Sections include: our understanding of language, language and the brain, language disorders
Language is one of the pillars of human intellect. It is the principal way we formulate thoughts and convey them to others. It plays a role in how we analyze the world, reason, solve problems, and plan actions. It lets us convey memories of the past and beliefs about the future, engage others in thinking about events that have not taken place, and express the relationships we perceive between events.
Language is also an indispensable part of human culture. Without it, our systems of jurisprudence, commerce, science, as well as other human endeavors, could not exist in the forms we know, if at all. Without language, each person’s discoveries would die with him or her; language makes it possible for the achievements of one individual to be transmitted to the rest of the human species. Language skills are also vital to a person’s success in society. Without language, most individuals are unable to function normally in their families and communities. We celebrate when children learn to speak and read, and feel distress if a person loses these abilities because of disease or injury.
Our Understanding of Language
Before exploring how our brains deal with language, it is useful to understand what language is. Modern linguistics has taught us that language, in its essence, is a special kind of code. An ordinary code, such as those used by spies or computer programmers, consists of a set of symbols that people in the know can connect to the words and phrases in their language. When we crack such a code, we understand the encoded messages because we can translate them into a language we understand. Natural language is a different sort of code because its forms are directly related to meanings in our minds, not to another language.
The forms of language are grouped into several levels: simple words, words formed from other words, sentences, and discourse. Each of these levels of the language code pairs a certain form with some meaning. Words consist of elementary sounds: phonemes (such as a long a or a hissing s), syllables (fa, ing, and so on), tones (rising, falling, flat), and stress patterns (what syllables or sounds a speaker accents). Words refer to objects, actions, properties, and logical connections. Some words are formed by combining other, elementary words with such affixes as the sign for the past tense (usually ed in English); these words also refer to objects, actions, properties, and logical connections. Sentences consist of words grouped and organized to relate their meanings to each other to depict events and states in the world. Discourse consists of sequences of sentences, with relations between words and sentences defined in ways that tell us what the topic of the discourse is, what information is new and what is old, how the sentences relate to each other in logic and in time, and so on. We can convey these aspects of meaning using the positions of words in sentences, intonation and stress, and other structures of our language. Discourse also relies on inferences based on language users’ knowledge of the real world, including the context of statements.
Language is an intricate code, with all these types of representations interacting to determine the meaning of everything we say. That intricacy is also why language can communicate so powerfully. The same sounds appear in “You brought the cats,” “You caught the brats,” and “The ewe trots back,” but our knowledge of words tells us these statements have completely different meanings. Similarly, intonation and context help us discern what people mean when they say, “We bought a car” or “We bought a car!” or “We bought a car?”
Humans usually produce language aloud, for someone else to hear. Speech is an intricate process because each level of the language code affects the sounds that a person produces when speaking. We select our words according to what we want to talk about and whom we’re addressing. We choose a syntax to relate the words to each other, and an intonation to convey that syntax and the discourse structure. For instance, we say the word fire differently if we want to produce an exclamation (“Fire!”) or a question (“Fire?”). When we set out to voice a long sentence, we start by taking a deeper breath and speaking with a slightly higher pitch than when we start a short sentence. Thus, as soon as we begin to say a word or sentence, we both activate its form and fit that form into the discourse we intend to produce.
Our brains translate all this outgoing information into movements of the mouth, jaw, tongue, palate, larynx, and other articulators, regulating them on a millisecond-by-millisecond basis. On average, we produce about three words per second, or one sound every tenth of a second. The process of perceiving speech is equally complex because the hearer must extract all the levels of the language code from the signal, based on very subtle acoustic cues. Despite that complexity, speech is very accurate: we make only about one sound error per thousand sounds, and one word error per thousand words in speaking.
Though we usually use language in spoken form, there are other ways to use language. Many deaf individuals learn language in gestural forms, known as signing, and in fact most people who speak aloud also use some gestures in linguistic fashion. These two modes of using language develop without explicit instruction. Most babies naturally start to babble in the middle of their first year, playing with the sounds their mouths can make. Babies raised by parents who communicate through signing “babble” in sign language, trying out simple hand movements in the same way. With the encouragement of their parents and other caregivers, infants acquire more and more communication skills. Learning language is part of the cognitive development of every normal human being exposed to an adequate linguistic environment.
In addition to these two “naturally” occurring ways of using language, humans have developed written forms. Writing systems represent words: sometimes with symbols that correspond more or less to the sounds within words (as in English), sometimes with symbols that correspond to syllables (as in Japanese kana), and sometimes with symbols that correspond to entire words (as in Chinese). Written language requires instruction and conscious practice to master. It is therefore likely to have a different neurological basis from spoken and signed language. For us humans, writing serves the critical function of leaving a longlasting and portable record of the language that a person has produced.
Language and the Brain
Scientists have made systematic investigations for more than a century of how the brain learns, stores, and processes language. The task is difficult because there are no animals who have symbol systems as rich as ours. Therefore, for a long time, information about how our brains processed language could come only from studying the effects of neurological diseases. Scientists had to wait to examine the brains of language-impaired patients until after they died. This was how the nineteenth-century doctors Paul Broca and Carl Wernicke each connected an area of the brain to an element of speech. In the past decade, exciting new techniques have allowed us to picture the normal brain at work processing language. What used to take decades to learn we can now approach in months using positron-emission tomography (PET), special analyses of electroencephalograms (EEGs), functional magnetic resonance imaging (fMRI), magnetoencephalography, and other tools. (For more about these tools of brain science, see our section on learning the secrets of the brain.)
As is true for every other function, particular parts of the brain specialize in language. The brain has two roughly identical halves—the left and the right hemispheres—but we now know there are small differences in the sizes of some regions in those two halves. These differences may form the basis for the first major brain specialization for language—one hemisphere handles most of this function, a phenomenon called “lateralization.”
In about 98 percent of right-handers, the left hemisphere manages most language-processing functions. For non-right-handers (including both left-handed and ambidextrous people), language functions are far more likely to involve the right hemisphere. There is some evidence that lateralization differs in males and females: men’s brains tend to solve problems verbally in the left hemisphere, while the equivalent activity in women’s brains extends across both temporal lobes. There is also evidence that a person’s nondominant hemisphere is most involved in the next step beyond relating a word or sentence to its literal meaning; these advanced language functions include determining the emotional state of a speaker from his or her tone, and appreciating humor and metaphor.
Within the typical person’s left hemisphere, only a relatively small part of the cortex is responsible for language processing. Most of this region lies around the sylvian fissure and consists of advanced cortex. This area appears to be responsible for sign language as well as spoken language, but the way a person communicates exerts some effect: written language probably involves areas nearer the visual cortex, and sign language may recruit areas close to those related to our ability to locate objects in space. Very recent studies have also provided evidence that other parts of the left hemisphere may be involved to a lesser extent. These include regions in the inferior and anterior temporal lobe, the basal ganglia and thalamus, and motor-planning regions (the supplementary motor cortex). A part of the brain outside the cerebral hemispheres—the cerebellum—may also be active. Language is, after all, a complex, important, and wide-ranging function.
Can we be even more specific about exactly where in the brain particular language operations are carried out? Where do we activate the sounds of specific words, or compute the meaning of a sentence? Since the earliest investigations, some scientists have thought that the language region works more or less as a unit. Others have sworn by the idea that individual language operators are localized in specific parts of this region: one area generates what you say, another area processes what you hear from others, and so on. There are suggestive studies that pin specific language representations and processes to small parts of the brain, but for almost every study that supports this view, there are others that disagree. We can therefore say that it is clear that the entire brain is not involved in all language functions, and that each individual has some small regions in the brain’s language area that are involved in particular operations. But the jury is still out on the question of whether a specific function is always carried out in the same brain region for everyone.
Although being deprived of any brain or body function is difficult, diseases that affect language are especially devastating to humans. Not being able to communicate thoughts efficiently can cut us off from our livelihoods and families. It can have immense effects on our emotional states and social positions. Such disorders of language can arise as part of otherwise normal development, as happens in dyslexia. They can appear gradually, as a consequence of degenerative brain diseases such as Alzheimer’s and Parkinson’s disease, or suddenly, as in acute brain injuries and strokes. Language abilities also change with age, but these changes are much more mild than those caused by disease or injury.
For more than a century, researchers and clinicians tended to classify language disorders into a small number of syndromes that were characterized by how fluently people spoke, how accurately they could repeat statements, and whether they suffered from disturbed comprehension. We are now able to go far beyond these syndromes— to make highly specific diagnoses of what language processors are affected in a particular disorder. Language disorders can be extensive, affecting virtually all language-processing operations, or highly selective. For instance, some stroke patients have lost the ability to find the words for specific types of objects, such as fruits and vegetables, but have no problem with the words for animals and man-made objects. Others can give definitions for abstract words, but cannot list common objects’ physical features, such as the long neck of a giraffe. These isolated problems can affect any aspect of language, including reading. Some people after strokes cannot read irregular words (pint—as opposed to mint, hint, lint, etc.) but can read complex nonsense words (bleferate); others have the opposite problem. By identifying language problems more specifically, we can better help people recover from them or work around these disabilities. Studying such disorders also helps us understand normal language processing.
Parents occasionally wonder if their infants are learning to speak “on schedule.” There is in fact a wide time range within which babies learn their first words, speak their first sentences, and so on. These landmarks differ according to a number of variables, including the child’s temperament, environment, and general health. Emotion is one key to acquiring language skills; when infants hear the adults they love speaking with emotion in their voices, they seem to sense the importance of this activity and want to participate. Children can also suffer from a slow or deviant development of part of their language-processing system. Sometimes parents notice a toddler has trouble hearing sounds or discerning the separate sounds in words. This may be the sign of a hearing problem,or of a need for more structured help. A fairly common disorder appearing among school-age children is dyslexia, which affects the ability to read or write with little relation to other cognitive development. Working with special teachers can usually help a child overcome dyslexia, usually with excellent outcomes.
Because language is so much a part of our lives, a problem in communicating is usually apparent. Many adults suspect that a language problem means they or someone they know well has a disorder of the brain, but that isn’t necessarily so. The most common of these problems is difficulty finding words. This difficulty increases naturally with age, and there is a wide range of normal performance in this area. Testing by a psychologist or speech pathologist can determine whether someone’s ability to name things matches his or her age and education; only if this is not the case do those tests suggest the need for neurological investigation. Other language impairments, such as when a previously literate individual has obvious trouble reading or repeating words accurately, are relatively uncommon and demand attention.
When a person experiences a language disorder, therapy can be effective. The plasticity of our brains often allows them to work around injured areas, creating new circuits to perform the same important functions. Recent work shows that targeting specific impairments can improve language functioning. Advances in augmentative communication aids, such as specially designed computers, have allowed many patients with severe speech disorders to communicate. Even in cases in which families can expect little progress, therapy can help a person maintain and use the language he or she has.
As with every skill, exercising our language faculties leads to greater proficiency. We cannot say exactly what effect practice has on the brain— that is, what parts of our language-processing system benefit from use and how—but there is clear value in keeping the system in top shape. The language function is one of the greatest gifts of our brains.
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