Children Language Learning

WHAT IS LANGUAGE ACQUISITION?
Language acquisition is a journey that begins in the fluid world of the womb and continues throughout childhood, adolescence, and even beyond. During this long period of acquisition, the learner faces a vast array of challenges. From the young infant's clumsy attempts to get the articulatory system in his mouth, throat, and larynx to produce the specific sounds of his native tongue, through to the much later complexities of producing and understanding long narratives, the child's language capacities undergo numerous changes. Innovative research techniques now allow us to follow this amazing journey closer than ever before.
In the past, the acquisition literature situated the onset of language at about twelve months, when children produce their first recognizable words. We have now come to realize that acquisition gets under way long before this, even prior to birth. From as early as twenty weeks gestation, the hearing system of the fetus is sufficiently developed to enable it to begin processing some of the sounds that filter through the amniotic liquid. The fetus's world is filled with a cacophony of gurgles and grumbles from the mother's body, along with the constant rhythm of her heartbeats. These noises provide early auditory stimulation. But most stimulating of all are the filtered sounds of language.
From the sixth month of gestation onward, the fetus spends most of its waking time processing these very special linguistic sounds, growing familiar with the unique qualities of its mother's voice and of the language or languages that she speaks. It also becomes sensitive to the prosody—the intonation of sentences and rhythm patterns within words—that structures her speech. In its last three months in the womb, the fetus is busy eavesdropping on its mother's conversations—an important preparation for life in the outside world. Already equipped with some experience of what language sounds like, the newborn comes into the world prepared to pay special attention to human speech, and specifically to his mother's voice. These earliest intrauterine experiences prime the newborn for linguistic input and can therefore be viewed as playing an important role in the overall process of language development.
Just as the fetus is capable of listening in on its mother's conversations, so have new research methods allowed scientists to eavesdrop on the sounds that fill its intrauterine world. Minute microphones, placed outside the wall of the uterus, can measure the noises that filter through to the womb, and ultrasound techniques record fetal responses to what it is hearing. We can now determine not only what the fetus hears, but also whether it distinguishes between different sounds. Experiments carried out only moments after birth then provide us with vital clues about the effects of the prenatal auditory experiences on newborn behavior. With such data, scientists are now able to raise questions about the extent to which the neonate remembers what he heard in utero. Can he recognize his mother's voice even though it is no longer filtered through liquid? Can he distinguish between his mother tongue and other hitherto unheard human languages? And what has he learned about the sound structure of speech?
These are truly fascinating times for students of developmental psycholinguistics. Until recently, acquisition research focused almost exclusively on language production. Nonverbal communicative behavior and vocalizations before the age of twelve to fifteen months were considered to add little to our knowledge of language acquisition—the focus was on production of recognizable words. Now, by contrast, the vital role of early babbling in tuning the articulatory system to the particularities of the infant's native tongue is the subject of numerous in-depth studies. Over the last two decades, novel infancy research techniques have been developed that shed light on these much earlier stages of language learning. Along with a new understanding of fetal and neonatal speech processing, the importance of early mother-infant nonlinguistic dialogue has been recognized. The amount and nature of early adult-infant interaction may of course vary from culture to culture, and such differences help researchers decide which aspects of the social environment are crucial to language acquisition.
We now have at our disposal a whole range of innovative methods for discovering what infants understand prior to their own first words. There is therefore no longer a need to rely solely on what children say in order to gauge their level of linguistic knowledge. Researchers can now explore, better than ever before, how speech perception and language comprehension develop during the crucial period preceding the first production of recognizable words. Modern research techniques have allowed us to discover hitherto unsuspected infant capacities for speech segmentation. They have also pointed to the much earlier emergence of the infant's realization that words refer to objects, people, places, and actions. We now know that well before two years, infants already understand that word order, for instance, conveys crucial information about meaning. Scientifically controlled experiments with prelinguistic infants are now commonly used to further our knowledge of the roots of language acquisition.
Although by the age of five most children speak fluently and with ease, language acquisition is far from complete. Children continue to acquire complex grammar and new linguistic meanings during their school years. Other aspects of language learning persist into adolescence and even through adult life. And because language is dynamic, even as adults we have to continually adapt to changes that occur in our native tongue throughout our lives. The constant updating of dictionaries is clear evidence of the changing nature of language, with new entries of modern terms like "e-mail," "modem," and "internee posing a threat to words like "typewriter" that may one day become obsolete.
The field of psycholinguistics was created as a meeting ground for psychology and linguistics (which analyzes the structure of language). Developmental psycholinguistics, in particular, addresses how these two aspects of language are progressively acquired by children. A detailed account of all the different psychological and linguistic approaches in the field is beyond the scope of this book. So we will refer to the theories that pertain specifically to the issues concerning how language is acquired—our central focus here. At the heart of this debate is the issue of innateness. Does the newborn come into the world prewired for language acquisition as a result of our human evolutionary history? Are there specialized mechanisms in the brain just for language learning? Or does the infant learn language in much the same way as he learns about the physical and social worlds? Opinions are deeply divided. Arguments revolve around the dichotomy between nature and nurture . No theory denies that both nature and nurture play some role in language learning. Rather, theories differ fundamentally as to the importance of each. It is true that we are the only species to develop full-fledged grammatical languages. Something, therefore, must be specific to human biology to have enabled us to do this. But nurture must also play an important role. There are some six thousand different languages in the world, and it is obvious that no child is born already knowing English, Swahili, or Russian. Experiencing input as part of everyday life from a particular language (or more than one language) is thus essential for acquiring native tongues. The argument among theorists of language acquisition ultimately revolves around whether nature or nurture plays the leading role.
Nativist theories of language acquisition, which argue for the existence in the infant brain of innate or prewired linguistic structure, have been particularly influential since the 1960s. This is when the famous American linguist Noam Chomsky demonstrated that behaviorism (which holds that the newborn brain is a tabula rasa, or blank slate on which experience simply imprints its structure) could not alone account for language acquisition. Chomsky argued that for complex grammar to be acquired, input simply does not provide sufficient examples to allow the child's brain to build grammatical structures from scratch and to know, for instance, which words are nouns or verbs and which parts of sentences can and cannot be moved. If the child based his hypotheses about linguistic structure simply on what he heard, he would draw a large number of erroneous conclusions about the grammatical structure of his native tongue. Hence behaviorism cannot account for language acquisition.
There are several versions of the nativist approach, but the central tenet is that infants are born with a so-called Universal Grammar (or UG) and specialized language-learning mechanisms for acquiring their native tongue. From this viewpoint, a common set of universal principles underlie every one of the world's languages, despite the very different surface characteristics of each language. Nativist theorists tend to argue that children are born prewired with these linguistic principles and set of parameters, which are simply triggered by the specific linguistic input. The nativist view claims that linguistic experience is needed only to allow the child to discover the local realization of universally specified principles and parameters. The brain mechanisms by which the child learns language are considered to be not only innate, but also entirely domain specific—that is, dedicated only to language learning.
At the opposite theoretical extreme is the cognitive view of language learning propounded, in particular, by the famous Swiss psychologist Jean Piaget. For Piaget and his followers, language acquisition calls on the same general learning mechanisms that the child uses to learn about physics, number concepts, space, social conventions, and so forth. According to this approach, there is nothing unique about the way in which children learn language. Cognitive development is deemed to be a prerequisite and foundation for language learning. Thus for Piaget, concepts like "object permanence" are seen to underlie the onset of early word use. One of Piaget's disciples, Hermine Sinclair, also argued that the child's ability to nest a set of Russian dollslays the foundations for the child's subsequent capacity to understand how sentences can be
embedded within one another. The cognitive view, then, claims that general learning mechanisms are simply applied to linguistic input once they have become established in general cognitive development.
Other theorists place social interaction at the center of their claims about the processes of language acquisition. Jerome Bruner, for instance, has stressed the importance of the principles of interaction for language learning. Beginning within the mother-infant relationship, and subsequently expanding to the rest of the child's social environment, conversational conventions help children become sensitive to the rules for dialogue and turn-taking. Such theories may explain how children enter the world of dialogue, but say little about how the intricacies of grammar are acquired. They seem to assume that there is enough information in the day-to-day linguistic input for the child to discover the structure of his native tongue. For both the cognitive and social views, the mechanisms by which the child learns language are therefore domain general: they are the same as those used for learning about other aspects of the world.
The debates that separate these different theoretical positions will arise throughout the book because they influence both the kinds of hypotheses constructed and how the research data are ultimately interpreted. We argue, however, that the nature versus nurture dichotomy is not a useful one, and that we should focus instead on the dynamic interaction between the two. Our view is that language is indeed special, but we hypothesize that evolution's solution has not been to prewire complex linguistic representations into the neonate mind. Rather, we believe that evolution has done two interesting things. First, evolution has made the period of postnatal brain development in humans extremely long, so that environmental input can shape the structure of the developing brain. But the brain is not in our view a blank homogenous slate, as behaviorists would hold. Our second argument is that evolution has provided us with a number of different learning mechanisms that, although not domain specific, are what we would call "domain relevant." It is by interacting with various environmental inputs that each mechanism becomes progressively more domain specific. By this we mean that prior to and at birth, the infant possesses some minimal predispositions that make him pay particular attention to certain parts of the environment like, say, faces and voices. From the start, different brain mechanisms will be more attuned to processing one type of input over another. Thus a mechanism that is sensitive to sequential, fast-fading input might pay particular attention to oral or signed language but not to faces, and as it becomes increasingly specialized at processing language, it will become more devoted to that specific domain. This is why we end up in adulthood with such specialized language areas in the brain. In other words, the infant brain does not start out with circuits dedicated only for processing language, but it does end up with specialized circuits as a function of experience. So, our view considers language knowledge to be the complex product of the interaction between some initial, domain-relevant predispositions and the rich structure of the linguistic input. Thus it is not a question of nature or nurture; rather it is about the intricate interaction between the two. An understanding of this interaction will ultimately explain how the dynamic process of language acquisition takes place from fetus to adolescent.
It may be hard for the reader to imagine how we can carry out language-related experiments on very young infants who cannot yet speak. Yet we will see just how inventive researchers have been in devising carefully controlled methods that shed light on both fetal sensitivity to speech input as well as language processing in the early postnatal months. Other methods can now probe the linguistic knowledge of toddlers and older children in greater depth than ever before. These provide vital insights into how the mental representations of speech built up during the first few months form the foundations of subsequent language development. In particular, we will consider the difference between so-called off-line approaches, which always involve a degree of metalinguistic awareness, and "on-line" techniques that tap into real-time language processing. We will also describe some of the revolutionary noninvasive brain imaging techniques. These reveal minute changes in blood flow and electrical activity in the brains of infants and young children as they actively process linguistic input. Such images show us how the brain becomes progressively specialized and localized for language during postnatal development.
With a clear understanding of the basic experimental paradigms, the reader will then be ready to explore the pathways to language. In Chapter 3, we examine the role of the fetus's intrauterine auditory experiences in preparing the infant to attend to and process speech during the first few months in the outside world. We will particularly stress the difference between speech and language, and warn against automatically generalizing from one to the other, as sometimes happens in the literature. Early speech processing of the sounds of language cannot be equated with knowledge of the meaning and structure of language. Our main focus in Chapter 3 is therefore sensitivity to speech input, as demonstrated by current research into fetal, newborn, and infant behavior. Most studies of language acquisition have concentrated on middle- to lower-middle-class families and on the English language, and these represent the main sources of data on which theories are based. But the total picture of how language is acquired must also include examination of the world's many different languages whose structures differ from English. Sociocultural variables will also affect a child's patterns of linguistic interaction, and these will in turn influence language acquisition. Wherever possible, we will bring the sociocultural dimension and non-English data into our discussions throughout the book.
Atypical language development in children with focal brain damage and genetic disorders, focusing on Specific Language Impairment, Down syndrome, and Williams syn-
drome. Here we challenge the automatic assumption, often made in the literature on atypicality, that the study of abnormality is necessarily a window on normal language acquisition. We will stress that it is wrong to think of the atypical brain as a normal brain with parts intact and parts impaired. Rather, we argue that the brains of children with genetic disorders show an overall pattern of developmental differences from the outset. Finally, Chapter 8 reexamines the crucial nature-nurture debate against the backdrop of the extensive research data presented in the book. We consider the role of evolution in enabling humans to develop language, how human language differs from the communication systems of other species, and what it ultimately means to have language.
All over the world children learn their native tongues effortlessly. If they cannot hear, they readily acquire the intricacies of sign language. Unlike the development of reading skills, learning a spoken or signed language does not require lessons; it simply happens as a function of development and experience. Yet the complex patterns of linguistic output that children ultimately produce are breathtaking. They can talk or sign about the present, the past, and the future. They can refer to imaginary events and to abstract concepts. They can use language to pass on information, or to trick and deceive. They can play with language, making up new words or new meanings for old words. Language is a system that allows for dynamic change and flexibility. It is vital to human life both as a powerful vehicle for social interaction and as an infinitely creative tool for representing real and hypothetical experiences and feelings. The intricate trajectory that children take in learning the manifold aspects of their native tongue is one of the most fascinating areas of human psychology—and is a journey that the reader is now invited to follow.