Neurolinguistics: The Study of Language and the Brain - Broca's and Wernicke's Areas - Pro, Apuntes de Lingüística

¡Descarga Neurolinguistics: The Study of Language and the Brain - Broca's and Wernicke's Areas - Pro y más Apuntes en PDF de Lingüística solo en Docsity! CHAPTER 12 LANGUAGE AND THE BRAIN The study of the relationship between language and the brain is called neurolinguistics. The field of study dates back to the nineteenth century. Since that time, a number of discoveries have been made about the specific parts in the brain that are related to language functions. We know that the most important parts are in areas around the left ear. The shaded areas in this illustration indicate the general locations of those language functions involved in speaking and listening. We have come to know that these areas exist largely through the examination, in autopsies of the brains of people who, in life, were known to have specific language disabilities. We have tried to determine where language abilities for normal users must be by finding areas with specific damage in the brains of people who had identifiable language disabilities. BROCA’S AREA Paul Broca reported in 1860 that damage to this specific part of the brain was related to extreme difficulty in producing spoken language. It was noted that damage to the corresponding area on the right hemisphere had no such effect. This finding was first used to argue that language ability must be located in the left hemisphere and since then has been treated as an indication that Broca’s area is crucially involved in the generation of spoken language. WERNICKE’S AREA Carl Wernicke reported in 1870 that damage to this part of the brain was found among patients who had speech comprehension difficulties. This finding confirmed the left hemisphere location of language ability and led to the view that Wernicke’s area is part of the brain crucially involved in the understanding of speech. THE MOTOR CORTEX AND THE ARCUATE FASCICULUS The motor cortex is an area that generally controls movement of the muscles. Close to Broca’s area is the part of the motor cortex that controls the articulatory muscles of the face, jaw, tongue and larynx. Evidence that this area is involved in the physical articulation of speech comes from work reporter in the 1950s by two neurosurgeons. These researchers found that, by applying small amounts of electrical current to specific areas of the brain, they could identify those areas where the electrical stimulation would interfere with normal speech production. The arcuate fasciculus is known to form a crucial connection between Wernicke’s and Broca’s areas. THE LOCALIZATION VIEW Having identified these four components, it is tempting to conclude that specific aspects of language ability can be accorded specific locations in the brain. This is called the localization view and it has been used to suggest that the brain activity involved in hearing a word, understanding it, then saying it, would follow a definite pattern. The word is heard and comprehended via Wernicke’s area. This signal is then transferred via the arcuate fasciculus to Broca’s area where preparations are made to generate a spoken version of the word. A signal is then sent to part of the motor cortex to physically articulate the word. This is certainly an oversimplified version of what may actually take place, but it is consistent with much of what we understand about simple language processing in the brain. It is probably best to think of any proposal concerning processing pathways in the brain as some form of metaphor that may turn out to be inadequate once we learn more about how the brain functions. The ‘’pathway’’ metaphor seems quite appealing in an electronic age when we are familiar with the process of sending signals through electrical circuits. Sigmund Freud employed a ‘’steam engine’’ metaphor to account for aspects of the brain’s activity when he wrote of the effects of repression ‘’building up pressure’’ to the point of ‘’sudden release’’. We are forced to use metaphors mainly because we cannot obtain direct physical evidence of linguistic processes in the brain. Because we have no direct access, we generally have to rely on what we can discover through indirect methods. Most of these WERNICKE’S APHASIA The type of language disorder that results in difficulties in auditory comprehension is sometimes called ‘’sensory aphasia’’ but is more commonly known as Wernicke’s aphasia. Someone suffering from this disorder can actually produce very fluent speech which is often difficult to make sense of. Very general terms are used, even in response to specific requests for information, as in this sample: I can’t talk all of the things I do, and part of the part I can go alright, but I can´t tell from the other people. Difficulty in findings the correct word, sometimes referred to as anomia, also happens in Wernicke’s aphasia. Speakers use different strategies such as trying to describe objects or talking about their purpose, as in the thing to put cigarettes in (for ashtray). The speaker tries a range of strategies when he can’t come up with the word. CONDUCTION APHASIA This type of aphasia has been associated with damage to the arcuate fasciculus, it is much less common, and it is called conduction aphasia. Individuals suffering from this disorder sometimes mispronounce words, but typically do not have articulation problems. They are fluent, but may have disrupted rhythm because of the pauses and hesitations. Comprehension of spoken words is normally good. The task of repeating a word or phrase creates major difficulty, with forms such as vaysse and fosh being reported as attempted repetitions of the words forms such as ‘’base’’ and ‘’wash’’. What the speaker hears and understands can’t be transferred very successfully to the speech production area. It should be emphasized that many of these symptoms can occur in all types of aphasia. They can also occur in more general disorders resulting from brain disease, as in dementia and Alzheimer’s disease. Difficulties in speaking can also be accompanied by difficulties in writing. Language disorders of the type we have described are almost always the result of injury to the left hemisphere. This left hemisphere dominance for language has also been demonstrated by another approach to the investigation of language and the brain. DICHOTIC LISTENING An experimental technique that has demonstrated a left hemisphere dominance for syllable and word processing is called the dichotic listening test. This technique uses the generally stablished fact that anything experienced on the right-hand side of the body is processed in the left hemisphere, and anything on the left side is processed in the right hemisphere. A basic assumption would be that a signal coming in the right ear will go to the left hemisphere and a signal coming in the left ear will go to the right hemisphere. LEFT BRAIN, RIGHT BRAIN In this process, the language signal received through the left ear is first sent to the right hemisphere and then has to be sent to the left hemisphere (language center) for processing. This non-direct route takes longer than a linguistic signal received through the right ear, which goes directly to the left hemisphere. First signal to get processed wins because of what is generally known as the right ear advantage for speech sounds. The right hemisphere appears to have primary responsibility for processing a lot of other incoming signals that are non-linguistic. In the dichotic listening test, it can be shown that non-verbal sounds are recognized more often via the left ear, meaning they are processed faster via the right hemisphere. So, among the specializations of the human brain, the right hemisphere is first choice for non-language sounds and the left hemisphere specializes in language sounds. These specializations may actually have more to do with the type of processing rather than the type of material that is handled best by each of the two hemispheres. The essential distinction seems to be between analytic processing, such as recognizing the smaller details of sounds, words and phrase structures in rapid sequence, done with the left brain, and holistic processing such as identifying more general structures in language and experience, done with the right brain. THE CRITICAL PERIOD The apparent specialization of the left hemisphere for language is usually described in terms of lateral dominance or lateralization. Since the human child does not emerge from the womb as a fully articulate language-user, it is generally thought that the lateralization process begins in early childhood. It coincides with the period during which language acquisition takes place. During childhood, there is a period when the human brain is most ready to receive input and learn a particular language, this is sometimes called the ‘’sensitive period’’ for language acquisition, but is more generally known as the critical period. From birth until puberty, if a child does not acquire language, for any one of a number of reasons, then he or she will find it almost impossible to learn language later on.