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CHAPTER 6 CHILD LANGUAGE ACQUISITION
KENDALL A. KING
CHAPTER PREVIEW
How children acquire language has long intrigued scholars and nonscholars alike. Parents of young children are often amazed at how quickly their babies move from cooing and babbling to forceful one- and two-word demands. Linguists and psychologists, in turn, have been interested in understanding the stages and mechanisms by which all children become competent users of language (or, in most of the world, languages) by age three or four. Indeed, children from all backgrounds, and under diverse learning conditions, tend to pass through similar phases in learning their mother tongues. Researchers are interested in exploring this process to gain a better understanding of how children accomplish this remarkable feat, but also because the nature of these process-es holds important implications for larger debates in the field of linguistics. Understanding the mechanisms of how children acquire their language(s) can shed important light on the nature of language, as well as on the nature of human learning.
This chapter will first explore how researchers gather data on child language acquisition. We will review three approaches to child language acquisition research: parental diaries, observational studies, and experimental studies. After briefly discussing the advantages and disadvantages of these research approaches, we’ll turn to the actual data. Specifically, we will look at the major milestones of language development in phonology, semantics, morphology, and syntax. We’ll also examine the extent to which these processes differ depending on the cultural context and the language being acquired. Lastly, after reviewing some of the major research findings, we will consider how researchers explain these data, outlining the major theoretical positions in the hotly debated field of child language acquisition.
GOALS
The goals of this chapter are to:
- introduce the main research methods for investigating child language acquisition
- describe the milestones of child language development
- provide an overview of crosslinguistic and crosscultural aspects of child language acquisition
- analyze the major theories employed to explain child language acquisition
Gathering data on language acquisition
How can we best study how children learn to use language? Because our research subjects are so young, traditional means of data collection are often inadequate. We cannot, for instance, ask a one- year-old to judge the grammaticality of a sentence. Children’s language comprehension skills generally outpace their production abilities, so relying on children’s ver-bal output alone provides only a partial picture of the acquisition process. Furthermore, recent research suggests that language learning begins even before birth: for instance, infants show a preference for the sounds of their mother’s native language just days after being born, thus indicating that some kind of language learning has taken place in utero, long before sub-jects can serve as research participants in most studies.
In collecting and analyzing child language, researchers often strive for naturalness and representativeness in their data. Natural data are simi-lar to the language children use in everyday life with familiar conversa-tional partners (like the child’s parents) in familiar contexts (like the home) doing routine activities (like playing). Representativeness refers to two goals: first, the language data collected from a particular child should be representative of the language used by that child every day. Thus, if a bilingual child normally speaks mostly Spanish with his/her mother, a sample of English conversation between the mother and child would not be representative of their everyday interactional patterns. Second, the children studied should be representative of the general population under investigation – for example, Spanish–English bilingual four-year- olds. Below, three approaches to collecting child language data are briefly described and critiqued in terms of naturalness and representativeness.
Parental diaries
Some of the earliest studies of child language acquisition are found in par-ents’ detailed descriptions of their children’s language development, gen-erally referred to as parental diaries. While early attempts date as far back as the eighteenth century, most parental diaries, such as those of Charles Darwin, come from the late nineteenth and first half of the twentieth century. The most famous of these is Werner Leopold’s four-volume account of his daughter Hildegarde’s simultaneous acquisition of German and English. Leopold was a German–English bilingual of German ances-try; his wife was an American with German roots, but English was her dominant language. Leopold kept meticulous notes beginning at Hildegarde’s eighth week of life, with most of the data focusing on her first two years. He also theorized extensively in his diaries and described his working hypotheses on her language development.
Leopold’s diaries provide rich details and important insights into the process of language learning in general as well as bilingual language acquisition in particular; however, they suffer from many of the short-comings of all parental diary studies. An inherent problem in this type of research is the fact that a diary consists of one observer who is taking notes on just one child, raising the question of whether Hildegarde is represen-tative of all children. Furthermore, the only linguistic forms described in great detail are the utterances that Hildegarde directed at Leopold or which she used around Leopold, providing a potentially limited and unrepresentative sample. There are probably errors and omissions in tran-scription, compounded by the fact that there were no audiotapes of the
language behavior and how linguistic competence develops, with an emphasis on how these patterns of interaction and parents’ ideologies about language vary crossculturally. For instance, in some families, chil-dren are viewed as conversational partners from birth, with cries, grunts, and early babbling sounds treated as meaningful communication attempts (see Figure 6.1). This is far from universal, however; in much of the world, infants’ early sounds are not assigned any particular meaning or communicative intent.
Observational studies have tended to be longitudinal – that is, they have followed the same participants over several months or perhaps as long as several years. Cross-sectional observational studies, although less common, have also been conducted. These studies record the language behavior of participants from at least two different groups; for instance, a group of two-year-old Korean-American children and a similar group of two-year-old Mexican-American children might be compared in a cross-sectional study.
Because of the time-intensive nature of collecting, transcribing, and analyzing hours of language data in such close detail, often these obser-vational studies include only small numbers of child participants. Thus, while observational studies such as these get high marks for providing rel-atively natural data as well as data which are representative of the child’s normal speech, it is not always clear to what extent the few participants are representative of the wider population under study. One way researchers have attempted to overcome this drawback has been to share their transcripts. The primary channel for doing so is the Child Language Data Exchange System (CHILDES; see http://childes.psy.cmu.edu/). CHILDES has allowed researchers not only to examine acquisition patterns and processes across larger numbers of children, but also to investigate how patterns differ across children from different language groups.
Experimental studies
Experimental studies constitute a third approach to collecting child lan-guage data. A wide range of methodological approaches falls under this rubric, including those which are more naturalistic in design and those which involve more tightly controlled tests. In general, experimental studies tend to have narrowly defined research questions (for example, at what age can infants recognize their own name or the sound of their mother’s voice?) and to use more controlled (and sometimes considered artificial) methods of collecting data, such as the HASP described below. Experimental language data tend to be elicited through carefully designed techniques rather than observed and described as they naturally unfold. Lastly, experimental studies tend to collect less data overall from each participant, but to have a greater number of participants. This means that although the data might be less naturalistic, they have a higher chance of accurately representing the population under study.
One of the most widely used experimental procedures to investigate when and how infants begin to make sense of the language around them is the high amplitude sucking paradigm (HASP). This procedure relies on infants’ reactions to stimuli – in particular, the fact that they will suck at a higher rate when presented with novel stimuli. Using a pacifier attached to a machine which records the rate and strength of the infant’s sucking, researchers can measure, for instance, whether the infant perceives a dif- ference between two similar sounds or two words, such as lice and rice. In order to
test this, the infant is given a pacifier and then presented with, for instance, the word lice. At first, the rate of sucking increases, but as lice is presented repeatedly, the infant becomes “bored” with the sound and the rate begins to decline. At this point, rice is presented; if the rate of sucking increases again, researchers interpret this as evidence that the child has detected the new sound and thus can discriminate between lice and rice. If the rate of sucking remains the same, one can assume the child does not distinguish between the two stimuli. This technique can be used with infants who are only a few days old, as all babies are born with a sucking reflex.
In addition to techniques aimed at measuring auditory discrimination, there are also a number of methods for assessing the production and com- prehension of children’s syntax. For example, in elicited production, a game (for example, with a puppet) or a picture is used to lead children to produce particular sentences. (The “wug” test discussed below is an exam-ple of elicited production.) Another commonly used technique is the truth-value judgment task. Here, the child is presented with a story (typi-cally acted out with puppets or shown with pictures) and then asked to render a yes/no judgment about whether a statement accurately describes what happened in the story. Such techniques have been important in revealing much of what we know about children’s early language abilities, the topic of the following section.
The data: milestones in child language development
All normally developing children, acquiring any of the world’s spoken or signed languages, follow a similar path of language development and reach the major milestones in the same order. However, there is signifi-cant variability in the age at which these milestones are reached.
The first sounds
The techniques described above have yielded much of what we know about infant language ability in the early months, and in particular what we know about the development of speech perception during the first year of life. Speech perception – which includes, for instance, the ability to seg-ment the speech stream into meaningful units, to recognize one’s own name in the speech stream, or to distinguish between similar sounding vowels (e.g. /ee/ and /oo/) – is a critical skill that infants develop early in life. These early language skills also involve visual information; for instance, infants as young as two months have been shown to be able to match vowel sounds they hear with the appropriate lip, mouth, and face movements. These early speech perception skills related to the sound structure of lan-guage may help infants to bootstrap into more complex language compe- tencies; bootstrapping refers to the possibility that skills in one area of lan-guage might help the child to develop competencies in other language areas. For instance, infants’ ability to recognize their own names in the speech stream (which appears around the fifth month) may provide them with a means to recognize novel, adjacent words. (See Box 6.1.)
Box 6.1 How familiar names help babies begin to segment speech
How do infants learn to segment the speech stream and to recognize individual words? Bortfeld et al. (2005) provided evidence that infants can exploit familiar words, such as their own names, to segment adja-cent unfamiliar words from a fluent stream of speech. In other words, infants’ names appear to serve as an “anchor” in the speech stream, helping them to disambiguate the words which come just after theirname.
or [ñ]. Labial sounds such as [b] and [m] are also common. Babbling begins to conform to the sound patterns of the adults’ language between six and ten months of age, with adult native speakers showing the ability to discriminate the babbles of Chinese, Arabic, English, or French infants.
Babbling is seemingly innate and unconscious, but also interactive and social. All infants, including those who are born deaf, go through a peri- od of oral babbling. Deaf infants’ oral babbling tends to consist of a small- er total number of sounds, with certain consonants (e.g. nasals and frica-tives) predominating. Their babbling is random, generally not interactive, and tapers off sooner than that of hearing infants. However, deaf infants who are learning a signed language, such as American Sign Language (ASL), also go through a period of “gestural babbling,” which corresponds to signed language and greatly differs from the much more random ges-turing of hearing babies without this exposure.
Although there is no meaning (such as a demand for food) associated with this babbling for hearing or for deaf infants, it can be a source of inter- active play. In some cultures, infants are encouraged to continue to babble by caregivers’ smiles or touches, or by their own babbling in return. Infants will often stop babbling in order to listen to their interlocutor (sometimes engaging in give-and-take exchanges known as proto-conversations), and around the fifth month, some infants are able to immediately imitate simple sound sequences presented to them.
The first words
Sometime around their first birthdays, children begin to assign specific meanings to the sounds they produce. These first words mark the begin-ning of what is known as the holophrastic stage. Holophrastic means ‘characterized by one-word sentences’; infants tend to use single words to communicate a variety of complex functions. For instance, the word mama might be a bid for mother’s attention, a descriptive comment upon seeing mother walk past, or a request for something which mother typically pro- vides, such as food. Through contextual cues, parents often claim to understand the meaning of these holophrases (engaging in what is some-times called “rich interpretation”), although this is difficult to verify empirically. While parents are often very proud of a child who is an early talker, there is little evidence that the timing of the first words corre-sponds to later intelligence or age of achievement of other developmental milestones. (Indeed, Albert Einstein reportedly did not start talking until age three or four!)
Children’s words at this stage tend to be concrete objects which are grounded in and central to everyday experiences and interactions (such as light, tree, water), rather than abstract concepts (peace, happiness). These first words tend to be content words (bear or bed) rather than function words (the, and, on). For children learning English, most first words are nouns. This seems to be related to the fact that sentences in English typically end with nouns, where they are salient, or more noticeable, to learners. This is not the case for children learning all languages, however. For instance, Korean-learning infants’ first words are often verbs; in the Korean lan-guage, verbs are sentence-final and sentences may consist of only a verb.
While working to master the vocabulary around them, children often engage in both semantic overextension and underextension. For instance, a child may overextend the meaning of the word
water to include not just drinking water, but also juice, milk, and soda. Underextension, which seems to be less common, refers to the reverse phenomenon: a child, for example, might use baby only to refer to an infant sibling and not to the other babies he/she encounters.
Around age two, children enter the two-word stage, characterized by use of phrases which are not more than two words. For English-learning infants, this typically means combining a subject and verb (e.g. baby cry, mama sleep) or a verb and modifier (e.g. eat now, go out). The ordering of these two- word phrases is not fixed, however, and there tends to be limited systematic use of grammatical morphology (for example, the possessive is formed as Miranda bed rather than Miranda’s bed).
As in many other stages of their linguistic development, children’s capacity for comprehending words outpaces their production ability. For instance, around the age of one, children can typically understand about seventy different words, but only productively use about six. There is about a four- to six-month delay between when children can comprehend a given number of words and when they can produce that many words them-selves. Sometime around the end of the second year, children’s productive vocabulary begins to develop rapidly; this is sometimes known as the vocabulary spurt. During this period, children begin to add about two hundred words a month to their vocabularies! At approximately two and half years of age, children begin to produce phrases of three or more words, entering the multi-word stage (e.g. Graham go out, Daddy cook dinner, Baby food all gone). Children’s language at this stage has been described as telegraphic speech because, like the eco- nomical language used in telegraphs, it is seemingly direct and makes only limited use of morphological and syntactic markers.
First sentences: morphological and syntactic development
Many diary, observational, and experimental studies have documented and explored how children become competent users of their language’s system of morphology and syntax. From this research, we know that for all languages, both signed and spoken, this process seems to involve the formation of internal “rules”; in other words, children’s increasingly regular use of grammatical forms (even non-adult-like or “incorrect” usages such as broked or foots) may reflect children’s developing grammat-ical rule systems.
We also know that children seem to begin to acquire this grammatical competence at a very young age and, as in vocabulary development, com-prehension skills outpace production. For instance, children who are only seventeen months of age, and typically still producing only one- or two- word utterances, tend to look longer at video clips that correctly corre- spond to the grammar of the oral commentary. For instance, children who hear “The bear sat on the bird” and are shown two pictures (one of a bear sitting on a bird and another of a bird sitting on a bear) will look longer at the picture where the bear is sitting on the bird. This research demon- strates that even at very young ages children are tuned into the semantic significance of their language’s grammatical structures.
Research has also demonstrated that morphological and syntactic devel-opment is predictable. In other words, all children follow similar patterns and pass through the same developmental sequences as their competence develops. Although there is some variation depending on the language being acquired, many patterns and processes are constant across different language and
