when we're moving with other people, when we're doing familiar things and singing familiar songs, these are actually cueing us, babies and adults, to think about the relationships that we have with these people.(SOUNDBITE OF MUSIC)CIRELLI: We think about teaching our kids to be prosocial and to be good citizens, but they're already attending to this information from a really early age.VEDANTAM: The toddler experiment also shows that kids who can't speak are still hungry to communicate. When a small child reaches out to pick up a marker or a paper ball, she may be saying, I like you. I want to help you. Let's be friends.(SOUNDBITE OF MUSIC)CIRELLI: I find babies are so impressive. We can't really ask them what they're thinking. We have to come up with clever ways of figuring out what's going on in their little brains, and everybody underestimates them.VEDANTAM: Music and dance aren't the only ways adults and small kids communicate with one another. There's another language that actually sounds a lot like language.UNIDENTIFIED INFANTS: (Babbling).ALBERT: The traditional way of looking at babbling, even as recently as 15, 20 years ago, was really that it was just motor practice, that it had no bearing on later language. It was just something babies did to exercise their mouths.VEDANTAM: This is Rachel Albert.ALBERT: I am an assistant professor of psychology at Lebanon Valley College in Annville, Pa.VEDANTAM: She studies infant language development. Those, quote-unquote, "traditional views on babbling..."UNIDENTIFIED INFANT: (Babbling).VEDANTAM: ...Rachel says toss them out.ALBERT: When babies babble, they're indicating that they're either in a heightened state of arousal or by actually babbling they're increasing their arousal level and putting themselves in kind of this optimal state of being ready to learn over and above than if they were just quietly looking at an object.VEDANTAM: Rachel says babbles have a certain je ne sais quoi.UNIDENTIFIED PERSON: (Speaking French).VEDANTAM: When she hears a baby babble, she's taken back to high school French class.ALBERT: And I had one of those immersive French teachers who would only speak French in the classroom. And so it was really like being dropped into a non-native environment where you have to kind of figure things out. I vividly remember that she would come into the classroom, and she would start talking and...UNIDENTIFIED PERSON: (Speaking French).ALBERT: ...The whole class would kind of have blank stares of panic as she would go. And so she'd start slowing down her speech...UNIDENTIFIED PERSON: (Speaking French).ALBERT: ...And pointing and labeling particular objects in the room.UNIDENTIFIED PERSON: (Speaking French).ALBERT: So she would, in French, be kind of pointing and saying, you know, are you sitting in a desk?UNIDENTIFIED PERSON: (Speaking French).ALBERT: Look at the desk. Here's a desk...UNIDENTIFIED PERSON: (Speaking French).ALBERT: ...And kind of repeating those key vocabulary words until we started to figure out, oh, OK, this is the word for desk.UNIDENTIFIED PERSON: (Speaking French).ALBERT: And I thought, well, this must be somewhat similar to what a baby experiences - right? - where there's all this conversation going around.UNIDENTIFIED PEOPLE: Blah, blah, blah, blah, blah, blah.ALBERT: They start to become active communication partners and trying to engage in that world, but how do they make sense of it?UNIDENTIFIED INFANT: (Babbling).VEDANTAM: Parent's often see themselves as the know-it-all French teacher and the babbling baby as a clumsy student. Rachel says this framework is the one that's mostly used in studying infant language development.ALBERT: But the baby is playing as much of a role in this interaction as the mom. By changing the way that they babble and what they're looking at - might actually be changing their opportunities for learning because they're changing what the parents say. It's kind of what we call a social feedback loop. So when the baby babbles, Mom responds. The way Mom responds actually will change in real time what the child says next. And they go around and around in this conversation influencing each other.(SOUNDBITE OF MUSIC)VEDANTAM: There's a word to describe a back-and-forth exchange where the thing that one person says affects what another person says. This feedback loop of communication and learning is what we call language.(SOUNDBITE OF INFANT VOCALIZING)VEDANTAM: Babies make as many as a thousand vocalizations every day. On average, parents respond to about 60% of these babbles.ALBERT: Even just silently responding - if the mom just acknowledges the infant's vocalization with a touch - leans in, smiles and touches the baby - the infant will immediately, within the span of just 10 minutes, start to produce more speech-like vocalizations. So just that nonverbal feedback, that acknowledgement of the baby's vocalization, changes in the moment how they're babbling.VEDANTAM: Rachel says that when babies are babbling, they are more receptive to new information. Parents can take advantage of this by having conversations with their baby. And one rule of being a good conversationalist - stay attentive to what your partner is saying.ALBERT: So parents that are just talking constantly about irrelevant things that aren't what their child's looking at - for example, if a baby is looking at a ball and I'm talking about this cup over here that I'm playing with - well, you're actually providing mismatching communication - mismatching information for them that's going to make it harder to learn.VEDANTAM: Rachel says if you listen closely, babbling often falls into four distinct categories. They have different sounds, and they elicit different responses.(SOUNDBITE OF INFANT COOING)VEDANTAM: The first type is called...(SOUNDBITE OF INFANT VOCALIZING)VEDANTAM: ...QRVALBERT: QRV is the least mature infant vocalizations. It stands for quasi-resonant vocalization. And so it's those really kind of nasal, creaky ehh (ph) kind of - sounds that a lot of times parents interpret almost as fussing.VEDANTAM: The second type is called...(SOUNDBITE OF INFANT VOCALIZING)VEDANTAM: ...FRV.(SOUNDBITE OF INFANT VOCALIZING)ALBERT: So that's a fully resonant vowel. And around 3 or 4 months, the baby's vocal tract opens up. And then they're able to produce those more open, kind of adult-like sounding vowels that kind of have those ohs or ah quality. And so parents recognize those as more speech-like than those first, creaky nasalized vowels. And so they're more likely to respond to those.VEDANTAM: The third is called...(SOUNDBITE OF INFANT VOCALIZING)VEDANTAM: ...MSFR.(SOUNDBITE OF INFANT VOCALIZING)ALBERT: So that's a marginal syllable. And babies will start, around 6 or so months, throwing consonants into the mix. So you can hear in that sound, there's kind of a D-J kind of juh (ph) sound.(SOUNDBITE OF INFANT VOCALIZING)ALBERT: But it's a slow, drawn-out transition between when the consonant stops and when the vowel begins.VEDANTAM: And the pinnacle...(SOUNDBITE OF INFANT VOCALIZING)VEDANTAM: ...The piece de resistance if you will...(SOUNDBITE OF INFANT VOCALIZING)ALBERT: So that's what's called a canonical syllable. And those are those nice ba-bas (ph) and da-das (ph) that parents naturally associate with babbling. And so babies start regularly producing those pretty frequently around 9 months. And parents react very strongly to these canonical syllables. They hear them as the most speech-like. They tend to often interpret them as approximations of words. So, you know, in that example, if a baby was holding a ball...(SOUNDBITE OF INFANT VOCALIZING)ALBERT: ...A mom would be very likely to respond - oh, you - oh, that's a ball. Yeah, you're right. That's a ball. You tried to say ball. That's great.VEDANTAM: To Rachel, these different vocalizations are endlessly fascinating. Now that she knows how to tell apart the QRVs...(SOUNDBITE OF INFANT VOCALIZING)VEDANTAM: ...From the FRVs...(SOUNDBITE OF INFANT VOCALIZING)VEDANTAM: ...And the MSFRs...(SOUNDBITE OF INFANT VOCALIZING)VEDANTAM: ...From the canonical syllables...(SOUNDBITE OF INFANT VOCALIZING)VEDANTAM: ...She simply can't stop herself.ALBERT: On my wedding day, I remember very distinctly - I was in graduate school at the time and knee-deep in coding this all the time, spending hours listening to these different sounds. And I remember being up at the front of the church about to say my vows and hearing some babies out in the audience babble and kind of immediately coding it and going - oh, that was a marginal syllable. And then thinking - no, focus. This is a very important moment. You're supposed to be attending to what your pastor is saying. But I couldn't help but have my attention pulled by the baby in the audience and trying to code what she was saying.(SOUNDBITE OF INFANTS VOCALIZING)VEDANTAM: You don't have to memorize all the jargon to take away something valuable from the research. Just knowing that when babies are babbling, they're ready to learn - that can be a useful takeaway for everyone.(SOUNDBITE OF MUSIC)VEDANTAM: When we return, we discuss two final elements of baby language. One is going to make you very happy. The other - well, that's something you don't want to hear as you're saying your wedding vows.(SOUNDBITE OF VIDEO)KATRINA DOUDNA: (Screaming) No.(SOUNDBITE OF MUSIC)VEDANTAM: A warning - if you're driving or listening to this story as you're cooking, you're about to hear something very distracting.(SOUNDBITE OF VIDEO)KATRINA: (Screaming) No. No.VEDANTAM: This is Katrina Doudna of Sunnyvale, Calif. It's dinnertime. She's throwing a tantrum because she wants to sit at the head of the table.(SOUNDBITE OF VIDEO)KATRINA: (Screaming).VEDANTAM: Problem is the table's round. There is no head.NOEMI DOUDNA: When she was in the midst of a tantrum, she'd picked something that she knew was completely unreasonable. (Imitating tantrum) I don't want my feet. Take my feet off. I don't want my feet. I don't want my feet.VEDANTAM: That's Katrina's mom, Noemi. I interviewed her a number of years ago when Katrina was 3.N DOUDNA: I once teased her - which turned out to be a big mistake. But I once said, well, OK - let's go get some scissors and take care of your feet. (Imitating tantrum) No.(SOUNDBITE OF MUSIC)MIKE POTEGAL: My curiosity was focused on what are the elements of the tantrums? You know, are the snips and snails and puppy-dog tails or what?VEDANTAM: This is Mike.POTEGAL: It's Mike Potegal. I am currently an associate professor in the Program in Occupational Therapy at University of Minnesota.VEDANTAM: Mike was inspired to study tantrums after witnessing his own daughter's operatic meltdowns.POTEGAL: Among the things that I learned from that was that there was a sequence in which various behaviors appeared, various behaviors of which tantrums are composed.VEDANTAM: Just like Rachel Albert did with babbling, Mike picked out a rhythm in a cacophony of his daughter's tantrums. To prove his point, he teamed up with a colleague...JAMES GREEN: James Green.VEDANTAM: He's a psychologist at the University of Connecticut.GREEN: We developed a onesie that toddlers can wear that has a high-quality wireless microphone sewn into it. Parents put this onesie on the child and press a go button on the equipment.VEDANTAM: And then they waited for a meltdown. James and Mike recorded more than a hundred of them. And what they found confirmed their hypothesis.POTEGAL: There are two major - I think of them as emotional behavioral components of tantrums.VEDANTAM: The first is anger.POTEGAL: Hitting, kicking, screaming, throwing things, pushing and pulling.VEDANTAM: And the other component is distress.POTEGAL: Whining, crying, throwing the self down - that is, dropping to the floor - and comfort-seeking.VEDANTAM: Don't confuse these components with stages. Mike says the behaviors occur simultaneously. The distress is more consistent.POTEGAL: Throughout the tantrum, from its beginning to its end.VEDANTAM: The anger punctuates the tantrum. It provides the dramatic spikes, and it also tapers toward the end.POTEGAL: In every case, the anger terminates before the distress.VEDANTAM: Mike says there's a reason that most tantrums end with a distress call.POTEGAL: Because the distress, sadness, tends to elicit comfort-giving. And so it would make sense from an evolutionary perspective if the anger, which is disruptive, is smoothed over by the distress component which then, other things equal, will call for a parent comforting the child.VEDANTAM: Let's go back to Katrina, the child who was throwing a fit because she can't sit at the head of the family's circular dinner table.(SOUNDBITE OF VIDEO)KATRINA: (Screaming) No. No.VEDANTAM: Dad tries to reason with her.(SOUNDBITE OF VIDEO)DAVID DOUDNA: Do you want to sit at? Do you want to sit - do you know what? It doesn't have corner 'cause it's round. It's a circle.KATRINA: (Screaming).VEDANTAM: James Green says that he's fallen into the same trap before.GREEN: When children are at the peak of anger and they're screaming and they're kicking, probably asking questions might prolong that period of anger.(SOUNDBITE OF VIDEO)KATRINA: (Screaming).VEDANTAM: Dad decides to intervene.(SOUNDBITE OF VIDEO)D DOUDNA: I'm going to pick this chair for you.KATRINA: (Screaming) No, no. No.VEDANTAM: Now Katrina is on the floor. She grabs a stool and...(SOUNDBITE OF VIDEO)VEDANTAM: ...Slams it against the wall.(SOUNDBITE OF VIDEO)KATRINA: (Screaming).VEDANTAM: It seems like things are escalating, but James says it's just the opposite.GREEN: Once she's thrown herself on the floor and thrown something or, in this case, knocked the chair against the wall, we're probably on the down slope of this tantrum. She's spent a lot of energy screaming, yelling and now doing these physical behaviors.VEDANTAM: Listen to Katrina. And pay attention to how the register of her voice changes.(SOUNDBITE OF VIDEO)KATRINA: (Screaming) No. (Sobbing) No. (Screaming) No.VEDANTAM: Mike says, in many cases, parents can safely ignore their child's tantrums.POTEGAL: And this approach has a formal name - planned ignoring. And it basically means turning your back on the child and walking out of the room because talking to them and telling them to stop is giving them attention, albeit negative attention.VEDANTAM: This works best when the child throws a tantrum to get attention or because you've said no to eating cookies at dinner. But if the child throws a tantrum in response to something you asked them to do...POTEGAL: A very different approach is appropriate. And the reason for that is that what the tantrum does is basically a stall. It's a way for the child to not comply with the parent request. And so the best approach, if it can be managed, is to get the child to comply with the request. For younger children, this can be done with a hand-over-hand kind of forced cooperation. So you can say to the child, OK, get your PJs on. And if the child refuses, you can say - OK, I'm going to count to three or five or whatever you like. And if you have not begun putting your PJs on I'm going to put my hands on your hands and help you do it. And children really do not like this.VEDANTAM: Because, he says, it's a threat to their autonomy. And if the child still doesn't comply, maybe you can use it as an opportunity to do some research, just like Mike.POTEGAL: We would walk down the street. And I'd see a kid having a tantrum. And I would say - I would mutter or say out loud to my wife, data. And then of course she'd give me a sidelong look about (laughter) what's wrong with you (laughter)?(SOUNDBITE OF MUSIC)VEDANTAM: We've talked so far about the secret languages of dancing and babbling. We've looked at the grammar of temper tantrums. We're getting close to the end of our story, and that brings us to lullabies.(SOUNDBITE OF MUSIC)VEDANTAM: Laura Cirelli, the first researcher we featured on dancing and synchronization, has also done work on the language of music with infants.CIRELLI: Across cultures, we all engage with music, and we do it at such an early age, so we really wanted to continue to explore this idea that one of the real benefits and perhaps one of the underlying reasons why we invest so much time and energy in music across cultures is because of these social and emotional implications.VEDANTAM: Remember the magic of the clean up song that Laura talked about earlier? She and her fellow researchers wanted to closely examine the effect of music on babies and their caregivers. They asked parents to volunteer to come into the lab with their babies. Thirty mothers said they would do it.CIRELLI: They would be in a soundproof room, and babies would be sat in a little highchair, and moms would sit facing them.VEDANTAM: They were also measuring stress levels.CIRELLI: So we used little stickers on the bottom of the baby's foot and on the mother's fingertips, and we were - what we're able to measure with this is actually their sweat gland activity.VEDANTAM: The mothers then sang two versions of "Twinkle, Twinkle Little Star." One version...(SOUNDBITE OF SONG, "TWINKLE, TWINKLE LITTLE STAR")UNIDENTIFIED SINGER: (Singing) Twinkle, twinkle little star.VEDANTAM: ...Was upbeat.(SOUNDBITE OF SONG, "TWINKLE, TWINKLE LITTLE STAR")UNIDENTIFIED SINGER: (Singing) How I wonder what you are.VEDANTAM: The other...(SOUNDBITE OF SONG, "TWINKLE, TWINKLE LITTLE STAR")UNIDENTIFIED SINGER: (Singing) Twinkle, twinkle little star.VEDANTAM: ...Was a lullaby.(SOUNDBITE OF SONG, "TWINKLE, TWINKLE LITTLE STAR")UNIDENTIFIED SINGER: (Singing) How I wonder what you are.CIRELLI: What we found was that when Mom sang in a playful way, the - both Mom and baby's arousal levels stayed stable. But when Mom sang in a soothing way...(SOUNDBITE OF SONG, "TWINKLE, TWINKLE LITTLE STAR")UNIDENTIFIED SINGER: (Singing) Twinkle, twinkle little star.CIRELLI: ...Both mom and baby's arousal levels decreased as the song progressed. So what this is telling us is that lullabies are really working to calm not only baby but also the mother. And so this supports this idea that there's a function here.VEDANTAM: Is this telling us just what our - is this just confirming what our intuitions are telling us or do you think it's telling us something more than that?CIRELLI: Anecdotally, I'm sure most parents would agree that lullabies soothe their babies. But usually, when we're singing lullabies to our babies, we're holding them and we're rocking them and we're adding all of this really important soothing tactile information. So we wanted to know what the song is doing, removing all of that tactile input.(SOUNDBITE OF MUSIC)CIRELLI: So the babies are sitting in a highchair. They're facing their mom, but they're not experiencing that holding and that rocking that typically comes along with lullabies. But I think the really interesting thing here is we usually think of that unidirectional relationship. Like, when moms sing to babies, it is to change the baby's behavior. But I think it's - the really new, interesting thing here is considering how it's also affecting the mom.VEDANTAM: Indeed, if there's one thing that all this research shows, it's that communicating with babies is not a one-way street. Parents and caregivers are shaped by what babies say and sing and scream, just as babies are hungrily soaking up information from adults. When we think about raising a human, it's natural that most of us think about the role that adults play in shaping their children. What's less clear - but what is abundantly true - is that babies are every bit as involved in raising humans of their own. It's not just a figure of speech. We're all always growing up.(SOUNDBITE OF MUSIC)VEDANTAM: This week's show was produced by Parth Shah and was edited by Tara Boyle. Our team includes Rhaina Cohen, Jenny Schmidt, Thomas Lu and Laura Kwerel.We like to end our podcast by acknowledging an unsung hero, a person behind the scenes who helps us create the show. Today, we want to recognize the mothers and fathers of the HIDDEN BRAIN team - Vatsala (ph), Lakshmiputhi (ph), Melanie (ph), Steve (ph), Dorothea (ph), Steven (ph), Comlesh (ph), Bella (ph), Herschel (ph), Toby (ph), Evan (ph) and Linda (ph). Thank you for your work in raising us humans. You truly have made HIDDEN BRAIN possible. I'm Shankar Vedantam, and this is...UNIDENTIFIED INFANT: (Babbling).VEDANTAM: (Laughter) This is NPR.UNIDENTIFIED INFANT: (Babbling) Muh - Mom. Transcript provided by NPR, Copyright NPR.