Being able to communicate using complex language, is one of the major things that sets us apart from all other species on this planet. This lecture, provides some brief introduction on how we acquire speech and language. Mastering a language requires skills in four specific areas. First, children have to learn the rules governing the structure and sequence for speech sounds. This is called the phonology of language. Next, they have to learn the way concepts are expressed in words and word combinations. This is called the semantics of language. Then follows grammar. Children learn the rules for arranging words and sentences, the syntax, but also adapting words to indicate number, tense, person, gender etc: the morphology of language. Finally, children need to learn how to engage in appropriate and effective communication and this is called the pragmatics of language. I will now shortly discuss development in each of these areas. And we start with phonology. The perception and production of speech sounds. The first challenge for an infant, is the fact that speakers subtly differ in how they produce each speech sound, even when they are all saying the same words. For instance in the Netherlands, people vary for the 'r', like rrr and rru. These sounds are quite different, but a Dutch native speaker will each time hear an 'r'. Therefore, infants need to learn to ignore some subtle differences in speech sounds because they all belong to the same category. At the same time, children also need to learn which differences in sound do point to different categories of speech sounds. These sounds categories are called phonemes. Importantly, different languages use different phonemes. For instance, Japanese does not distinguish between the 'r' and the 'l' like in raw and law, like English and Dutch do. In a similar vein, Arabic distinguishes two sounds that make the difference between the word for heart and dog, one word the mouth the other more in the throat. Which for me is a native Dutch speaker. Both sound like a 'k' and are difficult to tell apart. Infants are very sensitive to such differences in sound and initially distinguish all of them. However, as they become older and become more and more exposed to the native language their sensitivity for non-native phonemes decreases or the sensitivity for native phonemes increases. Over development between 6 - 12 months, we start to perceive variations in speech sounds that are important to the native language as categorical rather than continuous. This is called categorical speech perception. Children then also develop from universal listeners, to native listeners. Another key challenge is to recognize how clusters of speech sounds are combined into possible words even when you do not yet know what they refer to. This is difficult because most words appear in multi-word utterances where words are not separated by silences. If you do not know what language it appears to be a fast and continuous stream of sounds. When does a word start? When does it end? Children need to learn to pick up the auditory cues to segment words in sentences. One such cue regards to probabilities of adjacent sounds. Within a language, probabilities of adjacent syllables differ within and between words. And using those probabilities, children can learn to predict what are potentially words even before understanding their meaning. Obviously, infants not only listen but also produce sounds. Children usually start cooing around two months and babbling around six. Around 10 months the babbling starts to reflect sounds and intonations of their own language. But the first real words are usually produced around their first year. In all languages, the first words are the ones with the easiest sound sequences like, mama and dada. Although children probably know how words should sound, they often mispronounce them at first. In their toddler years, pronunciation improves greatly as children learn strategies to pronounce even the most difficult sounds and sound sequences. Phonological development is largely complete by age five. As children become able to distinguish words, they can start to learn their meaning: the semantics of the language. As early as six months, infants show evidence of understanding some basic words like their own name, and body parts like, hand and feet, daddy, mommy but it'll take another 6 - 12 months before children can actually say these words. Their vocabulary size rapidly increases. Between their first and sixth year, children learn the meaning of about 10,000 words. That's an average of five new words each day. And researchers have marveled about how children are able to learn the meaning of new words so fast as are usually numerous possibilities of what new words might mean. It appears, that children use several strategies to accomplish this feat. For instance children usually assume that a new word refers to a new object rather than an object they already know. Also new words are mapped very easily to accrued meaning which is refined with more experience. Another strategy, is to assume that the new word refers to an entire object rather than elements of it. So, if you would say handle while pointing at the handle of a teapot, a child who has never seen a teapot before would issue that the handle is the name for the entire teapot rather than assuming that it's the name of a part of the teapot. Perhaps unsurprisingly, the beginning vocabulary includes more object than action words. Probably because action words are more abstract. Later around the age of two and a half, children start to use labels for attributes of objects such as size, color, making their language more flexible. And in using words, children may apply them either too narrow called under extension or, more often using too widely called over extension. But as vocabulary and pragmatics improve, these mistakes disappear. And during elementary school years the vocabulary increases fourfold to about 40,000 at an average rate of 20 new words each day. Especially learning to read greatly expands the vocabulary. One idea of how vocabulary develops, is that understanding of words emerges from the joint use of multiple cues, perceptual, social, and linguistic. And infants would rely solely on perceptual cues such as parents shaking a toy and naming it, while toddlers, would use both perceptual and social cues like speakers direction of gaze and gestures to infer meaning. And as language develops further, linguistic cues like syntax and intonation presumably play an increasing role. As toddlers vocabulary increases to 200 - 250 words, they start combining meaningful words, that is producing two word utterances to express a wide variety of meaning. Only in the third year when three word sentences appear, does the word order start to follow the grammar rules of the language. Gradually, preschooler's refine and generalize early grammatical forms. The age at which specific syntactic rules are learned, depends on how available and consistent the form is in the native language. When children start producing three word sentences they also start using morphology. These are the small markers that change the meaning of words and sentences by indicating things like person, tense, gender, etc.. For instance consider how adding an 's' here or there changes the meaning of the following sentences: I walk to the book, I walk to the books. John walks to the book, John's book. At first, children may apply general rules too widely leading to over-regularization like saying gooses instead of geese. But this gradually disappear. During the school years, children master more complex grammatical structures. Finally, children need to learn the pragmatics of language. That is, how to engage in effective and appropriate communication. By the age of two, children are already capable of effective communication but in developing vocabulary and working memory limits strategies to sustain interactions and maintain a topic. As they grow older, these skills increase. Around this age, also appears the capability to understand intent even if it's not directly stated. Like when, “Honey, I almost tripped over your shoes in the hallway.” actually means, put away your shoes. This ability gradually becomes more advanced over middle childhood and it's closely linked to the development of a theory of mind. Theory of mind refers to the understanding of how mental processes like intentions, desires, beliefs, perceptions and emotions, influence behavior. Theory of mind is as vital for understanding other people's actions and intentions. Parents seem to have a particularly important role in stimulating these developments. And in a particular joint story book, reading and talking about these stories, helps development by exposing the children to rich, clear and coherent narratives. In this lecture, I provided a short overview of various aspects of language development. In the next lecture, I will focus on how language development is related to motor and cognitive development.
