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Language development occurs in a social context. Most adults naturally speak to young infants in a sing-song way that attracts their attention. Infant-directed speech, or “motherese,” uses repetition, short words and sentences, high and varied pitch, and long pauses (Thiessen, Hill, & Saffran, 2005). Infants prefer listening to infant-directed speech than to typical adult speech, and they prefer adults who use infant-directed speech (Schachner & Hannon, 2011). EEG recordings show that babies demonstrate more neural activity in response to infant-directed speech than adult speech, suggesting that they are better able to attend to it and distinguish the sounds (Peter, Kalashnikova, Santos, & Burnham, 2016). Infant-directed speech exaggerates sounds, helping infants hear and distinguish sounds, and enables them to map sounds to meanings (Estes & Hurley, 2012; Kitamura & Burnham, 2003; Thiessen et al., 2005). In one study, 7- and 8-month-old infants were more likely to learn words presented by infant-directed speech than those presented through adult-directed speech (Singh, Nestor, Parikh, & Yull, 2009).

When babies begin to engage in canonical babbling, a type of babbling with well-formed syllables that sounds remarkably like language, parents, regardless of socioeconomic status, ethnicity, and home environment, tune in and treat the vocalizations in a new way (Oller, Eilers, & Basinger, 2001). Because the utterances sound like words, parents help infants to associate the word-like utterances with objects and events, encouraging vocabulary development.

Parental responsiveness to infants’ vocalizations predicts the size of infants’ vocabularies, the diversity of infants’ communications, and the timing of language milestones (Tamis-LeMonda et al., 2014). One study showed that infants of highly responsive mothers achieved language milestones such as first words, vocabulary spurt, and telegraphic speech at 9 to 13 months of age, which was 4 to 6 months earlier than infants of low-responsive mothers (Tamis-LeMonda, Bornstein, & Baumwell, 2001). Fathers’ responsiveness to their 2- and 3-year-olds predicted toddlers’ cognitive and language abilities (Tamis-LeMonda, Shannon, Cabrera, & Lamb, 2004). Parental responsiveness is also associated with the language skills of adopted children, supporting the contextual influence of parents.

Babies learn language by interacting with more mature, expert speakers who can speak at their developmental level. Parents often adjust their infant-directed speech to match infants’ linguistic needs by, for example, using longer and more complicated words and sentences as infants’ comprehension increases (Englund & Behne, 2006; Sundberg, 1998). Even as infants learn speech, they continue to display preferences for some features of infant-directed speech. A study of 12- and 16-month-old infants indicated that they preferred the high pitch and pitch variability of infant-directed speech but not the shorter utterances or simplified syntax (Segal & Newman, 2015).

The quality of language input from parents and the number of words children hear is related to their vocabulary size at age 2 (Hoff et al., 2002). Children whose mothers address a great deal of speech to them develop vocabulary more rapidly, are faster at processing words they know, and are faster at producing speech than children whose mothers speak to them less often (Hurtado, Marchman, & Fernald, 2008; Weisleder & Fernald, 2013). The number of words and different grammatical structures used in maternal speech, as well as grammatical complexity, predict the size of children’s vocabulary and understanding of grammar (Hadley, Rispoli, Fitzgerald, & Bahnsen, 2011; Huttenlocher, Waterfall, Vasilyeva, Vevea, & Hedges, 2010).

Although parents do not reliably reinforce correct grammar, they tend to communicate in ways that tell young children when they have made errors and show how to correct them (Saxton, 1997). Adults often respond to children’s utterances with expansions, which are enriched versions of the children’s statements. For example, if a child says, “bottle fall,” the parent might respond, “Yes, the bottle fell off the table.” Adults also tend to recast children’s sentences into new grammatical forms. For example, “Kitty go,” might be recast into, “Where is the kitty going?” When children use grammatically correct statements, parents maintain and extend the conversation (Bohannon & Stanowicz, 1988). When adults recast and expand young children’s speech, the children tend to acquire grammatical rules more quickly and score higher on tests of expressive language ability than when parents rely less on these conversational techniques (Abraham, Crais, & Vernon-Feagans, 2013; Bohannon, Padgett, Nelson, & Mark, 1996).

Table 5.4

Therefore, the interactionist perspective on language development points to the dynamic and reciprocal influence of biology and context. Infants are equipped with biological propensities and information processing capacities that permit them to perceive and analyze speech and learn to speak. Infants are motivated to communicate with others, and language is a tool for communication. Interactions with others provide important learning experiences, which help infants expand their language capacities and learn to think in ways similar to members of their culture (Fitneva & Matsui, 2015). The accompanying feature, Cultural Influences on Development, discusses cultural differences in infant-directed speech. Theories of language development are summarized in Table 5.4.