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 a brief introduction on how we acquire speech and language. Mastering a language requires skills in 4 specific areas
First children have to learn the rules governing the structure and sequence of 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 in sentences, the syntax, but also adapting words to indicate number, tense, person, gender etcetera, the morphology.
Finally, children need to learn how to engage in appropriate and effective communication. This is called the pragmatics of language.
I will now shortly discuss developments in each of these areas
I will 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 in what kind of sound they use for the r. EXAMPLE. These sounds are quite different but in Dutch al mean “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 sounds do point to different categories of speech sounds. These sound categories are called phonemes. Importantly, different languages use different phonemes. For instance, Japanese does not distinguish the r and the l, like in ra and la, while English and Dutch do. In a similar vein, Arabic distinguishes two sounds that make the difference between the word for “heart” and “dog”, one more in the mouth and the other in the throat, which for me as a native Dutch speaker both sound like a “k” and are difficult to tell apart.
Infants, hoever, are very sensitive to such differences in sound and initially distinguish all of them. However, as they grow older and become more and more exposed to their native language, this sensitivity for non-native phonemes decreases while the sensitivity for native phonemes increases. Over development, between 6 to 12 months we start to perceive variations in speech sounds that are important to the native language as categorical instead of continuous. This is called categorical speech perception. Children then develop from universal listeners into 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 a language, it appears to be a fast and continuous stream of sounds. When does a word start, where does it end? Children need to learn to pick up the auditory cues to segment words in sentences. One such cue regards the probabilities of adjacent sounds. Within a language probabilities for adjacent syllables differ within and between words. 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 2 months and babbling around 6 months. Around 10 months the babbling starts to reflect sounds and intonations of their native 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 5.
As children become able to distinguish words, they can start to learn their meaning: the semantics of the language. As early as 6 months infants show evidence of understanding some basic words like their own name, body parts like ‘hand’ and ‘feet’, daddy and mommy, but it will 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. On average that’s 5 new words each day. Researchers have marveled about how children are able to learn the meaning of new words so fast, as there are usually numerous possibilities for what a new word 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 a crude meaning, which is refined with more experience. Another strategy is to assume that a new word refers to an entire object rather than an element 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 assume that handle is the name for the teapot, rather than assuming that it is the name of that 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 2,5 children start to use labels for attributes of objects such as size and color, making their language more flexible. In using words children may apply them either too narrow, called underextension, or, more often, use them too widely, called overextension. As vocabulary and pragmatics improve these mistakes disappear. During the elementary school years the vocabulary increases 4 fold, to about 40.000, at an average rate of 20 new words a day. Especially learning to read greatly expands the vocabulary.
One idea on how vocabulary develops is that understanding of words emerges from the joint use of multiple cues, perceptual, social and linguistic. Infants would rely solely on perceptual cues, such as a parent shaking a toy and naming it. Toddlers would use both perceptual and social cues, like speakers direction of gaze and gestures to infer meaning. As language develops further, linguistic cues like syntax and intonation presumably play an increasing role.
As toddlers vocabularies increase to 200 to 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 preschoolers refine and generalize early grammatical forms. The age at which specific syntactic rules are learned depends on the 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 etcetera. 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 book¬s / 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 these gradually disappear. During the school years children master more complex grammatical structures.
Finally, children need to learn the pragmatics of the language. That is, how to engage in effective and appropriate communication. By the age of 2 children are already capable of effective communication, but the developing vocabulary and working memory limit strategies to sustain interaction and maintain a topic. As they grow older these skills increase.
Around this age also appears the capability to understand intent even if it is 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 is 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 behaviors. Theory of Mind is thus vital for understanding other people’s actions and intentions.
Parents seem to have a particularly important role in stimulating these developments. In particular joint storybook 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.
