T H EM E S ❖ The Active Child ❖ The Sociocultural Context ❖ Individual Differences ❖ “Woof.” (used at the age of 11 months to refer to neighbor’s dog) “Hot.” (used at the age of 14 months to refer to stove, matches, candles, light reflecting off shiny surfaces, etc.) “Read me.” (used at the age of 21 months to ask mother to read a story) “Why I don’t have a dog?” (27 months of age) “If you give me some candy, I’ll be your best friend. I’ll be your two best friends.” (48 months of age) “Granna, we went to Cagoshin [Chicago].” (65 months of age) “It was, like, ya’ know, totally awesome, dude.” (192 months of age) T hese utterances, which we will return to throughout the chapter, were all produced by one boy in the process of becoming a native speaker of the English language (Clore, 1981). In beginning to learn his native language, this boy displayed the capacity that most sets humans apart from other species: the creative and flexible use of symbols, including language and many kinds of nonlinguistic symbols (print, numbers, pictures, models, maps, etc.). We use symbols to (1) represent our thoughts, feelings, and knowledge, and (2) communicate them to other people. Our ability to use symbols vastly expands our cognitive and communicative power. It frees us from the present, enabling us to learn from the generations of people who preceded us and to contemplate the future. Because symbols are such an important source of learning and knowledge, becoming symbol-minded is a crucial developmental task for all children everywhere in the world (DeLoache, 2005). In this chapter, we will focus first and primarily on the acquisition of language, the preeminent symbol system—the “jewel in the crown of cognition” (Pinker, 1990). We will then discuss children’s mastery and creation of nonlinguistic symbols, such as pictures and models. The dominant theme in this chapter will once again be nature and nurture. Considerable debate has focused on the relative contributions of nature and nurture in children’s language development. A related disagreement concerns the extent to which language acquisition is made possible by abilities that are specialized for learning language versus general-purpose cognitive mechanisms that support all sorts of learning. These children are intent on mastering one of the many important symbol systems in the modern world. 216 MYRLEEN FERGUSON CATE / PHOTOEDIT Nature and Nurture 217 LANGUAGE DEVELOPMENT The sociocultural context is another theme that is prominent in this chapter. We will frequently discuss research conducted with children from different language communities, citing both similarities and differences in language acquisition across cultures. This comparative work often provides crucial evidence for or against theoretical claims about language development. A third theme that recurs throughout the chapter is individual differences. As you will see, there is great variability in the timing of most aspects of language development. For any given milestone, some children will achieve it much earlier, and some much later, than others. The active child theme also puts in repeated appearances here. Infants and young children pay close attention to language and a wide variety of symbolic artifacts, and they work hard at figuring out how to use them to communicate with other people. Language Development What is the average 5- to 10-year-old almost as good at doing as you are? Not much, but one very important thing is using language. By 5 years of age, children have mastered the basic structure of their native language, whether spoken or manually signed. The sentences uttered by the average 1st-grade student are just as correct grammatically as those produced by the average college freshman. Although their powers of expression may be less sophisticated than yours and their vocabularies smaller, 1st graders’ basic linguistic competence is not. Using language involves both language comprehension, which refers to understanding what others say (or sign or write), and language production, which refers to actually speaking (or signing or writing) to others. As you will see repeatedly in this chapter, language comprehension precedes language production: children understand words and linguistic structures that other people use before they include them in their own utterances (Goldin-Meadow, Seligman, & Gelman, 1976). This is, of course, not unique to young children; you no doubt understand many words that you never actually use. In our discussion, we will be concerned with developmental processes involved in both comprehension and production, as well as the relation between them. The Components of Language Each of the thousands of languages in the world is based on a complex system of rules for combining different kinds of elements at different levels of a hierarchy: sounds are combined to form words, words are combined to form sentences, and sentences are combined to form narratives. Thus, acquiring a language involves learning its sounds and sound patterns, its specific words, and the ways in which the language allows words to be combined. It also involves learning how language is employed for communication with other people. The enormous benefit that emerges from this combinatorial process is generativity; using the finite set of words in our vocabulary, we can generate an infinite number of sentences, expressing an infinite number of ideas. The generative power of language comes at a cost, however, and the cost is complexity. To appreciate the challenge that this complexity presents to children who must master their native language, imagine yourself as a stranger in a strange land. Someone walks up to you and says, “Jusczyk daxly blickets Nthlakapmx.” You would have absolutely no idea what this person had just said. Why? ❚ symbols ❚ systems for representing our thoughts, feelings, and knowledge and for communicating them to other people ❚ language comprehension ❚ understanding what others say (or sign or write) ❚ language production ❚ speaking (or writing or signing) to others ❚ generativity ❚ refers to the idea that through the use of the finite set of words in our vocabulary, we can put together an infinite number of sentences and express an infinite number of ideas 218 ❚ phonemes ❚ the elementary units of meaningful sound used to produce languages ❚ phonological development ❚ the acquisition of knowledge about the sound system of a language ❚ morphemes ❚ the smallest units of mean- ing in a language, composed of one or more phonemes ❚ semantic development ❚ the learning of the system for expressing meaning in a language, including word learning ❚ syntax ❚ rules in a language that specify how words from different categories (nouns, verbs, adjectives, etc.) can be combined ❚ syntactic development ❚ the learning of the syntax of a language ❚ pragmatic development ❚ the acquisition GETTY IMAGES / DIGITAL VISION of knowledge about how language is used In this everyday conversation, these young boys are generating totally novel sentences that are correct in terms of the phonology, semantics, and syntax of their native language. They are also making appropriate pragmatic inferences regarding the content of their partner’s utterances. CHAPTER 6 DEVELOPMENT OF LANGUAGE AND SYMBOL USE First, you may have difficulty even perceiving some of the sounds that the speaker is uttering. Phonemes are the elementary units of sound used to produce languages, and they distinguish meaning. For example, “rake” differs by only one phoneme from “lake” (/r/ versus /l/), but the two words have quite different meanings to English speakers. Languages employ different sets of phonemes; English, for example, uses 45 of the roughly 200 sounds used in the world’s languages. The phonemes that distinguish meaning in any one language overlap with, but also differ from, those in other languages. For example, the sounds /r/ and /l/ do not carry different meaning in Japanese. Further, combinations of sounds that are common in one language may never occur in others. When you read the stranger’s utterance in the preceding paragraph, you probably had no idea how to pronounce “Nthlakapmx,” because the sound combinations that the letters of this word represent do not occur in English. Thus, the first step in children’s language learning is phonological development, the mastery of the sound system of their language. Another reason you would not know what the stranger had said to you, even if you could have perceived the sounds being uttered, is that you would have had no idea what the sounds mean. The smallest units of meaning are morphemes, which are composed of one or more phonemes. Morphemes, alone or in combination, constitute words. The words I and dog, for example, are both single morphemes, because each of them refers to a single entity. The word dogs contains two morphemes, one designating a familiar furry entity and the second indicating more than one of them. Thus, the second component in language acquisition is semantic development, that is, learning the system for expressing meaning in a language, including word learning. However, even if you were told the meaning of each individual word the stranger had used, you would still not understand the utterance because, in all languages, meaning depends on how words are put together. To express an idea of any complexity, we combine words into sentences, but only some combinations are permissible. For every language, a large set of rules—the syntax of the language— specifies how words from different categories (nouns, verbs, adjectives, etc.) can be combined. In English, many grammatical rules pertain to the order in which words can appear in a sentence, because word order affects meaning. “John loves Mary” does not mean the same thing as “Mary loves John.” In some other languages, which person is the lover and which the beloved would be conveyed by word endings or subtle differences in sound rather than by word order. The third component in language learning, then, is syntactic development, that is, acquiring the rules for combining words in a given language. Finally, a full understanding of the interaction with the stranger would necessitate some knowledge of the cultural rules for using language. In some societies, it would be quite bizarre to be addressed by a stranger in the first place, whereas in others it’s commonplace. Pragmatic development refers to acquiring knowledge about how language is used. Our example of the bewilderment one experiences when listening to someone speak a language one does not know is useful for delineating the components of LANGUAGE DEVELOPMENT 219 language use. However, as an analogy to what infants and young children face in learning language, it is limited. An adult who hears someone speaking an unfamiliar language already knows what language is, knows that the sounds the person is uttering constitute words, knows that words are combined to form sentences, knows that only certain combinations are acceptable, and so on. In other words, in contrast to young language learners, adults have considerable metalinguistic knowledge—that is, knowledge about language, including its properties and how it is used. Thus, learning to comprehend and produce language involves phonological, semantic, syntactic, and pragmatic development, as well as metalinguistic knowledge about language. The same factors are involved in learning a sign language, in which the basic linguistic elements are gestures rather than sounds. There are over 200 sign languages, including American Sign Language (ASL), which are based on gestures, both manual and facial. They are true languages, and the course of acquisition of a sign language is remarkably similar to that of a spoken language. As you will see, research on the development of sign language has provided a great deal of insight into the nature of language acquisition in general. What Is Required for Language? What does it take to be able to learn a language in the first place? Full-fledged language is achieved only by humans, but only if they have experience with other humans using language for communication. A Human Brain The key to full-fledged language development is in the human brain. Language is a species-specific behavior, in that only humans acquire language in the normal course of development in their normal environment. Furthermore, it is speciesuniversal in that virtually all young humans learn language. It takes highly abnormal environmental conditions or relatively severe cognitive impairment to disrupt children’s language development. In contrast, no other animals naturally develop anything approaching the complexity or generativity of human language, even though they can communicate with one another. For example, birds claim territorial rights via birdsong (Marler, 1970), and vervet monkey calls reveal the presence of a predator and indicate whether the predator is a hawk or a snake (Seyfarth & Cheney, 1993). Researchers have had some success in training nonhuman primates to use complex communicative systems. One of the early efforts was a very ambitious project in which a dedicated couple raised a chimpanzee in their own home, with their own children, to see if the chimp, named Vicki, would learn to speak (Hayes & Hayes, 1951). Although Vicki clearly learned to comprehend some words and phrases, she produced virtually no recognizable words. Concluding that nonhuman primates lack the vocal apparatus for producing speech, later researchers attempted to teach them sign language. Washoe, a chimpanzee, and Koko, a gorilla, became famous for their ability to communicate with their human trainers and caretakers by manual signs (Gardner & Gardner, 1969; Patterson & Linden, 1981). Washoe could label a variety of objects and could make requests (“more fruit,” “please tickle”) and comments (“Washoe sorry”). The general consensus is that, however impressive Washoe’s and Koko’s ❚ metalinguistic knowledge ❚ an under- standing of the properties and function of language—that is, an understanding of language as language COURTESY OF THE LANGUAGE RESEARCH CENTER, GEORGIA STATE UNIVERSITY, PHOTO BY LIZ PUGH 220 Panbanisha, a bonobo chimpanzee, communicates with her caretakers by using a specially designed set of symbols that stand for a wide variety of objects, people, and actions. CHAPTER 6 DEVELOPMENT OF LANGUAGE AND SYMBOL USE “utterances” were, they do not qualify as language, because they contained little evidence of syntactic structure (Terrace, Petitto, Sanders, & Bever, 1979; Wallman, 1992). The most successful sign-learning nonhumans are Kanzi and Panbanisha, two great apes of the bonobo species. Kanzi learned to communicate with humans by using a specially designed keyboard composed of numerous symbols that denote specific objects and actions (“give,” “eat,” “banana,” “hug,” etc.) (Savage-Rumbaugh et al., 1993). Kanzi became very adept at using the keyboard to answer questions, to make requests, and even to offer comments. He often combines signs, but whether they can be considered syntactically structured sentences is not clear. Kanzi also understands many words and phrases spoken to him by his human caretakers, and he is even sensitive to word order. For example, when asked to “give the shot [a syringe] to Liz” (a caretaker), he handed the syringe to her; however, when instructed to “give Liz a shot,” he touched the syringe to her arm. Whatever the ultimate decision regarding the extent to which Kanzi, Panbanisha (shown in the photo), or other nonhuman primates should be credited with language, several things are clear. Even the most basic language achievements of nonhuman primates come only after a great deal of concentrated effort by humans to teach the animals, whereas human children master the rudiments of their language by the age of 5 with little explicit teaching. At age 5, human children understand thousands of words, whereas nonhuman primates have relatively small vocabularies. Furthermore, although the most advanced nonhuman communicators combine symbols in utterances, there is little evidence for syntactic structure, which is a defining feature of language (Tomasello, 1994). In short, only the human brain acquires a communicative system with the complexity, structure, and generativity of language. Brain–language relations A vast amount of research has examined brain–language relations. One thing that is clear is that language processing involves a substantial degree of functional localization. At the broadest level, there are hemispheric differences in language functioning that we discussed to some extent in Chapter 3. For the 90% of people who are right-handed, language is primarily represented and controlled by the left hemisphere of the cerebral cortex. This association was first formally reported in 1861 by Paul Broca, a French physician, whose observations of language deficits in patients with various forms of brain injuries led him to conclude that “we speak with the left hemisphere.” Developmental evidence for language specialization in the left hemisphere also comes from EEG studies showing that, for both adults and children, listening to speech is associated with greater electrical activity in the left hemisphere than in the right. The same is true for young infants, who show greater left-hemisphere activity when listening to speech but greater right-hemisphere response to nonspeech sounds (Molfese & Betz, 1988). Thus, the left hemisphere shows some specialization for language (or language-like stimuli) at a very early age, with the degree of hemispheric specialization for language increasing over time (Mills, Coffey-Corina, & Neville, 1997; Witelson, 1987). Specialization for language is also evident within the left hemisphere (Figure 6.1). Aphasia, the condition in which language functions are severely impaired, can result from damage to some, but not other, parts of the left hemisphere. One form, Broca’s aphasia, is typically associated with injury to Broca’s area in the front part of the left hemisphere, near the motor cortex. Patients with Broca’s aphasia have 221 LANGUAGE DEVELOPMENT Motor cortex Wernicke’s area FIGURE 6.1 Lateralization of language In most Broca’s area Auditory cortex people, language is primarily represented in the left hemisphere of the cerebral cortex. Damage to Broca’s and Wernicke’s areas can produce severe impairments in language functions, known as aphasia. difficulty producing speech; they may say a single word over and over or haltingly produce short strings of words with little or no grammatical structure, as in this example: Yes . . . ah . . . Monday . . . and Dad . . . er . . . hospital . . . and ah . . . Wednesday . . . Wednesday, nine o’clock . . . and oh . . . Thursday . . . ten o’clock, ah doctors . . . two . . . an’ doctors . . . and er . . . teeth . . . yah. (Goodglass, 1979, p. 256) A different aphasia, Wernicke’s aphasia (named for the nineteenth-century neurologist who first described it), is typically associated with damage in an area next to the auditory cortex (Wernicke’s area). Patients with this type of aphasia have no trouble producing speech, but what they say makes no sense, and their language comprehension is also impaired. I feel very well. My hearing, writing has been doing well. Things that I couldn’t hear from. In other words, I used to be able to work cigarettes I didn’t know how . . . Chesterfeela, for 20 years I can write it. (Goodglass, 1993, p. 86) Left-hemisphere damage produces aphasia in deaf signers just as it does for users of spoken language. This suggests that the left hemisphere is actually specialized for the kind of analytic, serial processing required for language, not for the specific modality (spoken words or signs) in which it is expressed (Bellugi, Poizner, & Klima, 1989). Critical period for language development A considerable body of evidence has given rise to the hypothesis that the early years constitute a critical period during which language develops readily. After this period (sometime between age 5 and puberty), language acquisition is much more difficult and ultimately less successful. Relevant to this hypothesis, there are several reports of children who failed to develop language after being deprived of early linguistic input. The most famous case is that of Victor, the “Wild Child,” who had apparently been abandoned by his parents and had lived on his own for many years in the woods near Aveyron, France. When discovered in 1800, the boy, who appeared to be around 12 years of age, was naked, sometimes walked on all fours, and was frightened of people. Although he could make various sounds, he had no language. ❚ critical period for language ❚ the time during which language develops readily and after which (sometime between age 5 and puberty) language acquisition is much more difficult and ultimately less successful 222 CHAPTER 6 DEVELOPMENT OF LANGUAGE AND SYMBOL USE COURTESY OF HELEN NEVILLE, PSYCHOLOGY DEPARTMENT, UNIVERSITY OF OREGON After a number of years of intense socialization and language training, Victor learned to behave appropriately in social situations most of the time, but he never learned more than a few words (Lane, 1976). A modern-day “wild child,” Genie, came to light in the United States in 1970. From the age of approximately 18 months until she was rescued at age 13, Genie’s parents had kept her tied up and locked alone in a room. During her imprisonment, no one spoke to her; when her father brought her food, he growled at her like an animal. At the time of her rescue, Genie’s development was stunted— physically, motorically, and emotionally—and she could barely speak. With intensive training, she made some progress, but her language ability never developed much beyond the level of a toddler’s: “Father take piece wood. Hit. Cry” (Curtiss, 1977, 1989; Rymer, 1993). Do the extraordinary cases of these two children support the critical-period hypothesis? Possibly, but it is difficult to know for sure. It could be that Victor was retarded from infancy and was abandoned for that reason. Genie’s failure to develop language might have resulted as much from the bizarre Bilinguals and inhuman treatment she suffered as from the linguistic Grammatical Processing communication deprivation. Other areas of research provide much stronger evidence Age of 2nd language for the critical-period hypothesis. As noted in Chapter 3, acquisition adults, who are well beyond the critical period, are more likely to suffer permanent language impairment from brain 1–3 years damage than are children, presumably because other areas of the young brain (but not the older one) are able to take over language functions (see Johnson, 1998). (See Chapter 3, pages 114–115 to review the role of timing in the long-term effects of brain damage.) Additional strong support for the critical-period hypothesis comes from studies of adults who learned a second lan4–6 years guage at different ages. Research by Helen Neville and her colleagues (Neville & Bavelier, 1999; Weber-Fox & Neville, 1996) has shown different patterns of cerebral organization in late learners of a second language and in those who learned it early. As Figure 6.2 shows, people who learned English at 4 years of age or later showed less left-hemisphere 11–13 years localization of those aspects of brain organization related to grammatical processing in English than did people who learned the language at a younger age. In a very important behavioral study, researchers tested the English proficiency of Chinese and Korean immigrants Left Right who had come to the United States and had begun learning FIGURE 6.2 Hemispheric differences in English either as children or as adults ( Johnson & Newport, 1989). The results, language processing Adults who learned a shown in Figure 6.3, reveal that knowledge of some fine points of English gramsecond language at 1 to 3 years of age mar was related to the age at which these individuals began learning English, but (top pair of images) show the normal pattern of greater activity in the left hemisphere not to the length of their exposure to the language (i.e., how long they had been during a test of grammatical knowledge. in America). The most proficient were those who had begun learning English (Darker colors indicate greater activation.) before the age of 7. The same pattern of results has been described for the learnThose who learned the language later ing of one’s first language. Similarly, the ASL proficiency of deaf adults depends show less localized activity, including on the age at which they first started learning it—the earlier they began, the more more right-hemisphere activity. skilled they were as adults (Newport, 1990). (Adapted from Neville & Bavelier, 1999) 223 LANGUAGE DEVELOPMENT 270 260 250 240 230 220 210 A Human Environment Possession of a human brain is not enough for language to develop. Children must also be exposed to other people using language—any language, signed or spoken. Adequate experience hearing others talk is readily available in the environment of almost all children anywhere in the world ( Jaswal & Fernald, 2002). Like Benjamin watching his parents do the dinner dishes (Chapter 5), infants and young children overhear countless conversations, and in most societies, some speech is specifically directed to them. Much of the speech directed to infants occurs in the context of daily routines—during thousands of mealtimes, diaper changes, baths, and bedtimes, as well as in countless games like peekaboo and “eentsie-weentsie spider.” Infants apparently identify speech as something important very early: infants 2 months of age pay attention longer to speech sounds than to nonspeech (Vouloumanos & Werker, 2004). Infant-directed talk Imagine yourself on a bus; behind you, someone is talking to another person. Could you guess whether that person was addressing an infant or an adult? We have no doubt that you—or anyone else—could, even if you were in another country where you didn’t speak the local language. The reason is that in virtually all societies, adults adopt some distinctive mode of speech when talking to babies and very young children. This special way of speaking was originally dubbed “motherese” (Newport, Gleitman, & Gleitman, 1977), but the current term infant-directed talk (IDT) recognizes the fact that this special style of speech is not used just by mothers. Indeed, even young children adopt it when talking to babies (Shatz & Gelman, 1973). As we describe the characteristics of IDT, keep in mind that it is not used in all cultures and that the IDT of American mothers tends to be more extreme than that of virtually any other group (Fernald, 1989). CHARACTERISTICS OF INFANT-DIRECTED TALK Possibly the most obvious quality of speech directed toward infants is its emotional tone. It is speech suffused with affection—“the sweet music of the species,” as Darwin (1877) put it. Another obvious characteristic of IDT is exaggeration (see Boysson-Bardies, 1999). People talking to babies do so in a much higher voice than they Native 3–7 8–10 11–15 17–39 Age (in years) at arrival FIGURE 6.3 Test of critical-period hypothesis Performance on a test of English grammar of adults originally from Korea and China is directly related to the age at which they came to the United States and were first exposed to English. The scores of adults who emigrated before the age of 7 are indistinguishable from those of native speakers of English. (Adapted from Johnson & Newport, 1989) ❚ infant-directed talk (IDT) ❚ the distinctive mode of speech that adults adopt when talking to babies and very young children The infant-directed talk used by this father grabs and holds his baby’s attention. MICHAEL NEWMAN / PHOTOEDIT Mean score Elissa Newport (1991) proposed an intriguing hypothesis for these results and for why children are generally better language learners than adults. According to her “less is more” account, perceptual and memory limitations cause young children to extract and store smaller chunks of the language they hear than adults do. Because it is far easier to figure out the underlying structure of shorter samples of speech than longer ones, young learners’ limited cognitive abilities may actually make the task of analyzing and learning language easier. The evidence for a critical period in language acquisition has some very clear practical implications. For one thing, deaf children should be exposed to sign language as early as possible. For another, foreignlanguage training in the schools, discussed in Box 6.1, should begin in the early grades; by the time students reach high school, their languagelearning capability has already declined. 224 CHAPTER 6 DEVELOPMENT OF LANGUAGE AND SYMBOL USE applications Two Languages Are Better Than One ELIZABETH CREWS / THE IMAGE WORKS The topic of bilingualism, the ability to use two languages, has attracted substantial attention in recent years as increasing numbers of children are developing bilingually. Indeed, almost half of the children in the world are regularly exposed to more than one language, and some children begin learning two languages very early in life, often because their parents have different native languages. Does early exposure to two languages cause confusion and make the task of language learning more difficult? Research on bilingual acquisition gives little cause for concern. For the most part, children who are acquiring two languages do not seem to confuse them; indeed, they appear to build two separate linguistic systems (deHouwer, 1995). They do not mistakenly use the phonological system of one language to pronounce words in the other. Although a word from one language may occasionally get mixed into a sentence in ❚ bilingualism ❚ the ability to use two languages the other, children keep the grammatical rules of the two languages separate. Learning two languages is, of course, more work than learning just one, and children developing bilingually may initially lag behind slightly on some language measures (Oller & Pearson, 2002). However, both the course and the rate of development are generally very similar for bilingual and monolingual children (deHouwer, 1995). In addition, there are cognitive benefits to bilingualism: children who are competent in two languages perform better on a variety of cognitive tests than do monolingual children (Bialystok, 2009; Bialystok, Shenfield, & Codd, 2000). Thus, the advantages of acquiring two languages outweigh the minor disadvantages. More difficult issues arise with respect to formal acquisition of a second language later on in school. A major debate in many countries, including the United 6.1 States and France, has centered around bilingualism in the classroom and what approach to take in educating school-age children who are not fluent in the dominant language of the country. The debate over bilingual education in the United States is extremely complicated and tied up with a host of political, ethnic, and racial issues. One side of this debate advocates total immersion, in which children are communicated with and taught exclusively in English, with the goal of helping them become proficient in English as quickly as possible. The other side recommends an approach that initially provides children with instruction in basic subjects in their native language and gradually increases the amount of instruction provided in English. In support of the latter view, there is evidence that (1) children often fail to master basic subject matter when it is taught in a language they do not fully understand; and (2) when both languages are integrated in the classroom, children learn the second language more readily, participate more actively, and are less frustrated and bored (Augusta & Hakuta, 1998; Crawford, 1997; Hakuta, 1999). This approach also helps prevent semilingualism—inadequate proficiency in both languages—which can occur if children become less proficient in their original language as a result of being taught a second one in school. The issue of bilingualism in the classroom has been a topic of intense debate in the United States and other parts of the world. However, research conducted by Ellin Bialystok in areas such as Montreal, where a substantial proportion of the population speak both English and French, reveal a variety of benefits of proficiency in multiple languages. would ever use with an adult (except possibly a lover), and they make extreme changes in intonation patterns, swooping abruptly from very high-pitched sounds to very low ones. They also talk more slowly and clearly and elongate the pauses between their utterances. All this exaggerated speech is accompanied by exaggerated facial expressions. Many of these characteristics have been noted in adults speaking such languages as Arabic, French, Italian, Japanese, Mandarin Chinese, and Spanish (see Boysson-Bardies, 1999), as well as in deaf mothers signing to their infants (Masataka, 1992). Although the prevalent emotional tone of IDT is warm and affectionate, parents of older infants vary it to impart important information. For example, a mother’s “No” uttered with sharply falling intonation tells the baby that the mother disapproves of something, whereas a cooed “Yeesss” indicates approval. The same intonational qualities are used by mothers to signal approval and disapproval across languages, from English to Italian to Japanese (Fernald et al., 1989). That infants use the intonation of their mothers’ messages to interpret meaning was clearly established by Anne Fernald (1989) in a series of clever experiments. In one, 8-month-old infants were presented with an attractive toy, and their mothers either said “Yes, good boy” or “No, don’t touch.” Half the statements of each type were said in a cooing, encouraging tone of voice and half were said in a sharp, prohibitive tone. The infants played with the toy more when their mother’s tone of voice was encouraging, regardless of what she actually said. Do infants care how they are spoken to? They seem to. In fact, they prefer IDT to speech directed at an adult—even when IDT is spoken to an infant other than themselves (Cooper & Aslin, 1994; Pegg, Werker, & McLeod, 1992) and even when it is in a language other than their own. For example, in one study, both Chinese and American infants listened longer to a Cantonese-speaking Chinese woman talking to a baby than to the same woman talking to an adult friend (Werker, Pegg, & McLeod, 1994). Furthermore, infants (and even adults) learn new words better, whether in their native language or in a foreign one, when the words are presented in IDT than when they are presented in adult-directed speech (Golinkoff & Alioto, 1995; Golinkoff, Alioto, & Hirsch-Pasek, 1996). As previously noted, although IDT is very common throughout the world, it is not universal. Among the Kwara’ae of the Solomon Islands in the South Pacific (Watson-Gegeo & Gegeo, 1986), the Kaluli of New Guinea (Schieffelin & Ochs, 1987), and the Ifaluk of Micronesia (Le, 2000), for example, it is believed that infants lack any capacity for understanding speech and that there is therefore no point in speaking to them. When Kaluli infants begin to speak, showing some language understanding, their parents initiate very direct language training, saying words or sentences and instructing their child to repeat what they just said. Crosslinguistic research indicates that whether parents speak directly to their infants or not may affect the speed of their early language learning, but not the level of mastery they eventually achieve (Lieven, 1994). We thus see that infants begin life equipped with the two basic necessities for acquiring language: a human brain and a human environment. So long as they do not suffer from serious brain injury or developmental disorders or grow up in conditions of extreme social deprivation, they will acquire their native language. We turn now to the many steps through which that remarkable accomplishment proceeds. The Process of Language Acquisition Acquiring a language involves both listening and talking (or looking and signing); it requires both comprehending what other people communicate to you and producing intelligible language of your own. Infants start out paying attention to what people say or sign, and they know a great deal about language long before their first linguistic productions. 225 BOB AND IRA SPRING / STOCK CONNECTION / PICTUREQUEST LANGUAGE DEVELOPMENT Around the world, parents in some cultures talk directly to their babies, whereas parents in other cultures do not. Almost everywhere, adults and older children use some form of “baby talk” to address infants. 226 ❚ prosody ❚ the characteristic rhythm, tempo, cadence, melody, intonational patterns, and so forth with which a language is spoken ❚ categorical perception ❚ the perception of speech sounds as belonging to discrete categories ❚ voice onset time (VOT) ❚ the length of time between when air passes through the lips and when the vocal cords start vibrating DEVELOPMENT OF LANGUAGE AND SYMBOL USE CHAPTER 6 Speech Perception The first step in language learning is the perception of speech. As you saw in Chapter 2, the task usually begins in the womb, as fetuses develop a preference for their mother’s voice and the language they hear her speak. The basis for this very early learning is prosody, the characteristic rhythm, tempo, cadence, melody, and intonational patterns with which a language is spoken. Differences in prosody are in large part responsible for why languages—from Japanese to French to Swahili— sound so different from one another. Prosody also accounts for why speakers of the same language can sound so different. Contrast the highly expressive speech of British speakers, for example, with the relatively flat speech of Americans. Beyond prosody, speech perception also involves distinguishing among the speech sounds that make a difference in a given language. To learn English, for example, one must distinguish between bat and pat, dill and kill, Ben and bed. Remarkably, infants do not have to learn to hear these differences; young infants perceive many speech sounds in very much the same way that adults do. Categorical perception of speech sounds Both adults and infants perceive speech sounds as belonging to discrete categories. This phenomenon, referred to as categorical perception, has been established by studying people’s response to artificial speech sounds. In this research, a speech synthesizer is used to gradually and continuously change one speech sound, such as /b/, into a related one, such as /p/. These two phonemes are on an acoustic continuum; they are produced in exactly the same way, except for one crucial difference—the length of time between when air passes through the lips and when the vocal cords start vibrating. This lag, referred to as voice onset time (VOT), is much shorter for /b/ (15 milliseconds) than for /p/ (100 ms). (Try saying “ba” and “pa” alternately several times, and you will likely experience what VOT refers to.) Researchers create tape recordings of artificial speech sounds that vary along this VOT continuum, so that each successive sound is slightly different from the one before, with /b/ gradually changing into /p/. However, adult listeners do not perceive this continuously changing series of sounds (Figure 6.4). Instead, they hear /b/ repeated several times and then hear an abrupt switch to /p/. All the sounds in this continuum that have a VOT of less than 25 ms are perceived as /b/, and all those that have a VOT greater than 25 ms are perceived as /p/. Thus, adults automatically divide the continuous signal into two discontinuous categories—/b/ and /p/. FIGURE 6.4 Categorical perception of speech sounds by adults When adults listen to a tape of artificial speech sounds that gradually change from one sound to another, such as /ba/ to /pa/ or vice versa, they suddenly switch from perceiving one sound to perceiving the other. (Adapted from Wood, 1976) Percentage of responses /ba/ or /pa/ 100 80 /pa/ 60 40 /ba/ 20 0 –50 –40 –30 –20 –10 0 10 20 Voice onset time (ms) 30 40 50 60 70 227 LANGUAGE DEVELOPMENT Mean number of sucking responses FIGURE 6.5 Categorical perception of Young babies make the same kind of sharp distinctions between speech sounds. speech sounds by infants One- and fourThis remarkable fact was established using the habituation technique familiar to month-old infants were habituated to a tape you from previous chapters. In the original, classic study (one of the 100 most freof artificial speech sounds. (a) One group quently cited studies in psychology), 1- and 4-month-olds sucked on a pacifier repeatedly heard a /ba/ sound with a VOT hooked up to a computer (Eimas et al., 1971). Their sucking caused speech sounds of 20, and they gradually habituated to it. to be played for them to listen to. After hearing the same sound repeatedly, the ba(b) When the sound changed to /pa/, with a VOT of 40, they dishabituated, indicating that bies gradually sucked less enthusiastically. Then a new sound was played. If the inthey perceived the difference between the fants’ sucking response to the new sound increased, the researchers inferred that two sounds, just as adults do. (c) A different the infants discriminated the new sound from the old one. group was habituated to a /pa/ sound with a The crucial factor in this study was the relation between the new and old VOT of 60. (d) When the sound changed to sounds—specifically, whether they were from the same or different adult phoneanother /pa/ with a VOT of 80, the infants remained habituated, suggesting that, like mic categories. For one group of the babies, the new sound was from a different adults, they did not discriminate between adult category; thus, after habituation to a series of sounds that adults perceive as these two sounds. (Adapted from Eimas /b/, sucking now produced a sound that adults identify as /p/. For the second et al., 1971) group, the new sound was within the same category as the old one (i.e., adults perceive them both as /b/). A (a) (b) (c) (d) critical feature of the study is that for both groups, the VOT = 20 VOT = 40 VOT = 60 VOT = 80 new and old sounds differed equally in terms of VOT. As Figure 6.5 shows, after habituating to /b/, the in60 fants increased their rate of sucking when the new sound came from a different phonemic category (/p/ in45 stead of /b/). Habituation continued, however, when the new sound was within the same category as the original one. Since this classic study, researchers have established 30 that infants show categorical perception of numerous speech sounds (Aslin, Jusczyk, & Pisoni, 1998). 15 One difference between infants’ and adults’ distinction among speech sounds, however, is that young infants actually make more distinctions than adults do. B 5 4 3 2 1 1 2 3 4 B 5 4 3 2 1 1 2 3 4 This rather surprising phenomenon occurs because all Time (min) languages use only a subset of the large variety of phonemic categories that exist. As noted earlier, the sounds /r/ and /l/ make a difference in English, but not in Japanese. Similarly, speakers of Arabic, but not of English, perceive a difference between the /k/ sounds in “keep” and “cool.” Adults simply do not perceive most differences in speech sounds that are not important in their native languages, which partly accounts for why it is so difficult for adults to become fluent in a second language. In contrast, infants can distinguish between phonemic contrasts made in all the languages of the world—about 600 consonants and 200 vowels (Tsao, Liu, & Kuhl, 2004). Research shows that, for example, Kikuyu infants in Africa are just as good as are American babies at discriminating English contrasts not found in Kikuyu (Streeter, 1976). Studies done with infants from English-speaking homes have shown that they can discriminate non-English distinctions made in languages ranging from German and Spanish to Thai, Hindi, and Zulu ( Jusczyk, 1997). This research reveals an ability that is both innate, in the sense that it is present at birth, and independent of experience, because infants can discriminate between speech sounds they have never heard before. Presumably, this capacity for categorical perception of speech sounds is enormously helpful to infants, because it essentially primes them to start learning whichever of the world’s languages they hear around them. The crucial role of early speech perception in learning language is reflected in a relation between infants’ speech perception skills and their later 228 CHAPTER 6 DEVELOPMENT OF LANGUAGE AND SYMBOL USE FIGURE 6.6 Speech perception This infant is participating in a study of speech perception in the laboratory of Janet Werker. The baby has learned to turn his head to the sound source whenever he hears a change from one sound to another. A correct head turn is rewarded by an exciting visual display, as well as by the applause and praise of the experimenter. To make sure that neither the mother nor the experimenter can influence the child’s behavior, they are both wearing headphones that prevent them from hearing what the baby hears. (From Werker, 1989) FIGURE 6.7 Percent of infants able to discriminate foreign-language speech sounds Infants’ ability to discriminate between speech sounds not in their native language declines between 6 and 12 months of age. Most 6-month-olds from English-speaking families readily discriminate between syllables in Hindi (blue bars) and Nthlakapmx (green bars), but most 10- to 12-month-olds do not. (Adapted from Werker, 1989) Developmental changes in speech perception The ability of young infants to discriminate among speech sounds they have never heard before does not last long. By the end of their first year, their speech perception is similar to that of their parents. The initial demonstration of this shift was carried out by Janet Werker and her colleagues, who tested the ability of infants of different ages to discriminate speech sounds (Werker, 1989; Werker & Lalonde, 1988; Werker & Tees, 1984). The infants were all from English-speaking homes, and they were tested with speech contrasts that are not used in English but that are important in two other languages—Hindi and Nthlakapmx (a language spoken by North American Indians in the Pacific Northwest). To test the discriminatory capabilities of 6- to 12-month-old infants, the researchers used a simple conditioning procedure, shown in Figure 6.6. The infants learned that whenever they heard a change in the series of sounds they were listening to, they could see an interesting sight by turning their head to one side. Thus, discrimination between the speech sounds was inferred if the infants quickly turned their heads in the correct direction following a sound change. Figure 6.7 shows that at 6 to 8 months of age, the infants readily discriminated between the sounds they heard; they could tell one Hindi syllable from another, and they could also distinguish between two sounds in Nthlakapmx. At 10 to 12 months of age, however, the infants no longer perceived the differences they had detected a few months before. Two Hindi syllables that had previously sounded different to them now sounded the same. A similar change occurs slightly earlier for vowels (Kuhl, 1991; Kuhl, Williams, Lacerda, Stevens, & Lindbloom, 1992; Polka & Werker, 1994). Thus, infants are born with the ability to discriminate between speech sounds in any language, but they gradually begin to specialize, retaining their sensitivity to sounds in the language they hear every day—their native language—but becoming increasingly less sensitive to nonnative speech sounds. This change begins as early as 7 months for some infants. ERP recordings of 7-month-olds’ responses to native and nonnative phonemes revealed that some babies were already better at discriminating among sounds in their native language than in another language. Further, 100 those 7-month-olds who had begun to home in on the sounds of their native language later performed better on vocabulary 80 and grammar tests given between 14 and 30 months of age. 60 Identifying such regularities in speech sounds supports the learning of words. 40 After repeatedly hearing “twang” and “dobu” embedded in a long stream of speech sounds, 17-month-olds readily learned those 20 sounds as labels for objects. Having aleady learned the sound sequences that made 0 6–8 8–10 10–12 up the words apparently made it easier to Age (in months) associate the words with their referents (Estes & Salt, 2007). Infants able to discriminate (%) ADAPTED FROM WERKER, J.F. (1989). “BECOMING A NATIVE LISTENER.” AMERICAN SCIENTIST, 77:59. REPRINTED WITH PERMISSION OF AMERICAN SCIENTIST, JOURNAL OF SYGMA XI, THE SCIENTIFIC RESEARCH SOCIETY. PHOTOS COURTESY OF PETER MCLEOD, ACADIA UNIVERSITY language skills. Babies who were better at detecting differences between speech sounds at 6 months scored higher on vocabulary and grammar tests at 13 to 24 months of age (Tsao, Liu, & Kuhl, 2004). LANGUAGE DEVELOPMENT Sensitivity to regularities in speech In addition to focusing on the speech sounds that are used in their native language, infants become increasingly sensitive to many of the numerous regularities in that language. One example is stress pattern, an element of prosody. In English, the first syllable in two-syllable words is much more often stressed than the second syllable is (as in “English,” “often,” and “second”). Nine-month-old American infants attend longer to lists of words that follow this pattern than to words in which the second syllable is stressed ( Jusczyk, Cutler, & Redanz, 1993). The discovery that infants are sensitive to this regular feature of the language they hear was made possible through a very simple procedure designed to assess infants’ auditory preferences. Lights mounted near two loudspeakers located in panels on either side of an infant are used to draw the infant’s attention to one side or the other. As soon as the infant turns to look at the light, an auditory stimulus is played through the speaker, and it continues as long as the baby is looking in that direction. The length of time the infant spends looking at the light—and hence listening to the sound—is taken as a measure of the degree to which the infant is attracted to that sound. As you will see, this head-turn preference procedure has been used extensively to address a wide variety of questions about language development in infancy. Another regularity to which infants are surprisingly sensitive concerns the distributional properties of the speech they hear. In any language, certain sounds are more likely to appear together than are others. Sensitivity to such regularity in the speech stream was demonstrated in an elegant series of statistical-learning experiments in which babies learned new words based purely on regularities in how often a given sound followed another (Aslin, Saffran, & Newport, 1998; Saffran, Aslin, & Newport, 1996). The infants listened to a 2-minute tape of four different three-syllable “words” (e.g., tupiro, golabu, bidaku, padoti) repeated in random order with no pauses between the “words.” Then, on a series of test trials, the babies were sometimes presented with the “words” they had heard and sometimes with “nonwords”—the same syllables in different combinations. They listened longer to the novel “nonwords.” To have formed this preference, the babies must have registered that certain syllables often occurred together in the sample of speech they heard—as when “bi” was always followed by “da” and “da” was always followed by “ku,” whereas “ku” was followed by any of three other syllables (“tu,” “go,” or “pa”). Thus, the infants used recurrent sound patterns to fish words out of the passing stream of speech. Probably the most salient regularity in what infants and toddlers hear is their own name. As early as 5 months of age, they show the “cocktail party effect,” attending selectively to the sound of their own name among a stream of speech sounds they are hearing (Newman, 2005). As demonstrated in the research on speech perception we have reviewed, infants work very hard right from the beginning to identify patterns in the sounds they hear other people producing. They start out with the ability to make crucial distinctions among speech sounds but then narrow their focus to the sounds that they hear with regularity, the ones that make a difference in their native language. With increasing language exposure, infants come to identify remarkably subtle features in what they hear. 229 bidakupadotigolabubidakugolabupadotib idakupadotigolabupadotibidakupadoti… How quickly could you pick out a word from a stream of speech like the one shown here? It takes 8-month-old infants only 2 minutes of listening. Preparation for Production In their first months, babies are getting ready to talk. The repertoire of sounds they can produce is extremely limited for the first two months. They cry, sneeze, sigh, burp, and smack their lips, but their vocal tract is not sufficiently developed to allow them to produce anything like real speech sounds. Then, at around 6 to ❚ distributional properties ❚ the phenomenon that in any language, certain sounds are more likely to appear together than are others 230 CHAPTER 6 DEVELOPMENT OF LANGUAGE AND SYMBOL USE PHOTOS BY JEFFREY DEBELLE / © DR. LAURA ANN PETITTO 8 weeks of age, infants suddenly begin producing simple speech sounds—long, drawn-out vowel sounds, such as “ooohh” or “aaahh,” or consonant–vowel combinations such as “goo.” Lying in their cribs, young infants entertain themselves with vocal gymnastics, switching from low grunts to high-pitched cries, from soft murmurs to loud shouts. They click, smack, blow raspberries, squeal, all with apparent fascination and delight. Through this practice, infants gain motor control over their vocalizations. At the same time that their sound repertoire is expanding, infants become increasingly aware that their vocalizations elicit responses from others, and they begin to engage in dialogues of reciprocal ooohing and aaahing, cooing and gooing, with their parents. With improvement in their motor control of vocalization, they increasingly imitate the sounds of their “conversational” partners, even producing higher-pitched sounds when interacting with their mothers and lower-pitched sounds when interacting with their fathers (Boysson-Bardies, 1999). Babbling Sometime between 6 and 10 months of age, but on average at around 7 months, a major milestone occurs: babies begin to babble. Standard babbling involves producing syllables made up of a consonant followed by a vowel (“pa,” “ba,” “ma”) that are repeated in strings (“papapa”). Although it was formerly believed that infants babble a wide range of sounds from their own and other languages ( Jakobson, 1941), more recent research has revealed that babies actually babble a fairly limited set of sounds, although some not in their native language are included (Boysson-Bardies, 1999). A key component in the development of babbling is infants’ hearing the sounds they are producing. Although congenitally deaf infants produce vocalizations similar to those of hearing babies until around 5 or 6 months of age, their vocal babbling occurs very late and is quite limited (Oller & Eilers, 1988). (This finding is contrary to earlier claims that deaf infants begin to babble vocally at the same time as hearing babies do—e.g., Lenneberg, 1967.) However, some congenitally deaf babies do “babble” right on schedule—those who are regularly exposed to sign language. According to Petitto and Marentette (1991), at around 8 months of age, deaf infants exposed to ASL begin to babble manually, producing repetitive hand movements that are components of full ASL signs, just as vocally babbled sounds are repeated components of words. Thus, like infants learning a spoken language, deaf infants seem to experiment with the elements that are combined to make meaningful words in their native language (Figure 6.8). As their babbling becomes more varied, it gradually takes on the sounds, rhythm, and intonational patterns of the language infants hear daily. In a simple but clever experiment, French adults listened to the babbling of a French 8-month-old and an 8-month-old from either an Arabic- or Cantonese-speaking family. When asked to identify which baby was the French one in each pair, the adults chose correctly 70% of the time (Boysson-Bardies et al., 1984). Thus, before infants utter their first meaningful words, they are, in a sense, native speakers of a language. FIGURE 6.8 Silent babbling Babies who are exposed to the sign language of their deaf parents engage in “silent babbling.” A subset of their hand movements differ from those of infants exposed to spoken language in that their slower rhythm corresponds to the rhythmic patterning of adult sign. (Adapted from Petitto, Holowka, Sergio, & Osstry, 2001) LANGUAGE DEVELOPMENT 231 TONY FREEMAN / PHOTO EDIT Early interactions Before we turn to the next big step in language production— uttering recognizable words—it is important to consider the social context that promotes language development in most societies. Even before infants start speaking, they display the beginnings of communicative competence, the ability to communicate intentionally with another person. The first indication of this communicative competence is turn-taking. In a conversation, mature participants alternate between speaking and listening. Jerome Bruner and his colleagues (Bruner, 1977; Ratner & Bruner, 1978) have proposed that learning to take turns in social interactions is facilitated by parent–infant games, such as peekaboo and “Give-and-Take,” in which caregiver and baby take turns giving and receiving objects. (Infants are initially much better at offering an object than they are at relinquishing it.) In these “action dialogues” (Bruner, 1977), the child alternates between active and passive roles, just as one alternates between speaking and listening in conversations. These early interactions provide infants with a scaffold for incorporating words to communicate with others. As discussed in Chapter 4 (page 161), successful communication also requires intersubjectivity, in which two interacting partners share a mutual understanding. The foundation of intersubjectivity is joint attention, which, early on, is established by the parent’s following the baby’s lead, looking at and commenting on whatever the infant is looking at. Around 6 months of age, infants become capable of following the direction of another’s gaze, as long as the person is looking at something the infant can see. By 18 months of age, they can use the direction of an adult’s gaze to determine the location of an object (Butterworth & Grover, 1988). A sure method of establishing joint attention with another adult is to point toward whatever you want to talk about. If you try this with a young infant, however, the baby is likely to stare intently at your outstretched finger rather than at the object you are pointing to. But by around 9 months of age, most babies look in the direction in which the finger is pointing. A few months later, they begin to point themselves (Butterworth, 1998), and by 2 years of age, pointing is deliberately employed to direct the attention of another person (Moore & D’Entremont, 2001). This toddler is pointing to get his father to share his attention—to achieve intersubjectivity. Once the father identifies the focus of his child’s attention, he may even be willing to add it to the shopping cart. 232 CHAPTER 6 DEVELOPMENT OF LANGUAGE AND SYMBOL USE We have thus seen that infants take their time getting ready to talk. Through babbling, they gain some initial level of control over the production of sounds that are necessary to produce recognizable words. As they do so, they already begin to sound like their parents. Through early interactions with their parents, they develop interactive routines similar to those required in the use of language for communication. First Words Infants first learn words simply as familiar patterns of sounds without attaching any meaning to them; but then, in a major revolution, words become vehicles of meaning. Thus, infants first recognize words, and then they begin to comprehend them. Next, they begin producing some of the words they have learned. Early word recognition The initial task in learning words is picking them out of the speech stream. As noted, the first familiar sound to perceptually pop out of the language a child hears is his or her own name. Infants as young as 41⁄2 months of age will listen longer to a tape repeating their own name than to a tape of a different but similar name (Mandel, Jusczyk, & Pisoni, 1995), and a few weeks later they can pick their own name out of background conversations. This ability helps them learn new words. After hearing “It’s Jerry’s cup” a number of times, 6-month-old Jerry is more likely to learn the word cup than if he had not heard it right after his name (Bortfield, 2005). At 7 to 8 months of age, infants readily learn to recognize new words and remember them for weeks ( Jusczyk & Aslin, 1995; Jusczyk & Hohne, 1997). In general, infants are better able to identify word boundaries when they are listening to infant-directed speech rather than to normal speech, so adults’ tendency to speak differently to infants pays off (Thiessen, Hill, & Saffran, 2005). ❚ reference ❚ in language and speech, the associating of words and meaning The problem of reference Once infants can recognize recurrent units from the speech they hear, the stage is set for them to make a truly major advance. They are ready to address the problem of reference, to start associating words and meaning. Figuring out which of the multitude of possible referents is the right one for a particular word is, as the philosopher Willard Quine (1960) pointed out, a very complex problem. If a child hears someone say “bunny” in the presence of a rabbit, how does the child know whether this new word refers to the rabbit itself, to its fuzzy tail, to the whiskers on the right side of its nose, or to the twitching of its nose? That the problem of reference is a real problem is illustrated by the case of a toddler who thought “Phew!” was a greeting, because it was the first thing her mother said on entering the child’s room every morning (Ferrier, 1978). There is evidence that infants begin associating highly familiar words with their highly familiar referents at around 6 months of age; when 6-month-olds hear either “Mommy” or “Daddy,” they look toward the appropriate person (Tincoff & Jusczyk, 1999). Infants gradually come to understand the meaning of less frequently heard words, with the pace of their vocabulary-building varying greatly from one child to another. According to parents’ reports on 1,000 children in the United States, 10-month-olds’ comprehension vocabulary—the words a child understands (but may not be able to say)—ranges from 11 to 154 words (Fenson et al., 1994). REUNION DES MUSEES NATIONAUX / ART RESOURCE, NY LANGUAGE DEVELOPMENT 233 A classic problem posed by philosopher Willard Quine was how someone who does not know the word “rabbit” could figure out exactly what it refers to. The mother in this painting by Titian may be helping her child learn what “rabbit” refers to by drawing the child’s attention to the referent of the word. Early word production Gradually, infants begin to say some of the words they understand, with most producing their first words between 10 and 15 months of age. The term productive vocabulary refers to the words a child is able to say. What qualifies as a “first word”? It can be any specific utterance that the child makes consistently to refer to or to express something. Even with this loose criterion, identification of a child’s earliest few words can be problematic. For one thing, doting parents often overinterpret their child’s babbling. For another, very early words may differ from the corresponding adult form. For example, Woof was one of the first words of the boy whose linguistic progress was illustrated at the beginning of this chapter. It was used to refer to the dog next door—both to excitedly name the animal when it appeared in the neighbors’ yard and to wistfully request the dog’s presence when it was absent. Initially, infants’ early word production is limited by their ability to pronounce the words they know in a way that an attentive parent can discern their meaning. To make life easier for themselves, infants adopt a variety of simplification strategies (Gerken, 1994). For example, they leave out the difficult bits of words, turning banana into “nana,” or they substitute easier sounds for hardto-say ones—“bubba” for brother, “wabbit” for rabbit. Sometimes they reorder parts of words to put an easier sound at the beginning of the word, as in the common “pasketti” (for spaghetti) or the more idiosyncratic “Cagoshin” (the way the child quoted at the beginning of the chapter continued for several years to say Chicago). Children’s early language is subject to a number of other CHAPTER 6 DEVELOPMENT OF LANGUAGE AND SYMBOL USE individual differences Variability in Language Development Parents often become needlessly concerned if their child seems to lag behind his or her peers in reaching any of the major milestones in language development. When should they worry? It is important that parents understand that there are huge individual differences in many aspects of language acquisition, and most of them do not predict later problems. One form of variation that language researchers have identified is style, that is, the strategies young children enlist in beginning to speak. Some children display a referential or analytic style, whereas others are characterized as having an expressive or holistic style (Bates, Dale, & Thal, 1995; Bloom, 1975; Nelson, 1973). A third style is referred to as wait-and-see (Boysson-Bardies,1999). Boysson-Bardies (1999) has described these three styles using French infants as examples. Children characterized as referential tend to analyze the speech stream into individual phonetic elements and words, and their first utterances tend to be isolated, often monosyllabic words. This style is exemplified by Emilie, whose first 20 words were almost all monosyllables starting with the same three consonants that had dominated her earlier babbling. Thus, from the adult words she heard, she seemed to systematically select those beginning with the sounds she had already mastered. Her simple and efficient strategy enabled Emilie to rapidly increase her vocabulary. ❚ style ❚ the strategies that young children enlist in beginning to speak ❚ referential (analytic) style ❚ speech strat- egy that analyzes the speech stream into individual phonetic elements and words; the first utterances of children who adopt this style tend to use isolated, often monosyllabic words ❚ expressive (holistic) style ❚ speech strategy that gives more attention to the overall sound of language—its rhythmic and intonational patterns—than to the phonetic elements of which it is composed ❚ wait-and-see style ❚ speech strategy that typically involves a late start in speaking, but a large vocabulary once speaking begins Children characterized as expressive give more attention to the overall sound of language—its rhythmic and intonational patterns—than to the phonetic elements of which it is composed. This style was adopted by Simon, whose strategy might be characterized as “conversation first.” Rather than beginning with small units of speech as Emilie did, sociable Simon joined in the conversations of adults with long “sentences” or even “questions,” all uttered with perfect French intonational patterns. However, these utterances included hardly any recognizable words. Children described as “wait-and-see” begin to talk late—some of them very late. Henri babbled very little, and even after he understood many words, he rarely said anything beyond “papa,” “maman,” and “non.” Henri had, however, been listening carefully for a long time, because at the age of 20 months he suddenly began saying a large number of clearly articulated words and then rapidly acquired more. Although these different styles reflect substantial differences in how children go about beginning to talk, they have little if any effect on the ultimate outcome of the process. As noted earlier in the chapter, children also differ dramatically in the age at which they speak their first recognizable word and produce their first sentence, and the size of their early vocabularies varies widely as well. However, most young children who lag behind others or who are below average in 6.2 © BETTMANN / CORBIS 234 Parents who are concerned about their slow-to-talk child can take heart from the fact that Albert Einstein is reported not to have talked before 4 or 5 years of age. productive vocabulary—even those who are far below the norm—catch up within a few years. Therefore, as long as there are no other signs of developmental problems, parents should not worry overly much if their child is a late talker. There is cause for concern, however, about a young child whose comprehension of language is lagging, because this kind of delay may signal a hearing problem or cognitive difficulties predictive of later problems (Bates et al., 1995). factors that sometimes cause their parents concern. Some of these are discussed in Box 6.2. Once children start talking, around the end of the first year, what do they talk about? The early productive vocabularies of children in the United States include names for people, objects, and events from the child’s everyday life (Clark, 1979; Nelson, 1973). Children name their parents, siblings, pets, and themselves, as well as ecologically important objects such as cookies, juice, and balls. Frequent events and routines are also labeled—“up,” “bye-bye,” “night-night.” Important modifiers are also used—“mine,” “hot,” “all gone.” Table 6.1 reveals substantial crosslinguistic correspondence in the content of the first 10 words of children in the United States, Hong Kong, and Beijing. As the table shows, many of infants’ first words in the three societies referred to specific people or were sound effects (Tardif et al., 2008). 235 LUNN JOHNSTON PRODUCTIONS, INC. / DISTRIBUTED BY UNITED FEATURE SYNDICATE, INC. LANGUAGE DEVELOPMENT TABLE 6.1 Rank Ordered List of Earliest Words in Three Languages* English (United States) Putonghua (Hong Kong) Cantonese (Beijing) Daddy Daddy Mommy Mommy Aah Daddy BaaBaa Mommy Grandma (paternal) Bye YumYum Grandpa (paternal) Hi Sister (older) Hello?/Wei? UhOh UhOh (Aiyou) Hit Grr Hit Uncle (paternal) Bottle Hello/Wei Grab/grasp YumYum Milk Auntie (maternal) Dog Naughty Bye No Brother (older) UhOh (Aiyou) WoofWoof Grandma (maternal) Ya/Wow *Words in boldface were common across all three languages; those in italics were common for two of the languages. Source: From Tardif, T., Fletcher, P., Liang, W. L., Zhang, Z. X., Marchman, V., & Kaciroti, N. (2008). Babies’ First 10 Words. Developmental Psychology, 44(4), 929–938. 236 CHAPTER 6 DEVELOPMENT OF LANGUAGE AND SYMBOL USE Nouns predominate in the early productive vocabularies of children learning English, possibly in part because their meanings are easier to pick up from observation than are the meanings of verbs: nouns label entities, whereas verbs represent relations among entities (Gentner, 1982). In addition, the proportion of nouns in very young children’s vocabularies is related to the proportion of nouns in their mother’s speech to them (Pine, 1994); middle-class American mothers (the group most frequently studied) do much more object-labeling for their infants than do mothers in some other cultures, such as Japan (Fernald & Morikawa, 1993). Initially, infants say the words in their small productive vocabulary only one word at a time. This period of one-word utterances is referred to as the holophrastic period, because the child typically expresses a “whole phrase”—a whole idea— with a single word. “Drink” can refer to the child’s desire to have his mother pour him a glass of juice. “Juice” could, of course, refer to the very same desire. Children who produce only one-word utterances are not limited to single ideas; they manage to express themselves by stringing together successive one-word utterances. An example is a little girl with an eye infection who pointed to her eye, saying, “Ow,” and then after a pause, “Eye” (Hoff, 2001). The rate of children’s vocabulary development is influenced by the sheer amount of talk that they hear: the more speech mothers address to their toddlers, the more rapidly the children learn new words (Huttenlocher, Haight, Bryk, Seltzer, & Lyons, 1991). More highly educated mothers talk to their children more than do less-educated mothers, and their children have larger vocabularies than do the children of less-educated parents (Fenson et al., 1994; Hart & Risley, 1994; Huttenlocher et al., 1991). What young children want to talk about quickly outstrips the number of words in their limited vocabularies, so they make the words they do know perform double duty. One way they do this is through overextension—using a given word in a broader context than is appropriate, as when children use dog for any four-legged animal, daddy for any man, moon for a dishwasher dial, or hot for any reflective metal (Table 6.2). Most overextensions represent an effort to communicate rather than a lack of knowledge, as demonstrated by research in which children who overextended some words were given comprehension tests (Naigles & Gelman, 1995). In one study, for example, children were shown pairs of pictures of entities for which they generally used the same label—for instance, a dog and a sheep, both of which they normally referred to as “dog.” However, when asked to point to the sheep, they chose the correct animal. Thus, these children understood the meaning of the word sheep, but because it was not in their productive vocabulary, they used a related word that they could say to talk about the animal. TABLE 6.2 Examples of Young Children’s Overextensions of Word Meaning ❚ holophrastic period ❚ the period when children begin using the words in their small productive vocabulary one word at a time ❚ overextension ❚ the use of a given word in a broader context than is appropriate Word Referents ball ball, balloon, marble, apple, egg, spherical water tank (Rescorla, 1980) cat cat, cat’s usual location on top of TV when absent (Rescorla, 1980) moon moon, half-moon-shaped lemon slice, circular chrome dial on dishwasher, half a Cheerio, hangnail (Bowerman, 1978) snow snow, white flannel bed pad, white puddle of milk on floor (Bowerman, 1978) baby own reflection in mirror, framed photograph of self, framed photographs of others (Hoff, 2001) 237 LANGUAGE DEVELOPMENT 33 30 27 Age (in months) Word learning After the appearance of their first words, children typically plod ahead slowly, reaching a productive vocabulary of fifty or so words by around 18 months of age. Suddenly, the plodding is over, as most children begin the “vocabulary explosion,” or “word spurt” (Figure 6.9) (Benedict, 1979; Goldfield & Reznick, 1990; McMurray, 2007). Word learning shifts from first gear to overdrive, with new words being said for the first time every day. Children’s comprehension vocabulary shows similar rapid growth; from 18 months of age to the time they are in 1st grade, children are estimated to learn an average of 5 to 10 new words every day (Anglin, 1993; Carey, 1978). What accounts for the speed of young children’s word learning? When we look closely, we see that there are multiple sources of support for learning new words, some coming from the people around them, and some generated by the children themselves. 24 21 18 15 12 9 First words ADULT INFLUENCES ON WORD LEARNING In addition to using IDT, which makes word learning easier for infants, adults make word learning easier for infants by telling them the names of things in ways that highlight their meaning. For example, they put vocal stress on new words and say them in the final position in a sentence—“That’s a checchi.” Also helpful is adults’ tendency to label objects that are already the focus of the child’s attention, thereby reducing uncertainty about the referent (Masur, 1982; Tomasello, 1988; Tomasello & Farrar, 1986). Another stimulus to word learning comes from the naming games many families play with young children, asking the child to point to a series of named items— “Where’s your nose?” “Where’s your ear?” “Where’s your tummy?” Repetition also helps; young children are more likely to acquire words their parents use frequently (Huttenlocher et al., 1991). confronted with novel words whose meaning they do not know, children actively exploit the context in which the new word was used in order to infer its meaning. A classic study by Susan Carey and Elsa Bartlett (1978) demonstrated fast mapping—the process of rapidly learning a new word simply from hearing the contrastive use of a familiar word and the unfamiliar word. In the course of everyday activities in a preschool classroom, an experimenter drew a child’s attention to two trays—one red, the other an uncommon color the child would not know by name—and asked the child to get “the chromium tray, not the red one.” The child was thus provided with a contrast between a familiar term (red) and an unfamiliar one (chromium). From this simple contrast, the children inferred which tray they were supposed to get and that the name of the color of that tray was “chromium.” After this single exposure to a novel word, about half the children showed some knowledge of it a week later by correctly picking the chromium one from an array of paint chips. Some theorists have proposed that the many inferences children make in the process of learning words are guided by a number of assumptions (sometimes referred to as principles, constraints, or biases) that limit the possible meanings children entertain for a new word. For example, children expect that a given entity will have only one name, an expectancy referred to as the mutual exclusivity assumption by Amanda Woodward and Ellen Markman (1998). Early evidence for this assumption came from a study in which 3-year-olds saw pairs Vocabulary spurt Sentences Language achievement FIGURE 6.9 Language achievement On average, American children say their first word at around 13 months, experience a vocabulary spurt at around 19 months, and begin to produce simple sentences at around 24 months. However, the bars above and below these means show a substantial amount of variability in when different children achieve each of these milestones. (Adapted from Bloom, 1998) CHILDREN’S CONTRIBUTIONS TO WORD LEARNING When ❚ fast mapping ❚ the process of rapidly learning a new word simply from hearing the contrastive use of a familiar and the unfamiliar word 238 CHAPTER 6 DEVELOPMENT OF LANGUAGE AND SYMBOL USE of objects—a familiar object for which the children had a name and an unfamiliar one for which they had no name. When the experimenter said, “Show me the blicket,” the children mapped the novel label to the novel object, the one for which they had no name (Markman & Wachtel, 1988). Even 13-month-old infants do the same (Woodward, Markman, & Fitzsimmons, 1994). (See Figure 6.10a.) Markman and Woodward (Markman, 1989; Woodward & Markman, 1998) also propose that a whole-object assumption leads children to expect that a novel word refers to a whole object, rather than to a part, property, action, or other FIGURE 6.10 Pragmatic cues for word learning (a) Because this (b) This child will assume that the novel word she hears the experimenter saying applies to the novel object the experimenter is looking at, even though the child cannot see the object and is looking at a different novel object when she actually hears the word. COURTESY OF JUDY DELOACHE child already knows the name of the familiar object on the table, she will pick up the novel object when the adult asks her to “show me the blicket.” (c) This child will learn gazzer as the name of the novel object that the adult smiles at triumphantly after she had previously announced that she wanted to find “the gazzer.” aspect of the object. Thus, in the case of Quine’s rabbit problem, the whole-object assumption results in children’s taking “bunny” to apply to the whole animal, not just to its tail or the twitching of its nose. In addition to their general tendency to map novel words onto novel objects, children pay attention to the social context in which language is used, exploiting a variety of pragmatic cues for word learning. For example, children use an adult’s focus of attention as a cue to word meaning. In a study by Dare Baldwin (1993), an experimenter showed 18-month-olds two novel objects and then concealed them in separate containers. Next, the experimenter peeked into one of the containers and commented, “There’s a modi in here.” The adult then removed and gave both objects to the child. When asked for the “modi,” the children picked the object that the experimenter had been looking at when saying the label. Thus, the infants used the relation between eye gaze and labeling to learn a novel name for an object before they had ever seen it (see Figure 6.10b). Another pragmatic cue that children use to draw inferences about a word’s meaning is intentionality (Tomasello, 2007). For example, in one study, 2-year-olds heard an experimenter announce, “Let’s dax Mickey Mouse.” The experimenter then performed two actions on a Mickey Mouse doll, one carried out in a coordinated and apparently intentional way, followed by a pleased comment (“There!”), and the other carried out in a clumsy and apparently accidental way, followed by an exclamation of surprise (“Oops!”). The children interpreted the novel verb dax as referring to the action the adult seemed to have intended to do (Tomasello & Barton, 1994). Similarly, 18-month-olds can even use an adult’s emotional response to infer the name of a novel object that they cannot see (Tomasello, Strosberg, & Akhtar, 1996). In a study establishing this fact, an adult announced her intention to “find the gazzer.” She then picked up one of two objects and showed obvious disappointment with it. When she gleefully seized the second object, the children inferred that it was a “gazzer.” (Figure 6.10c depicts another case in which a child infers from an adult’s emotional expression the name of an unseen object.) The degree to which preschool children take a speaker’s intention into account is shown by the fact that if an adult labels an object in a way that conflicts with their knowledge of that object, they will nevertheless accept the label if the adult clearly used it intentionally ( Jaswal, 2004). When an experimenter simply used the label “dog” in referring to a picture of a catlike animal, preschool children were reluctant to extend the word to other catlike stimuli. They were much more willing to do so when the experimenter made it clear that he really intended his use of the unexpected label by saying, “You’re not going to believe this, but this is actually a dog.” In general, children’s readiness to accept what an adult tells them supports the acquisition of information through reliance on the “testimony” of other people (Harris, 2002; Jaswal, 2004). In learning new words, young children also use the linguistic context in which novel words appear to help infer their meaning. In one of the earliest experiments on language acquisition, Roger Brown (1957) established that the grammatical form of a novel word influences children’s interpretation of it. He showed preschool children a picture of a pair of hands kneading a mass of material in a container (Figure 6.11). The picture was described to one group of children as “sibbing,” to another as “a sib,” and to a third as “some sib.” The children subsequently interpreted the new word sib as referring to the action, the container, or the material, 239 COURTESY OF JEAN BRIGGS LANGUAGE DEVELOPMENT This young Inuit child is playing a naming game; her mother has just asked her to point to her nose. ❚ pragmatic cues ❚ aspects of the social context used for word learning COURTESY OF BRIAN KOVALESKI 240 FIGURE 6.11 Linguistic context When Roger Brown, a pioneer in the study of language development, described this picture as “sibbing,” “a sib,” or “some sib,” preschool children made different assumptions about the meaning of “sib.” CHAPTER 6 DEVELOPMENT OF LANGUAGE AND SYMBOL USE depending on which grammatical form (verb, count noun, or mass noun) of the word they had heard. Two- and three-year-old children also use the grammatical category of novel words to help interpret their meaning (e.g., Hall, Waxman, & Hurwitz, 1993; Markman & Hutchinson, 1984; Waxman, 1990). Hearing “This is a dax” applied to an object, they assume that dax refers to that object, as well as to other members of the same category. In contrast, hearing “This is a dax one,” they assume that dax refers to a property of the object (e.g., its color or texture). These noun-category and adjective-property linkages are even made by infants and toddlers (e.g., Waxman & Hall, 1993; Waxman & Markow, 1995, 1998). Novel nouns particularly heighten children’s attention to shape, possibly because shape is a good cue to category membership. Children readily extend a novel noun to novel objects of the same shape, even when those objects differ dramatically in size, color, and texture (Landau, Smith, & Jones, 1988; Smith, Jones, & Landau, 1992). Thus, a child who hears a U-shaped wooden block called “a dax” will assume that dax also refers to a U-shaped object covered in blue fur or to a Ushaped piece of red wire but not to a wooden block of a different shape (Figure 6.12). A shape bias is also evident in young children’s spontaneous extension of familiar words to nonsense objects that are vaguely similar to familiar entities (e.g., a cone might be referred to as a “mountain”) (Samuelson & Smith, 2005). Children also use the grammatical structure of whole sentences to figure out meaning—a strategy referred to as syntactic bootstrapping (Fisher, 2000; Fisher, Gleitman, & Gleitman, 1991; Yuan & Fisher, 2009). An early demonstration of this phenomenon involved showing 2-year-olds a videotape of a duck using his left hand to push a rabbit down into a squatting position while both animals waved their right arms in circles (Figure 6.13) (Naigles, 1990). (The roles of the rabbit and duck were played by adults in costumes.) As they watched, some children were told “The duck is kradding the rabbit”; the others were told “The rabbit and the duck are kradding.” All the children then saw two videos side by side, one showing the duck pushing on the rabbit and the other showing both animals waving their arms in the air. Instructed to “Find kradding,” the two groups looked at Exemplar the event that matched the syntax they had heard while watching the initial video. Those who had heard the first sentence had apparently taken “kradding” to mean Shape what the duck had been doing to the rabbit, whereas change those who had heard the second sentence thought it .50 Texture change FIGURE 6.12 Shape bias In one of many studies of the shape bias, .76 ❚ syntactic bootstrapping ❚ the strategy of using the grammatical structure of whole sentences to figure out meaning Size change .82 children were shown the exemplar at the top of this figure and told that it was a “dax” (or some other nonsense word). Then they were asked which of the objects below the exemplar was also a “dax.” The numbers under the objects indicate the proportion of children who thought each object was a “dax.” As you can see, they most often thought that the word referred to the object that was of the same shape as the exemplar, even if the surface texture or size was different. (Adapted from Landau, Smith, & Jones, 1988) meant what both animals had been doing. Thus, the children had arrived at different interpretations for a novel verb depending on the structure of the sentence in which it was embedded. As you can see, infants and young children have a remarkable ability to learn new words as object names. Interestingly, they are equally able to learn nonlinguistic “labels” for objects. Infants between 13 and 18 months of age map gestures or nonverbal sounds (e.g., squeaks and whistles) onto novel objects just as readily as they map words (Namy, 2001; Namy & Waxman, 1998; Woodward & Hoyne, 1999). By 20 to 26 months of age, however, they accept only words as names. In all the above examples of young children’s ability to learn new words from various kinds of information, the information was directly provided to them by an adult experimenter. However, in everyday life, children hear lots of language that is not addressed specifically to them. It turns out they can learn new words from overhearing conversations between other people (e.g., hearing an experimenter introduce a novel word to another person) (Akhtar, 2005). Putting Words Together A major landmark in early language development is achieved when children start combining some words into sentences, an advance that enables them to express increasingly complex ideas. The degree to which children develop syntax, and the speed with which they do it, is what most distinguishes their language abilities from those of nonhuman primates. First sentences Most children begin to combine words into simple sentences by the end of their second year. However, in another example of comprehension preceding production, young children know something about word combinations well before they produce any. For example, 12- to 14-month-olds listen longer to sentences that have normal word order than to sentences in which word order is scrambled (Fernald & McRoberts, 1995). In another demonstration of infants’ sensitivity to word order, Kathy Hirsch-Pasek and Roberta Golinkoff (1991) presented infants with two videotaped scenes—one of a woman kissing some keys while holding up a ball and the other of the woman holding up the keys while kissing the ball. Thus, the same three elements—kissing, keys, and a ball—were present in both scenes. Yet when the infants heard the sentence “She’s kissing the keys” or “She’s kissing the ball,” they looked preferentially at the appropriate scene. Children’s first sentences are two-word combinations; their separate utterances of “More,” “Juice,” and “Drink” become “More juice” and “Drink juice.” These two-word utterances have been described as telegraphic speech because, just as in telegrams, nonessential elements are missing (Brown & Fraser, 1963). Consider the following examples of standard two-word utterances: “Read me,” “Mommy tea,” “Ride Daddy,” “Hurt knee,” “All wet,” “More boy,” “Key door,” “Andrew sleep” (Braine, 1976). These primitive sentences lack a number of elements that would appear in adult utterances, including function words (such as a, the, in), auxiliary verbs (is, was, will, be), and word endings (indicating plurals, possessives, or verb tenses). Children’s early sentences possess this telegraphic quality in languages as diverse as English, Finnish, Luo (Kenya), and Kaluli (New Guinea) (Boysson-Bardies, 1999). For young children learning languages like English, in which word order is crucial for meaning, their early, simple sentences follow a consistent word order: a child might say “Eat cookie” but would be unlikely ever to say “Cookie eat.” Many 241 LETITIA R. NAIGLES, UNIVERSITY OF CONNECTICUT LANGUAGE DEVELOPMENT FIGURE 6.13 Syntactic bootstrapping When children in Naigles’s (1990) study heard an adult describe this filmed scene as “The duck is kradding the rabbit,” they used the syntactic structure of the sentence to infer that kradding is what the duck is doing to the rabbit. ❚ telegraphic speech ❚ the term describing children’s first sentences that are generally two-word utterances 242 CHAPTER 6 DEVELOPMENT OF LANGUAGE AND SYMBOL USE theorists have cited this preservation of correct word order in young children’s early utterances as 4.20 evidence that they possess grammatical rules similar 4.10 to those that govern adult speech (e.g., Gleitman, 4.00 3.90 Gleitman, Landau, & Wanner, 1988). Others inter3.80 pret two-word utterances as governed by gram3.70 matical rules, but rules that are unique to the 3.60 3.50 language of children (Bloom, 1970; Braine, 1963). 3.40 Still others argue that the regularity of early word 3.30 combinations is primarily a matter of children’s 3.20 3.10 Eve imitating the order of words they hear in adult Adam Sarah 3.00 speech (Tomasello, 1992). 2.90 Many children continue to produce one- and 2.80 two-word utterances for some time, whereas others 2.70 2.60 quickly move on to sentences consisting of three or 2.50 more words. Figure 6.14 shows the rapid increase 2.40 in the mean length of utterances of three children 2.30 2.20 in Roger Brown’s (1973) classic study of language 2.10 development. As you can see from the figure, Eve 2.00 started her explosive increase in sentence length much 1.90 1.80 earlier than the other two children did. The length of 1.70 children’s utterances increases in part because they 1.60 begin to systematically incorporate some of the 1.50 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 elements that were missing from their telegraphic Age (in months) speech (deVilliers & deVilliers, 1973). Consider, for example, the sentence “I eating cookies,” said by FIGURE 6.14 Length of utterance The a 2-year-old. A short time before, this child might only have said “Eat cookie” to relation between age and the mean length communicate exactly the same idea. Now, however, three additional elements are of utterance for the three children—Adam, present—the first-person pronoun, the -ing ending on the verb, and the plural -s Eve, and Sarah—studied by Roger Brown. added to cookie. (Sometime soon the child will add the auxiliary verb am.) (From Brown, 1973) Once children are capable of producing four-word sentences, typically at around 21⁄2 years of age, they begin to produce complex sentences containing more than one clause (Bowerman, 1979): “Can I do it when we get home?” “I want this doll because she’s big” (Limber, 1973). Mean length of utterance (in morphemes) 4.30 PRACTICE MAKES PERFECT An important source of children’s increasing proficiency at using language is their own hard work. Toddlers actively practice their developing language skills, often in solitary practice sessions conducted in their beds before falling asleep. Ruth Weir (1962) put a microphone under her 21⁄2-year-old son’s crib and recorded his “crib talk”—his exploration and practice of a variety of grammatical forms, as in this example: Block. Yellow block. Look at the yellow block. There is the light. Where is the light? Here is the light. Grammatical rules As noted above, there is some debate regarding whether the regularity of toddlers’ word order reflects an internalization of grammatical rules. The strongest evidence in support of the idea that young children are learning the 243 LANGUAGE DEVELOPMENT grammatical rules of their language comes from their production of word endings. In English, the rules for pluralizing nouns and putting verbs into the past tense are, with some exceptions, highly regular: add -s to nouns and -ed to verbs. These simple rules suffice for the vast majority of English words. Young children follow these rules, as was established in a classic experiment by Jean Berko (1958) in which young children were shown a picture of a nonsense animal, which the experimenter referred to as “a wug.” Then a picture of two of the creatures was produced, and the experimenter said, “Here are two of them; what are they?” Children as young as 4 readily answered correctly: “Wugs.” Thus, these children created the correct plural form for a totally novel word. Other evidence that is consistent with the idea that children learn language rules comes from what they do with word formations that are exceptions to the standard rules. Take the plural of man and the past tense of go, for example. Children use the correct irregular forms of these words, saying “men” for the plural of man and “went” for the past tense of go. However, some time after they learn the appropriate regular endings, they start making occasional overregularization errors, in which they treat irregular forms as if they were regular. For example, a child who previously said “men” and “went” may begin producing novel forms such as “mans” and “goed,” as well as “foots,” “feets,” “breaked,” “broked,” and even “branged,” and “walkeded” (Berko, 1958; Kuczaj, 1977; Xu & Pinker, 1995). The following dialogue between a 21⁄2-year-old and his father illustrates this kind of error, as well as the difficulty of correcting it: Child: I used to wear diapers. When I growed up (pause) Father: When you grew up? Child: When I grewed up, I wore underpants. (Clark, 1993) Before fully mastering irregular forms, children sometimes alternate between overregularization errors and correct irregular word endings (Marcus, 1996; 2004). In this case, according to Marcus, overregulation errors occur when a child fails to retrieve from memory the correct form for a given irregular verb and hence applies the general rule by default. With experience using the language, such retrieval failures occur less frequently, and overregularization errors gradually disappear. Many syntactic rules have multiple components, and young children master them step by step. One example involves negation. The word no is a very useful tool for toddlers, and it accounts for many one-word utterances in children’s earliest speech. A little later, no is frequently combined with one or two other words to …
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