Neurolinguistics
The neurolinguist addresses the fourth of our research questions: how is linguistic knowledge represented in the brain? It is easy to sympathise with the fundamental nature of this question, since we firmly believe that cognitive capa-cities are the product of structures in the brain. However, the direct study of the human brain is fraught with difficulties. Most obvious among these is the fact that ethical considerations forbid intrusive experimentation on human brains. Such considerations are not extended to non-humans, with the consequence that the neuroanatomy and neurophysiology of non-human, primate visual systems, similar in their capacities to that of humans, are already understood in some detail. For language, however, we have to rely on less controlled methods of investigation, for example, by studying brain-damaged patients who suffer from language disorders. In these circumstances, the extent and precise nature of the damage is not known, a factor which inevitably contributes to the tentativeness of conclusions.
The brain is an extremely complex organ, consisting of several ‘layers’. The layer which has evolved most recently and is most characteristic of higher primates such as ourselves is the cerebral cortex, the folded surface of the cerebral hemispheres, which contains what is often referred to as grey matter. This is where the higher intellectual functions, including language, are located. There are various ways in which the cerebral cortex can be damaged. For instance, it may suffer injury from a blow to the head or through some other type of wound. Alternatively, it may suffer internal damage due to disease or a blockage in a blood vessel (an embolism or thrombosis), which results in disruption of the blood supply and the death of cortical cells. Areas of damage are generally referred to as lesions.
The study of patients with various types of brain damage has revealed that different parts of the brain are associated with (i.e. control) different functions. In other words, it is possible to localise different functions in the brain as indicated in figure 1.
A language disorder resulting from brain damage is called aphasia, and a notable point is that this sort of brain damage almost always occurs in the left side of the brain (the left hemisphere). Damage to similar areas in the right hemisphere usually gives rise to entirely different deficits that have little to do with language. Aphasics who lose their language completely are said to suffer from global aphasia, and while in many cases the brain damage is extensive enough to affect other intellectual functions, sometimes patients retain a good many of the cognitive capacities they had before the injury. In particular, although these patients are unable to produce or understand language, they can often solve intellectual puzzles which don’t rely on language.
As we have seen, Chomsky claims that linguistic competence is the product of a species-specific innate language faculty, and it is further maintained that this faculty is independent of other cognitive capacities. Of course, the selective impairment of language with other faculties remaining intact, which we have just described, is exactly what we might expect on the supposition that the language faculty is an autonomous and innate cognitive capacity.
12 linguistics
Figure 1 The human cerebral cortex, with the functions of some areas indicated
Figure 2 The human cerebral cortex, with Broca’s Area (BA) and Wernicke’s Area (WA) indicated
As well as language being adversely affected while other aspects of cognitive functioning remain intact, it is possible for specific types of language function to be impaired, depending on where in the cortex the lesion occurs. In 1861 a French neurologist, Paul Broca, described a patient who had suffered a stroke and who could say only one word. After the patient’s death, Broca studied his brain and discovered a large lesion in the frontal lobe of the left hemisphere, the area BA in figure 2.
Broca concluded that this was the area of the brain responsible for controlling the production of speech, which has since come to be known as Broca’s area.
Introduction 13
Later research revealed that there is a second group of aphasic patients who have considerable difficulty in understanding language. In many cases, such
patients appear to produce language reasonably fluently, but close examination reveals that they often speak in a garbled fashion. This pattern of deficit is often referred to as Wernicke’s aphasia, in acknowledgement of Carl Wernicke, a German neurologist who first described it in detail in the 1870s. Wernicke’s aphasia is associated with damage to another area of the left hemisphere known as Wernicke’s area (WA in figure 2).
However, the initial view that language can be thought of as located in the left hemisphere and specifically in Broca’s and Wernicke’s areas has had to be refined. As more research has been done, it has become clear that several different areas of the brain are involved in performing linguistic tasks. This does not mean that the language faculty cannot be located in the brain, but it does entail that complex distributed representations are involved which require more sophisticated experi-mental procedures for their study. In recent years, new techniques have been developed for studying the activity of the brain as it performs a specific linguistic task. These so-called imaging techniques such as EEG (electroencephalography), MEG (magnetoencephalography) and fMRI (functional magnetic resonance imaging) provide images of the brain ‘at work’ and have led to a growth in our knowledge about the physiological mechanisms underlying the knowledge of language. Studies using these techniques have found, for example, that the brain areas dealing with grammar are not all in Broca’s area and that the areas involved in semantics are not all in Wernicke’s area. Instead, more recent brain-imaging research on language suggests that each of the different components of the language system (phonology, syntax, semantics, etc.) consists of subparts and these subparts are localised in different parts of the brain. Some of these are within the traditional language areas (Broca’s and Wernicke’s) and some outside, even in the right hemi-sphere. However, while we may hope that this research will ultimately lead to a brain map for language and language processing, it is still in a preliminary state, and in the relevant sections that follow (15 and 26), we shall restrict ourselves to
discussing the linguistic characteristics of patients who have suffered brain damage and who exhibit particular syndromes (exercise 7).
Of course, the brain is a biological organ, and above we have noted another aspect of the biological foundations of language: the claim that the language faculty is a product of human genetic endowment. Species-specificity is consistent with such a claim, but we might ask how we could obtain additional empirical evidence for it. One source of such evidence may be provided by the study of genetically caused disorders of language. If the availability of the language faculty (and the consequent ability to acquire a grammar) is indeed genetically controlled, then we would expect failures of this genetic control to result in language disorders. It is, therefore, of considerable interest that there is a group of language-impaired people who suffer from Specific Language Impairment
(SLI), a language disorder which must be clearly distinguished from the disorders introduced above, which are acquired as the result of damage to the brain. This
14 linguistics
group provides us with the chance of studying the effects of what is probably a genetically determined deficit in the acquisition of language. The specificity of SLI is indicated by the fact that SLI subjects have normal non-verbal IQs, no hearing deficits and no obvious emotional or behavioural difficulties. Its likely genetic source is suggested by the fact that it occurs in families, it is more frequent in boys than in girls and it affects both members of a pair of identical twins more frequently than it affects both members of a pair of fraternal twins. The nature of the impairment displayed by SLI subjects seems to be fairly narrow in scope, affecting aspects of grammatical inflection and certain complex syntactic pro-cesses. From this it might follow that if there is a ‘language gene’, its effects are rather specific and much of what is customarily regarded as language is not controlled by it. More research on SLI will be necessary before we can fully
evaluate its consequences for this issue, but we shall provide some additional discussion of these matters in sections 15 and 26 (exercise 8).
Up to now, we have focused on the four research questions raised by Chomsky’s programme and tried to give some idea of how we might begin to approach them. The idea of a grammar as a cognitive (ultimately, neurological)
structure is common to each of these fields, which also share an emphasis on the individual. At no point have we raised questions of language as a means of
communication with others, or as a tool for expressing membership in a group, or as indicative of geographical origins. These are intriguing issues and the sociolinguistic perspective addresses this omission.
Neurolinguistics
The neurolinguist addresses the fourth of our research questions: how is linguistic knowledge represented in the brain? It is easy to sympathise with the fundamental nature of this question, since we firmly believe that cognitive capa-cities are the product of structures in the brain. However, the direct study of the human brain is fraught with difficulties. Most obvious among these is the fact that ethical considerations forbid intrusive experimentation on human brains. Such considerations are not extended to non-humans, with the consequence that the neuroanatomy and neurophysiology of non-human, primate visual systems, similar in their capacities to that of humans, are already understood in some detail. For language, however, we have to rely on less controlled methods of investigation, for example, by studying brain-damaged patients who suffer from language disorders. In these circumstances, the extent and precise nature of the damage is not known, a factor which inevitably contributes to the tentativeness of conclusions.
The brain is an extremely complex organ, consisting of several ‘layers’. The layer which has evolved most recently and is most characteristic of higher primates such as ourselves is the cerebral cortex, the folded surface of the cerebral hemispheres, which contains what is often referred to as grey matter. This is where the higher intellectual functions, including language, are located. There are various ways in which the cerebral cortex can be damaged. For instance, it may suffer injury from a blow to the head or through some other type of wound. Alternatively, it may suffer internal damage due to disease or a blockage in a blood vessel (an embolism or thrombosis), which results in disruption of the blood supply and the death of cortical cells. Areas of damage are generally referred to as lesions.
The study of patients with various types of brain damage has revealed that different parts of the brain are associated with (i.e. control) different functions. In other words, it is possible to localise different functions in the brain as indicated in figure 1.
A language disorder resulting from brain damage is called aphasia, and a notable point is that this sort of brain damage almost always occurs in the left side of the brain (the left hemisphere). Damage to similar areas in the right hemisphere usually gives rise to entirely different deficits that have little to do with language. Aphasics who lose their language completely are said to suffer from global aphasia, and while in many cases the brain damage is extensive enough to affect other intellectual functions, sometimes patients retain a good many of the cognitive capacities they had before the injury. In particular, although these patients are unable to produce or understand language, they can often solve intellectual puzzles which don’t rely on language.
As we have seen, Chomsky claims that linguistic competence is the product of a species-specific innate language faculty, and it is further maintained that this faculty is independent of other cognitive capacities. Of course, the selective impairment of language with other faculties remaining intact, which we have just described, is exactly what we might expect on the supposition that the language faculty is an autonomous and innate cognitive capacity.
12 linguistics
Figure 1 The human cerebral cortex, with the functions of some areas indicated
Figure 2 The human cerebral cortex, with Broca’s Area (BA) and Wernicke’s Area (WA) indicated
As well as language being adversely affected while other aspects of cognitive functioning remain intact, it is possible for specific types of language function to be impaired, depending on where in the cortex the lesion occurs. In 1861 a French neurologist, Paul Broca, described a patient who had suffered a stroke and who could say only one word. After the patient’s death, Broca studied his brain and discovered a large lesion in the frontal lobe of the left hemisphere, the area BA in figure 2.
Broca concluded that this was the area of the brain responsible for controlling the production of speech, which has since come to be known as Broca’s area.
Introduction 13
Later research revealed that there is a second group of aphasic patients who have considerable difficulty in understanding language. In many cases, such
patients appear to produce language reasonably fluently, but close examination reveals that they often speak in a garbled fashion. This pattern of deficit is often referred to as Wernicke’s aphasia, in acknowledgement of Carl Wernicke, a German neurologist who first described it in detail in the 1870s. Wernicke’s aphasia is associated with damage to another area of the left hemisphere known as Wernicke’s area (WA in figure 2).
However, the initial view that language can be thought of as located in the left hemisphere and specifically in Broca’s and Wernicke’s areas has had to be refined. As more research has been done, it has become clear that several different areas of the brain are involved in performing linguistic tasks. This does not mean that the language faculty cannot be located in the brain, but it does entail that complex distributed representations are involved which require more sophisticated experi-mental procedures for their study. In recent years, new techniques have been developed for studying the activity of the brain as it performs a specific linguistic task. These so-called imaging techniques such as EEG (electroencephalography), MEG (magnetoencephalography) and fMRI (functional magnetic resonance imaging) provide images of the brain ‘at work’ and have led to a growth in our knowledge about the physiological mechanisms underlying the knowledge of language. Studies using these techniques have found, for example, that the brain areas dealing with grammar are not all in Broca’s area and that the areas involved in semantics are not all in Wernicke’s area. Instead, more recent brain-imaging research on language suggests that each of the different components of the language system (phonology, syntax, semantics, etc.) consists of subparts and these subparts are localised in different parts of the brain. Some of these are within the traditional language areas (Broca’s and Wernicke’s) and some outside, even in the right hemi-sphere. However, while we may hope that this research will ultimately lead to a brain map for language and language processing, it is still in a preliminary state, and in the relevant sections that follow (15 and 26), we shall restrict ourselves to
discussing the linguistic characteristics of patients who have suffered brain damage and who exhibit particular syndromes (exercise 7).
Of course, the brain is a biological organ, and above we have noted another aspect of the biological foundations of language: the claim that the language faculty is a product of human genetic endowment. Species-specificity is consistent with such a claim, but we might ask how we could obtain additional empirical evidence for it. One source of such evidence may be provided by the study of genetically caused disorders of language. If the availability of the language faculty (and the consequent ability to acquire a grammar) is indeed genetically controlled, then we would expect failures of this genetic control to result in language disorders. It is, therefore, of considerable interest that there is a group of language-impaired people who suffer from Specific Language Impairment
(SLI), a language disorder which must be clearly distinguished from the disorders introduced above, which are acquired as the result of damage to the brain. This
14 linguistics
group provides us with the chance of studying the effects of what is probably a genetically determined deficit in the acquisition of language. The specificity of SLI is indicated by the fact that SLI subjects have normal non-verbal IQs, no hearing deficits and no obvious emotional or behavioural difficulties. Its likely genetic source is suggested by the fact that it occurs in families, it is more frequent in boys than in girls and it affects both members of a pair of identical twins more frequently than it affects both members of a pair of fraternal twins. The nature of the impairment displayed by SLI subjects seems to be fairly narrow in scope, affecting aspects of grammatical inflection and certain complex syntactic pro-cesses. From this it might follow that if there is a ‘language gene’, its effects are rather specific and much of what is customarily regarded as language is not controlled by it. More research on SLI will be necessary before we can fully
evaluate its consequences for this issue, but we shall provide some additional discussion of these matters in sections 15 and 26 (exercise 8).
Up to now, we have focused on the four research questions raised by Chomsky’s programme and tried to give some idea of how we might begin to approach them. The idea of a grammar as a cognitive (ultimately, neurological)
structure is common to each of these fields, which also share an emphasis on the individual. At no point have we raised questions of language as a means of
communication with others, or as a tool for expressing membership in a group, or as indicative of geographical origins. These are intriguing issues and the sociolinguistic perspective addresses this omission.
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