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In aphasia, a person may be unable to comprehend or unable to formulate language because of damage to specific brain regions. The major causes are stroke and head trauma; prevalence is hard to determine but aphasia due to stroke is estimated to be 0.1–0.4% in the Global North. Aphasia can also be the result of brain tumors, epilepsy, autoimmune neurological diseases, brain infections, or neurodegenerative diseases.
Expressive aphasia, also known as Broca's aphasia, is a type of aphasia characterized by partial loss of the ability to produce language, although comprehension generally remains intact. A person with expressive aphasia will exhibit effortful speech. Speech generally includes important content words but leaves out function words that have more grammatical significance than physical meaning, such as prepositions and articles. This is known as "telegraphic speech". The person's intended message may still be understood, but their sentence will not be grammatically correct. In very severe forms of expressive aphasia, a person may only speak using single word utterances. Typically, comprehension is mildly to moderately impaired in expressive aphasia due to difficulty understanding complex grammar.
In neuroscience and psychology, the term language center refers collectively to the areas of the brain which serve a particular function for speech processing and production. Language is a core system that gives humans the capacity to solve difficult problems and provides them with a unique type of social interaction. Language allows individuals to attribute symbols to specific concepts, and utilize them through sentences and phrases that follow proper grammatical rules. Finally, speech is the mechanism by which language is orally expressed.
Wernicke's aphasia, also known as receptive aphasia, sensory aphasia or posterior aphasia, is a type of aphasia in which individuals have difficulty understanding written and spoken language. Patients with Wernicke's aphasia demonstrate fluent speech, which is characterized by typical speech rate, intact syntactic abilities and effortless speech output. Writing often reflects speech in that it tends to lack content or meaning. In most cases, motor deficits do not occur in individuals with Wernicke's aphasia. Therefore, they may produce a large amount of speech without much meaning. Individuals with Wernicke's aphasia are typically unaware of their errors in speech and do not realize their speech may lack meaning. They typically remain unaware of even their most profound language deficits.
Neurolinguistics is the study of neural mechanisms in the human brain that control the comprehension, production, and acquisition of language. As an interdisciplinary field, neurolinguistics draws methods and theories from fields such as neuroscience, linguistics, cognitive science, communication disorders and neuropsychology. Researchers are drawn to the field from a variety of backgrounds, bringing along a variety of experimental techniques as well as widely varying theoretical perspectives. Much work in neurolinguistics is informed by models in psycholinguistics and theoretical linguistics, and is focused on investigating how the brain can implement the processes that theoretical and psycholinguistics propose are necessary in producing and comprehending language. Neurolinguists study the physiological mechanisms by which the brain processes information related to language, and evaluate linguistic and psycholinguistic theories, using aphasiology, brain imaging, electrophysiology, and computer modeling.
Aphasiology is the study of language impairment usually resulting from brain damage, due to neurovascular accident—hemorrhage, stroke—or associated with a variety of neurodegenerative diseases, including different types of dementia. These specific language deficits, termed aphasias, may be defined as impairments of language production or comprehension that cannot be attributed to trivial causes such as deafness or oral paralysis. A number of aphasias have been described, but two are best known: expressive aphasia and receptive aphasia.
Anomic aphasia is a mild, fluent type of aphasia where individuals have word retrieval failures and cannot express the words they want to say. By contrast, anomia is a deficit of expressive language, and a symptom of all forms of aphasia, but patients whose primary deficit is word retrieval are diagnosed with anomic aphasia. Individuals with aphasia who display anomia can often describe an object in detail and maybe even use hand gestures to demonstrate how the object is used, but cannot find the appropriate word to name the object. Patients with anomic aphasia have relatively preserved speech fluency, repetition, comprehension, and grammatical speech.
Wernicke's area, also called Wernicke's speech area, is one of the two parts of the cerebral cortex that are linked to speech, the other being Broca's area. It is involved in the comprehension of written and spoken language, in contrast to Broca's area, which is primarily involved in the production of language. It is traditionally thought to reside in Brodmann area 22, which is located in the superior temporal gyrus in the dominant cerebral hemisphere, which is the left hemisphere in about 95% of right-handed individuals and 70% of left-handed individuals.
A word salad is a "confused or unintelligible mixture of seemingly random words and phrases", most often used to describe a symptom of a neurological or mental disorder. The name schizophasia is used in particular to describe the confused language that may be evident in schizophrenia. The words may or may not be grammatically correct, but they are semantically confused to the point that the listener cannot extract any meaning from them. The term is often used in psychiatry as well as in theoretical linguistics to describe a type of grammatical acceptability judgement by native speakers, and in computer programming to describe textual randomization.
Conduction aphasia, also called associative aphasia, is an uncommon form of difficulty in speaking (aphasia). It is caused by damage to the parietal lobe of the brain. An acquired language disorder, it is characterised by intact auditory comprehension, coherent speech production, but poor speech repetition. Affected people are fully capable of understanding what they are hearing, but fail to encode phonological information for production. This deficit is load-sensitive as the person shows significant difficulty repeating phrases, particularly as the phrases increase in length and complexity and as they stumble over words they are attempting to pronounce. People have frequent errors during spontaneous speech, such as substituting or transposing sounds. They are also aware of their errors and will show significant difficulty correcting them.
Transcortical sensory aphasia (TSA) is a kind of aphasia that involves damage to specific areas of the temporal lobe of the brain, resulting in symptoms such as poor auditory comprehension, relatively intact repetition, and fluent speech with semantic paraphasias present. TSA is a fluent aphasia similar to Wernicke's aphasia, with the exception of a strong ability to repeat words and phrases. The person may repeat questions rather than answer them ("echolalia").
Transcortical motor aphasia (TMoA), also known as commissural dysphasia or white matter dysphasia, results from damage in the anterior superior frontal lobe of the language-dominant hemisphere. This damage is typically due to cerebrovascular accident (CVA). TMoA is generally characterized by reduced speech output, which is a result of dysfunction of the affected region of the brain. The left hemisphere is usually responsible for performing language functions, although left-handed individuals have been shown to perform language functions using either their left or right hemisphere depending on the individual. The anterior frontal lobes of the language-dominant hemisphere are essential for initiating and maintaining speech. Because of this, individuals with TMoA often present with difficulty in speech maintenance and initiation.
Progressive nonfluent aphasia (PNFA) is one of three clinical syndromes associated with frontotemporal lobar degeneration. PNFA has an insidious onset of language deficits over time as opposed to other stroke-based aphasias, which occur acutely following trauma to the brain. The specific degeneration of the frontal and temporal lobes in PNFA creates hallmark language deficits differentiating this disorder from other Alzheimer-type disorders by the initial absence of other cognitive and memory deficits. This disorder commonly has a primary effect on the left hemisphere, causing the symptomatic display of expressive language deficits and sometimes may disrupt receptive abilities in comprehending grammatically complex language.
Primary progressive aphasia (PPA) is a type of neurological syndrome in which language capabilities slowly and progressively become impaired. As with other types of aphasia, the symptoms that accompany PPA depend on what parts of the left hemisphere are significantly damaged. However, unlike most other aphasias, PPA results from continuous deterioration in brain tissue, which leads to early symptoms being far less detrimental than later symptoms.
A speech error, commonly referred to as a slip of the tongue or misspeaking, is a deviation from the apparently intended form of an utterance. They can be subdivided into spontaneously and inadvertently produced speech errors and intentionally produced word-plays or puns. Another distinction can be drawn between production and comprehension errors. Errors in speech production and perception are also called performance errors. Some examples of speech error include sound exchange or sound anticipation errors. In sound exchange errors, the order of two individual morphemes is reversed, while in sound anticipation errors a sound from a later syllable replaces one from an earlier syllable. Slips of the tongue are a normal and common occurrence. One study shows that most people can make up to as much as 22 slips of the tongue per day.
Agrammatism is a characteristic of non-fluent aphasia. Individuals with agrammatism present with speech that is characterized by containing mainly content words, with a lack of function words. For example, when asked to describe a picture of children playing in the park, the affected individual responds with, "trees..children..run." People with agrammatism may have telegraphic speech, a unique speech pattern with simplified formation of sentences, akin to that found in telegraph messages. Deficits in agrammaticism are often language-specific, however—in other words, "agrammaticism" in speakers of one language may present differently from in speakers of another.
The term linguistic performance was used by Noam Chomsky in 1960 to describe "the actual use of language in concrete situations". It is used to describe both the production, sometimes called parole, as well as the comprehension of language. Performance is defined in opposition to "competence"; the latter describes the mental knowledge that a speaker or listener has of language.
Paraphasia is a type of language output error commonly associated with aphasia, and characterized by the production of unintended syllables, words, or phrases during the effort to speak. Paraphasic errors are most common in patients with fluent forms of aphasia, and come in three forms: phonemic or literal, neologistic, and verbal. Paraphasias can affect metrical information, segmental information, number of syllables, or both. Some paraphasias preserve the meter without segmentation, and some do the opposite. However, most paraphasias affect both partially.
Jargon aphasia is a type of fluent aphasia in which an individual's speech is incomprehensible, but appears to make sense to the individual. Persons experiencing this condition will either replace a desired word with another that sounds or looks like the original one, or has some other connection to it, or they will replace it with random sounds. Accordingly, persons with jargon aphasia often use neologisms, and may perseverate if they try to replace the words they can not find with sounds.
Sign language refers to any natural language which uses visual gestures produced by the hands and body language to express meaning. The brain's left side is the dominant side utilized for producing and understanding sign language, just as it is for speech. In 1861, Paul Broca studied patients with the ability to understand spoken languages but the inability to produce them. The damaged area was named Broca's area, and located in the left hemisphere’s inferior frontal gyrus. Soon after, in 1874, Carl Wernicke studied patients with the reverse deficits: patients could produce spoken language, but could not comprehend it. The damaged area was named Wernicke's area, and is located in the left hemisphere’s posterior superior temporal gyrus.
References
- ↑ "Definition of paragrammatism". Oxford Dictionaries (British & World English). Archived from the original on October 10, 2012.
- 1 2 Butterworth, Brian; Howard, David (1987). "Paragrammatisms". Cognition. 26 (1): 1–37. doi:10.1016/0010-0277(87)90012-6. ISSN 0010-0277. PMID 3608394. S2CID 235331431.
- ↑ Heeschen, Claus; Kolk, Herman (1988). "Agrammatism and paragrammatism". Aphasiology. 2 (3–4): 299–302. doi:10.1080/02687038808248928. ISSN 0268-7038.
- ↑ "Understanding paragrammatism: A comparative case study". Aphasiology (2008). 2008.