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Essay: Aphasia and SLIs

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  • Published: 15 October 2019*
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  • Words: 1,286 (approx)
  • Number of pages: 6 (approx)
  • Tags: Child Development essays

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The study of linguistics, in particular language acquisition, is often hindered by phenomena that linguists have are yet to decipher. These hindrances include all manner of both environmental and experimental issues. It can be seen in the discipline of language acquisition that such a factor is individuals with varying forms of brain damage. Many learners of language with damage to either hemisphere of the brain can develop long lasting problems with speech and comprehension. I have been attracted to the topic due to both a personal interest in neurology and the sensitive nature of treating disorders such as aphasias and Specific Language Impairments (hereafter SLIs). Within the essay I will firstly explore the fundamental neuroscience that attempts to explain both aphasia and SLIs, after which I will review studies completed within the field to draw a metered conclusion on the effects of brain damage to language development.

Broca (1860) was among the first to discover that a particular region of the brain can be responsible for a type of aphasia; later known as “Broca’s area”. The patient he observed was almost entirely devoid of speech but his comprehension skills seemed to be intact. After his death an autopsy was carried out and it was discovered that there was severe damage to the front-left of the brain. Those who suffer aphasia in this region are said to have Broca’s aphasia which impairs the ability to speak but leaves comprehension skills intact. It can be observed that patients struggle with grammatical morphemes and gesticulation. Sufferers of Broca’s aphasia also produce telegraphic speech meaning that they lack crucial function words (Cook, 1997). Another form of aphasia that has been attributed to a specific area of the brain is Wernicke’s aphasia (Wernicke, 1874). It can be observed that patients of this form of aphasia are the antithesis of Broca’s aphasiacs. Wernicke’s aphasia sufferers have problems with pronunciation and comprehension but produce streams of consciousness that provide the illusion of fluency. Patients also take issue with naming things (known as anomia). Both Broca and Wernicke laid the foundations for research into how language is lateralised in the brain.

Lateralisation was theorised by Lenneberg (1967) when he hypothesised that both hemispheres of the brain are equipotential meaning that there is no cerebral asymmetry, at the same time presenting the notion of a critical period in language acquisition. Lenneberg also theorised that the brain lateralised through a process of maturation which usually occurs between 2-5 years and is completely finished by puberty. This period of maturation is more often referred to as the critical period. Later, Krashen (1973) observed that the end of this maturation/lateralisation process is much earlier, placing it at five years. Furthermore, Entus (1977) produced evidence that there is in fact lateralisation at an early age through sucking habituation experiments showing that children as young as one week seem to prefer the left hemisphere for speech. As medical technology has developed, researchers have been able to look at the brain in more detail using computerised tomography scanning (CT), positron emission tomography (PET) and functional magnetic resonance imaging (fMRI). An experiment measuring event related potentials (ERPs) in the brains of children between 13 and 20 months showed that between 13 and 17 months, language activity is spread across both hemispheres of the brain, localising by 20 months in the centre of the left hemisphere (Mills et al, 1993). This suggests that Lenneberg’s original theory of lateralisation is flawed and that the ages he proposed to be the boundaries of maturation may be overestimated. There are other areas of the brain responsible for various language function as well as Wernicke’s and Broca’s area such as Heschl’s gyri (Heschl, 1878), said to be the area of the brain responsible for auditory reception. As Broca and Wernicke laid foundations for the research into how language can be approached in respect to the mind, the aforementioned studies lay foundations for research into hemispheric brain damage and damage to certain areas of the brain. It can be observed that damage to different areas of the brain (Broca’s and Wernicke’s areas being pivotal here) cause long-lasting, often permanent effects on language production and comprehension. In particular, damage to the left hemisphere in adults leads to severe language impairment (Harley, 2014). Mirroring this, language development in children with early hemisphere damage is shown to be stunted. It has been observed that children with left hemisphere damage have delays in lexical production, worsening as time progresses. Damage to the right hemisphere often causes no problems with language in adults but it can be observed in children that they have long-lasting problems with language. It can be observed that patients that have undergone hemidecortication of the left hemisphere lose all language ability, however, patients may regain minimal language ability suggesting that some language capability is in the right hemisphere (Kinsbourne, 1975). Furthermore, it appears that the right hemisphere has a part to play in language comprehension as those with damage to the right hemisphere often lose the ability to understand intonation, jokes and metaphor (Caplan, 1987). Echoing this, it can be seen in the development of children with right hemisphere damage that their comprehension abilities are lacking.

In children with early injury to the brain there can be delays in gestural development (Sauer et al 2010). Interestingly, it has been observed that children with early hemisphere damage appear to have the same phonological development as those without lesions (Marchman et al, 1991). Reports have consistently shown that children with autism have trouble acquiring their first words, phrases and sentences (Charman et al, 2003; Grandgeorge et al, 2009; Anderson et al, 2007). Fulton & D’Entrement (2013) also showed that autistic children have trouble with relations, morphemes and intonation compared to their peers. An SLI can be described as “a condition in which a child who appears otherwise normal fails to acquire language like its peers” (Field, 2004). Conditions such as autism, Down’s syndrome, schizophrenia and William’s syndrome are not to be classed as SLIs due to language impairment being associated with other developmental issues. SLI is said to effect ~7% of American English speaking children (Tomblin, Smith & Zhang, 1997). A study by Gopnik (1990) theorised that three generations of the same family were affected by an SLI, suggesting a hereditary condition. Interestingly, this study highlighted that whilst those tested performed well in “general grammaticality judgement tasks” (Field, 2004), their speech and language lacked crucial inflectional features such as gender, number and plurals, showing that SLI does not correlate with general intelligence.

In conclusion it can be seen that damage to either hemisphere of the brain can cause an abrupt stunt to the language development of a child. In particular, damage to the left hemisphere produces considerable loss of speech production supporting the notion that language is left lateralised. It can also be seen that children with left hemisphere damage develop problems with gesture and struggle with morphemes and inflection. Children suffering right hemisphere damage have problems with syntactic comprehension but for the most part have language ability intact. From this we can draw that language acquisition does indeed appear to involve a process of lateralisation and maturation as Lenneberg hypothesised. The process of lateralisation is crucial to understand language development as it appears that certain aspects of both spoken and written language settle in both hemispheres, with comprehension falling into the right hemisphere and phonetic production falling into the left, broadly speaking. In terms of SLI, Gopnik shows us that language impairment may be hereditary. His work also highlights that SLI does not necessarily inhibit intelligence. Furthermore, studies of autism show that production of first words and phrases are delayed, alike sufferers of left hemisphere brain damage. Overall, it can be seen that language development is affected by brain damage in the context

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