Babbling and Early Words
BABBLING AND EARLY WORDS
A child's entrance into human society begins with the onset of language development. Parents often acknowledge this accomplishment upon hearing their infant's first words. Research on early language has convinced scientists that the emergence of first words is inseparable from important developmental milestones that occur prior to the recording of these words. Pre-speech vocalizations can be examined narrowly within the verbal domain only, or can be explored in a wider scope as related to cognitive and communicative developments that are established during the first year of life. The study of pre-speech vocalizations flourished during the last quarter of the twentieth century. During the late 1970s and early 1980s, most efforts concentrated on describing the sounds infants produce. In the 1990s, study of pre-speech development expanded in several important directions.
The Form of Infants' Pre-Speech Vocalizations
Pre-speech vocalizations are divided into reflexive vocalizations (e.g., cries, coughs, hiccups), which are related to the baby's physical state, and nonreflexive vocalizations (e.g., cooing, playful productions, yelling), which contain phonetic and syllabic features of speech. Both vowels and consonants appear in nonreflexive vocalizations, and the most prevalent syllable structure is a consonant followed by a vowel (CV; e.g., \ba\, \du\, \ke\). The overall composition of pre-speech vocalizations changes dramatically during the first year of life. In the first six months, babies all over the world sound alike. During this period, vowels predominate and are supported by prolonged back consonants (e.g., \k\, \g\). During the next six months, the sound repertoire significantly expands, with a marked shift toward more frontal consonants. John Locke reported in 1993 that, by their first birthday, American English-speaking infants produce stops (\p\, \b\, \t\, \d\, \k\, \g\), nasals (\m\, \n\), and glides (\w\, \j\).
Stages in the Development of Pre-Speech Vocalizations
Developmental stages of pre-speech vocalizations (e.g., as described by Carol Stoel-Gammon in 1998) are not discrete, and vocalizations from previous stages continue to be uttered subsequently. Novel emergent behaviors define the beginning of a new stage. Ages are assigned to each stage as estimates only, because children differ greatly regarding the timing for recording milestones of early language development.
The first stage (from zero to two months), phonation, is characterized mainly by fussing, crying, sneezing, and burping, which bear little resemblance to adult speech. The second stage (at two to three months), cooing, begins when back vowels and nasals appear together with velar consonants (e.g., \gu\, \ku\). Cooing differs in its acoustic characteristics from adult vocalizations and is recorded mainly during interactions with caregivers. In the third stage (at four to six months), vocal play or expansion, syllable-like productions with long vowels appear. Squeals, growls, yells, bilabial or labiodental trills, and friction noises demonstrate infants' playful exploration of their vocal tract capabilities during this stage.
In the extremely important canonical babbling stage (at seven to ten months), two types of productions emerge: reduplicated babbling—identical, repetitive sequences of CV syllables (e.g., \ma\ma\, \da\da\); and variegated babbling—sequences of different consonants and vowels (e.g., CV, V, VC, VCV = \ga\e\im\ada\). Such productions are not true words, as they lack meaning. Canonical babbling is syllabic, containing mainly frontal stops, nasals, and glides coupled with lax vowels (e.g., \a\, \e\, \o\). The emergence of canonical babbling is highly important, holding predictive value for future linguistic developments. Oller and her colleagues in 1999 argued that babies who do not produce canonical babbling on time are at high risk for future speech and language pathology, and should be carefully evaluated by a language clinician.
In the fifth stage (at twelve to thirteen months), jargon or intonated babble, infants produce long strings of syllables having varied stress and intonation patterns. Jargon sounds like whole sentences conveying the contents of statements or questions, and often co-occurs with real words. Yet, it lacks linguistic content or grammatical structure.
Pre-Speech Vocalizations in Different Target Languages
The early interpretation of similarities in the phonetic structure of babbling among infants who acquire different languages (e.g., Japanese, Hebrew) was that pre-speech vocalizations are universal. This observation was explained by the strong constraints of the mouth's anatomical characteristics and by physiological mechanisms controlling movements of the tongue and palate. Cross-linguistic research in the 1990s revealed, however, that clear influences of segmental and suprasegmental patterns (i.e., intonation and stress) of the input are recognizable in pre-speech vocalizations. This is particularly true during the second half of the first year of life. In a longitudinal comparative study by Bénédicte de Boysson-Baradis (1999) of ten-month-old Spanish, English, Japanese, and Swedish infants, the relative distribution of consonants in their canonical babbling resembled the distribution of these segments in their language. As babies grow, the segmental similarity between their babbling and early words increases. Several studies by Peter Jusezyk and colleagues on speech perception indicate that infants' sensitivity to the acoustics and phonetics of languages increases with age, influencing their ability to discriminate the sequences of sounds and syllable structures typical to their own language. Indirect evidence for the role of audition in the development of pre-speech vocalizations derives from studies on deaf children, who show significant delays in the emergence of canonical babbling and also a decreased variety of consonants uttered from age eight months onward.
Mutual Imitation within Mother-Child Interaction
In 1989 Metchthild and Hanus Papoušsek were among the first researchers to point out that more than 50 percent of two- to five-month-olds' noncrying vocalizations are either infant imitations of mothers' previous vocalizations or mothers' imitations of infants' previous vocalizations. They suggested that this mutual vocal matching mechanism relates to the emotional regulation of communication in the beginning of life. Joanna Blake and Bénédicte de Boysson-Bardies found in 1992 that infants tend to vocalize more while manipulating small objects and especially when adults are present. Edy Veneziano in 1988 analyzed vocal turn taking in pairs of nine- to seventeen- month-old babies and their mothers. She reported that, as children advance toward conventional language, mothers' imitations of what babies say becomes selective. Mothers imitate only those infant vocalizations resembling conventional words, thus signaling to the child what constitutes a linguistic symbol with meaning.
Pre-Symbolic Productions in Hearing and in Deaf Infants
Cumulative research on pre-speech vocalizations clearly indicates that babbling is in fact structurally and functionally related to early speech. Locke argued in 1996 that when variegated babbling emerges, a consistent relation is identified between vocalizations and specific communicative functions (i.e., protest, question, and statement). At around age eighteen months, the child's phonological system is clearly shaped by the target language's phonetic characteristics, and at that time conventional words emerge.
Indirect evidence for the developmental significance of babbling was published in a revolutionary 1991 paper by Laura Petitto and Paula Marentette on hand babbling in two deaf infants of signing mothers. The argument was that these two infants (who were recorded at ages ten, twelve, and fourteen months) produced far more manual babbling than three matched hearing infants at similar ages. The deaf infants' hand babbling also revealed phonetic features of American Sign Language, suggesting that babbling reflects infants' innate ability to analyze phonetic and syllabic components of linguistic input.
Pre-Speech Productions and First Words or Signs
Early words are produced by the child in expected contexts, and hence are recognized by familiar listeners as linguistic units conveying meanings. In 1999 Esther Dromi distinguished between comprehensible and meaningful words. Comprehensible words are phonetically consistent forms resembling adult words that caregivers understand, but that do not yet convey referential meanings. Meaningful words are symbolic, arbitrary, and agreed-upon terms of reference. Considerable variation exists in both the age of speech onset and the rate of early lexical development. Large-scale questionnaire data reported in 1994 by Fenson and his colleagues for English-speaking typically developing children, cited the range of vocabulary size for twelve- to thirteen- month-olds at 0 to 67 different words, and for eighteen- to nineteen-month-olds at 13 to 471 different words. In 2000 Maital and her colleagues reported very similar figures for Hebrew.
Early words are constructed from a limited set of consonants, mainly stops, nasals, and glides. Syllable structures in these words are usually CV, CVC, or CVCV. Several researchers found that during the first few months of lexical learning, many new words are composed from segments that the child is already using in babbling. A number of researchers have proposed that patterns of lexical selection and avoidance reflect the child's production capabilities. When productive vocabularies contain more than a hundred different words, the influences of phonology on the lexicon decline. Nevertheless, children who have relatively larger lexicons of single words also show larger inventories of sounds and syllable structures than children with smaller productive lexicons. Precocious word learners have much larger phonetic inventories than typically developing children at age eighteen months. The major semantic achievement in the first few months of vocabulary learning is the ability to use words referentially. Martyn Barrett and Esther Dromi, who independently carried out detailed longitudinal analyses of repeated uses of the same words over time, have argued that some early words show referential use from their outset, while other words are initially produced only in very specific contexts. Throughout the one-word stage, the phonology of words improves, and meanings become symbolic and arbitrary. A word initially produced in just one situation is now uttered in a much wider range of contexts, until it becomes completely context free and referential. As words become conventional tools for expressing meanings, the amount of pre-speech vocalizations declines and gradually disappears.
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