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Why your baby prefers infant-directed speech

Babies learn to communicate through eye contact, gestures, and affectionate touch. But when it comes to grabbing a baby’s attention — and helping a baby “crack the code” of spoken language — one particular mode of communication may be especially effective. How do babies learn language? You might argue that they simply have a knack for it. After all, babies perform some truly amazing feats. They listen to a sea of confused sound, and figure out that certain segments of sound are words. They teach themselves to reproduce the speech sounds they hear — by listening, babbling, making corrections, and babbling again. They infer the meanings of words by interacting with conversation partners and observing contingencies (noticing, for example, that you consistently say the word “water” when you give your baby a sippy cup of H2O). However you look at it, it’s impressive. Without textbooks or dictionaries or explicit instruction, babies acquire language. But that doesn’t mean that babies work everything out on their own, without any help. If you’ve ever struggled to understand a new language, you know that not every speaker is equally easy to understand. Some folks, noticing your difficulties, alter their normal speech patterns to make their meanings more obvious. Does the same thing happen for infants? Enter Exhibit A: “infant-directed speech.” What is infant-directed speech? Also called “IDS,” “parentese,” or “motherese,” it’s a speech register that people seem to adopt naturally when they interact with a baby. Suddenly their vocal pitch goes up. They speak more musically — using a wider pitch range, and a more exaggerated emotional tone. They may change the timbre of their voices, too, so they sound smoother, less rough. In addition, they may repeat phrases, speak more slowly, and take extra care in pronunciation — hyper-articulating their vowels. They may also use shorter, simpler sentence structure, and emphasize certain words by uttering them in isolation. For example, instead of saying “Look at the teddy bear!” a parent might simply call out “Bear!” (Christia and Siedl 2013; Fernald 2000). Do babies like infant-directed speech? They do. In fact, when researchers have done experiments using audio playbacks, they’ve found that babies actually prefer IDS to regular, “adult-directed speech” (or “ADS”). The effect has been documented in a wide range of age groups — from newborns all the way up children 18-21 months old (Cooper and Aslin 1990; Hayashi et al 2001; Schachner and Hannon 2011; Byers-Heinlein et al 2021). In fact, babies prefer infant-directed speech even in cases when the language itself is totally unfamiliar — a foreign language they have never heard before (Werker et al 1994). And the thing is, this isn’t simply a question of putting a smile on your baby’s face. Experimental research also indicates suggests that babies’ brains pay more attention to infant-directed speech — processing it, or tracking it, more intensively than they do with adult-directed speech (Saito et al 2006; Zaigl and Mills 2007; Räsänen et al 2018; Kalashnikova et al 2018; Menn et al 2022). Why is infant-directed speech so good at grabbing a baby’s attention? In part, it’s because of the raised pitch. High-pitched vocalizations are used as attention-getters by many nonhuman animals, including monkeys (Koda and Masataka 2003). And it’s interesting to note that baby dogs really love it when we address them with high-pitched voices (Ben-Aderet et al 2017)! So maybe our infants are simply following that trend! In addition, clever experients have confirmed that babies prefer infantile voices — voices that sound a lot like them (Massapollo et al 2016; Polka et al 2022). Is this because such voices sound less threatening (Kalashnikova et al 2017)? Maybe. But it’s probably also about learning to talk. Babies need to tune into their own voices, so they can practice making speech sounds, listen to their progress, and make the necessary tweaks to improve accuracy. So being more attracted to baby voices makes sense. It helps ensure that they will pay close attention to their own, developing, vocal skills. Finally, it’s likely that babies are attracted to the musical, emotional tone of IDS. Given the choice, babies prefer listening to voices infused with emotion — especially happy emotion (Kao et al 2022). And a recent study suggests that it’s the musical rhythms of IDS that encourage the brain to engage in deeper processing (Menn 2022). So how does infant-directed speech help babies understand our meanings? We’ve already seen part of the answer: You are more likely to engage your baby’s attention when you use infant-directed speech. That’s a crucial prerequisite for all communication. But there’s more. 1. Infant-directed speech makes emotional intentions more obvious Babies are in the process of learning language, so they don’t understand many of our words. But infant-directed speech comes with a kind of metaphorical megaphone — we tend to pump up the intensity of our emotional communication. And this helps get our message across. For example, suppose I asked you to listen to a stranger speaking a language you don’t understand. Would you be able to make out his intentions, based on tone of voice alone? When researchers have performed tests like this, they’ve found that the speaker’s style matters. Infant-directed speech makes the emotional intentions more transparent and easier to grasp — for both babies (Fernald 1993) and adults (Bryant and Barret 2007; Bryant et al 2012). 2. Infant-directed speech helps babies decode spoken language Experiments suggest that IDS can help babies develop crucial speech perception skills, including the ability to discriminate between different speech sounds; the ability to detect the boundaries between words in a stream of speech; the ability to recognize distinct clauses in a stream of speech; and the ability to “read lips,” or match visual cues to their corresponding speech sounds. Does this imply that infant-directed speech is a kind of “tutorial” mode of baby communication? It seems to. In fact, there is even evidence suggesting that babies learn speech faster when their parents use particularly expressive forms of infant-directed speech. For instance, in families where parents use infant-directed speech, babies who spend more time in one-on-one conversation develop better language skills (Ramírez-Esparza et al 2017). Moreover, toddlers tend to amass larger vocabularies — and learn new words more easily — if their mothers address them with a higher pitch (Han et al 2023; Han et al 2022). Who uses infant-directed speech? Does everybody do it? Well, no. Some adults don’t make any of the modifications we’ve mentioned. But it’s very common for people to adopt at least one of the characteristics of infant-directed speech, and in that sense, it’s the “normal” thing to do. For example, in a recent international study, researchers asked volunteers from over 180 different countries to listen to a series of audio clips — brief monologues of unidentified adults speaking briefly in their native languages. In some cases, the speakers had been addressing another adult. In others, they had been talking to a “fussy infant.” Could the volunteers tell which was which? People were quite accurate, even when they didn’t understand the speaker’s native language. When they heard speakers raising their pitch — or hyper-articulating their vowels — they tended to assume that they were listening to infant-directed speech (Hilton et al 2022). Is infant-directed speech a human universal? Not in the literal sense. As we’ve alread noted, infant-directed speech isn’t practiced absolutely everywhere by everyone. Parents who are depressed or self-conscious aren’t so good at ID speech (e.g., Kaplan et al 2007). And some parents may be discouraged by cultural attitudes. For instance, anthropologists have reported that the Kaluli of New Guinea don’t engage their babies in conversation (Sheiffelin and Ochs 1996). It’s also been reported that the Quiché Mayan speak to their babies in the same pitch that they use to address adults (Ratner and Pye 1984). Yet it’s clear that infant-directed speech is a widespread, cross-cultural phenomenon (Das 1989; Dil 1971, Ferguson 1964; Fernald et al 1989; Fernald and O’Neill 1993; Kelkar 1965; Meegaskumbura 1980; Saint-Georges et al 2013; Sulpizio et al 2017). It’s been documented in a wide range of languages, including languages indigenous to Africa and the Middle East (Arabic and Xhosa, a Bantu language)