Language acquisition is defined as a natural progession or development in the use of language, typified by infants and young children learning to talk. It is an unconscious process that occurs when language is used in ordinary conversation. Language acquisition is distinguished from intentional study of a language by its informality.
Theories of language acquisition
Developmental psychologists are not agreed as to how humans acquire the ability to speak their first language. It was only in the 1950s that the availability of portable tape recorders made it possible for researchers to record children's speech patterns for later analysis in the laboratory. One early theory of language acquisition was based on imitation, which is the notion that children learn to speak by imitating adults and older children. The difficulty with the imitation theory is that it fails to account for the ability of even small children to form new sentences from words they know. A second theory, associated with the behavioral school of psychology, maintains that language acquisition is explained by reinforcement. Children learn to speak because their parents give them positive reinforcement when they speak correctly and negative reinforcement (correction or criticism) when they speak ungrammatically. This theory does not hold up under the findings of recent research that parents reinforce the meaning of what children say rather than its grammatical correctness. In addition, children often chatter to themselves or to no one in particular for the sheer pleasure of talking. This activity is hard to explain in terms of the reinforcement theory.
A third theory of language acquisition is called nativism. This theory holds that humans are neurologically "programmed" from birth with the capacity to acquire language as soon as their nervous system reaches a certain point of maturation. Noam Chomsky maintained that the human brain has a built-in language acquisition device, or LAD, that analyzes the parts of speech in the language that a child hears. The phases of language acquisition and the age at which children begin to acquire language are similar enough across different cultures and different languages to give some support to the nativist view.
Biological and neuroanatomical features of language acquisition
EVOLUTION AND DEVELOPMENT OF THE HUMAN VOCAL TRACT AND NERVOUS SYSTEM. Language is, as far as we know, unique to humans. Chimpanzees are able to learn a rudimentary sign language, but they cannot combine vocalized sounds into meaningful structured combinations as humans do. The human mouth and throat appear to have been modified over the course of evolutionary history for speech. The human larynx is situated low in the throat, and the sharp right-angle bend at the back of the mouth divides the human vocal tract into two resonant cavities (the mouth and the throat) that allow for the production of a large range of vowel sounds.
The maturation of certain neural circuits in a child's brain may explain why language development proceeds most rapidly in young children after the first year of life. Although babies are born with most of their nerve cells already formed, their head size, brain weight, and junctions between nerve cells (synapses) continue to increase in the first year after birth. The long-distance connections in the child's nervous system are not complete until nine months of age, and the rate of metabolism in the child's brain reaches adult levels by ten months. There appears to be a neurologically determined critical period for language acquisition. Children acquire language easily until age four, or six at the latest. After puberty, it is rare for humans to learn to speak if they have not done so earlier.
AREAS OF THE BRAIN ASSOCIATED WITH LANGUAGE. The areas of the brain that govern the interpretation and production of language were discovered in the nineteenth century by physicians studying patients with speech disorders. In 1861, Pierre Paul Broca, a French physician, was able to demonstrate from post-mortems of patients who had lost the ability to speak, that the loss of this ability is associated with damage to an area of the brain toward the front of the left hemisphere. In 1876, a German physician named Karl Wernicke found that damage to an area in the posterior part of the left temporal lobe of the brain is also associated with language disorders. This area, now called Wernicke's area, is connected to Broca's area by a group of nerve fibers called the arcuate fasciculus.
When a person reads aloud, information from the eyes travels along the optic nerve to the primary visual cortex of the brain. From the primary visual cortex, the information is transmitted to Wernicke's area, where it is interpreted. From Wernicke's area, it is carried by the arcuate fasciculus to Broca's area, then to the primary motor cortex. When a person repeats a word that is spoken, the information is carried from the nerves in the ear to the primary auditory cortex in the brain. It is then transmitted from the primary auditory cortex to Wernicke's area, then to Broca's area via the arcuate fasciculus, then to the primary motor cortex.
Stages of language acquisition
A young human's acquisition of language takes place in a series of six stages:
Prelinguistic stage (birth to six months): The baby cries, coos, laughs, and makes other sounds.
Babbling (six to 12 months): The baby makes nonspecific sounds from all human languages.
One-word (holophrastic) stage (1–2 years): The child speaks single words in isolation, in his or her first language.
Two-word stage (24–30 months): The child forms two-word phrases or strings that reflect the language being acquired. The vocabulary increases; the child begins to learn words at the rate of one word every two waking hours.
Telegraphic speech (30–36 months): Children begin to utter short phrases like telegraph messages, without formal grammatical structure.
Fluent speech (three years +): The child learns grammar and syntax (patterns of sentence formation) with surprising rapidity and accuracy; sentences increase in length and complexity.
Function
Human language functions as a means of interpersonal communication, to convey thoughts, feelings, and many other forms of information. It is necessary to human social life as well as to intellectual development. Language also stimulates the expression of human creativity: poetry, drama, novels, short stories, vocal music, and similar forms of art are based on language.
Role in human health
The fact that language is unique to humans implies that language acquisition is necessary to full psychosocial as well as intellectual development. People who lose the ability to speak normally in later life because of a stroke or a condition known as primary progressive aphasia often become depressed because they feel cut off from others. Children and adolescents with dyslexia (a learning disability that affects reading and is sometimes related to problems understanding spoken language) often have additional difficulties learning to interact
with others and feeling comfortable in social situations.
Studies of "wild" children and children reared by emotionally disturbed parents who did not talk to them indicate that children who do not learn to speak by age eight never achieve normal fluency. This feature of language acquisition implies that language is an important component of the social dimension of human nature. Humans who have never acquired the ability to communicate with others cannot be completely socialized.
Aphasia
Aphasia refers to the loss of a previously held ability to speak or to understand written or spoken language. Aphasia is most often the result of a stroke or head trauma, but it can occur in relation to other neurological disorders. Primary progressive aphasia is a disorder of the nervous system in which the person's ability to speak gradually deteriorates. In Broca's aphasia, caused by damage to Broca's area, the person can understand what words mean, but has trouble with speech output. Broca's aphasia is sometimes called motor or expressive aphasia. In Wernicke's aphasia, caused by damage to Wernicke's area, the person cannot understand spoken language. They can speak, but their speech is ungrammatical and incoherent. Wernicke's aphasia is sometimes called fluent or receptive aphasia.
Dyslexia
Dyslexia is a disorder that affects the ability to read. Its symptoms may include problems with spelling, difficulty recognizing the sounds in words, problems processing visual information, and difficulty saying words quickly when asked to do so. Present dyslexia research is focused on studying the parts of the brain that process speech sounds and relate them to vision and other language areas in the brain.
Williams syndrome
Williams syndrome is a rare congenital disorder that occurs once in every 20,000 births. It results from a deletion of the genetic material on human chromosome 7 that makes a protein called elastin. Although children with Williams are usually mildly retarded, they often have normal language abilities. The dissociation of language acquisition from general intelligence in Williams syndrome suggests that human speech is not simply a byproduct of intelligence as such.
Specific language impairment (SLI)
Specific language impairment, or SLI, refers to a group of inherited syndromes in which children with normal intelligence and hearing are slow to acquire and use language. SLI is thought to affect 5–7% of children starting school. A cross-cultural study done in 1999 suggests that SLI may differ from other language disorders in that the number and specific types of problems the children had were related to their specific first language. The study showed that children learning Italian or Hebrew had fewer difficulties with verbs, for example, than children learning English.
KEY TERMS
Aphasia—The loss of previously held ability to speak or to understand written or spoken language, caused by disease or injury to the brain.
Arcuate fasciculus—A group of nerve fibers in the brain that connects Wernicke's area with Broca's area.
Broca's area—An area in the left hemisphere of the brain associated with the motor impulses necessary for speech. It is named for Pierre Paul Broca (1824-1880), a French physician.
Dyslexia—A reading disorder associated with impairment of the ability to integrate auditory and visual information, or to process sounds accurately.
Holophrastic—An early stage in language acquisition in which a single word serves the function of a phrase or sentence.
Nativism—The theory that humans have neural circuits that are genetically programmed to acquire language.
Wernicke's area—An area in the left hemisphere of the brain that is important in the reception and interpretation of speech. Wernicke's area is connected to Broca's area by the arcuate fasciculus.
Williams syndrome—A rare congenital disorder caused by a deletion of the elastin gene on chromosome 7. Children with Williams syndrome have normal language skills even though they are usually mildly retarded.
BOOKS
Fletcher, P., and B. MacWhinney. The Handbook of Child Language. Cambridge, MA: Blackwell Publishers, 1995.
Martin, John H., PhD. Neuroanatomy: Text and Atlas, second edition. Norwalk, CT: Appleton & Lange, 1996.
Pinker, Steven. The Language Instinct. New York: Morrow, 1994.
PERIODICALS
Toppelberg, Claudio O. "Several developmental disorders and bilingualism." Journal of the American Academy of Child and Adolescent Psychiatry 38, no. 9 (September, 1999).
ORGANIZATIONS
American Speech Language Hearing Association (ASHA). 10801 Rockville Pike, Rockville, MD 20852-3279. (301) 897-5700 or (800) 638-8255. Fax: (301) 571-0457. <http://www.asha.org>.
International Dyslexia Association. 8600 LaSalle Road, Chester Building, Suite 382, Baltimore, MD 21286-2044. (410) 296-0232. Fax: (410) 321-5069. <http://www.interdys.org>.
National Aphasia Foundation. 156 Fifth Avenue, Suite 707, New York, NY 10010. (800) 922-4622. <http://www.aphasia.org>.
National Institute of Child Health and Human Development (NICHD). National Institutes of Health, Bldg. 31, Room 2A32, Bethesda, MD 20892-2425. (301) 496-5133 or (800) 370-2943. <http://www.nichd.nih.gov>.
National Institute on Deafness and Other Communication Disorders (NIDCD). National Institutes of Health, Bldg. 31, Room 3C35, Bethesda, MD 20892-2320. (301) 496-7243. <http://www.nidcd.nih.gov>.
National Institute of Neurological Disorders and Stroke (NINDS). Building 31, Room 8A06, 9000 Rockville Pike, Bethesda, MD 20892. (301) 496-5751. <http://www.ninds.nih.gov>.
National Organization for Rare Disorders, Inc. (NORD) P. O. Box 8923, New Fairfield, CT 06812-8923. (203) 746-6518 or (800) 999-NORD. Fax: (203) 746-648. <http://www.rarediseases.org>.
Williams Syndrome Association. P.O. Box 297, Clawson, MI 48017-0297. (248) 541-3630. Fax: (248) 541-3631. <http://www.williams-syndrome.org>.
