How is language viewed from neuropsychology perspective? - Chapter 9

Why is knowledge of language important?

Every year a lot of cerebrovascular accidents (CVAs) occur, and around 20% of these cases involve language or speech impairments. Since CVAs are very common at later ages, the prevalence will increase in the future.

What does communication consist of?

After speech, writing is the most used medium to transfer messages to other human beings in order to communicate. According to Crystal (1992) language is systematic (bound by rules), conventional (based on agreements) and symbolic (words refer to an arbitrary concept). Language does not necessarily have to be communicative (this could include self-expression, such as the writing of a poem or the singing of a song). The characteristic that primarily makes human language unique is that it uses limited resources. Words can be combined over and over again in new ways in grammatically organised sequences.

What is the cognition of language?

Language is a cognitive system. The system starts producing language by a pre-verbal message and ends with an acoustic or graphic form. A message must also be understood. A form is observed, which ends in a mental representation.

The mental lexicon

The mental lexicon is similar to a mental dictionary and is part of the semantic memory system. Not only single words but also sentences and expressions that we use frequently are stored as a whole in our lexicon. There are three types of information available for each saved word: attributes related to meaning (the concept), grammatical attributes, and characteristics relating to form. The attributes relating to meaning are organized on the basis of characteristic agreements ("cat" is linked to the concept of "dog" but also to the concept of "cat food"). The information about grammatical attributes has to be stored in the lexicon as one of the grammatical characteristics of a word. The representation of the grammatical characteristics of a word is often called a 'lemma'. The characteristics relating to form are represented in the lexicon by abstract units of sound that are called 'phonemes'.

How is language processed?

The sound waves that are caused by speech vary in amplitude (the loudness) and the speed or frequency (the pitch). Phonemes can be identified based on these differences. The mental lexicon then searches for a word (series of phonemes) that matches the word just heard. All words that partly match the word are activated (with the word "''inquiry" the words "ink, choir, inquire, inquiry, why, wire, and wiry" become active). These words compete with the target word to be recognized and are called candidate words. As soon as word recognition takes place (the target word has won) the grammatical and meaning characteristics become available. The language system then determines the meaning of a sentence by looking at how each word relates to preceding and following words: this process is called "parsing."

How is language produced?

According to Levelt's language production system (1989), the "conceptualiser" is the mechanism responsible for choosing a message to communicate. This message is then only an abstract idea, but it does contain enough information to activate words in the lexicon. The “formulator” casts the message in a grammatical form: the grammatical coding takes place. To quote the book: this series is 'dressed' with sound information: the phonological coding. This phonetic plan (inner speech) travels to the next level: the "articulator" where the articulation organs (the larynx, the tongue, the lower jaw and the lips) convert the plan into sound. The "monitor" monitors whether the message is spoken loud enough, whether the utterance is grammatically correct, whether the speech is loud enough, and so on. 

What kinds of language impairments can be distinguished?

Aphasia

An aphasia is a collective term for acquired language impairments, which are usually expressed in all modalities. Aphasia is commonly caused by a stroke; less often the cause is found in traumatic brain injury or a brain tumor. The result is a focal, localised trauma.

Impairments known within language production

People with aphasia have impairments in language production, including major word problems. As a result, they omit words (omissions) or replace the word they are looking for with another word (replacement). Substitutions (paraphasias) can be expressed in various forms:

• A lexical paraphasia: the target word is replaced by an existing word which is usually (but not always) related to the target word (chosen from the same semantic network).

• A phonological paraphasia: at least one sound of the target word is omitted or replaced by another sound which often results in a non-existing word. A 'neologism' is a word of which it is unclear what it represents, because of the large amount of replaced or omitted sounds. If a patient uses a lot of neologism, he / she speaks in 'jargon'.

Sometimes the aphasia is so serious that meaningful speech is no longer present. The patient then switches to a form of 'non-propositional speech':

• 'Stereotype': the patient frequently uses expressions that have little meaning and are irrelevant to the communication, such as "I don't know" or "how do you say that?" with a lack of other meaningful sentences.

• 'Recurring utterances': the patient produces one or more utterances (sounds, words, or sentences) in all kinds of inappropriate situations (using the phrase 'Marks and Spencer' for everything). 

• 'Serial speech': the patient can still finish common, well-memorised strings (speech therapist: “1..2..3..4..5..6 ..”, patient: “..7..8. .9 ... 10 ")

• Echolalia: the patient repeats what their conversation partner says. This can consist of entire sentences or, for example, the last word. 

• Perseveration: the patient involuntarily repeats words or phrases.

Forms of syntax

There are two forms of syntax problems that often occur with aphasia patients:

1. Agrammatism: patients have difficulty using the grammatical knowledge correctly. The grammar repertoire is therefore very limited and patients only use short, easy sentences (telegram style). Example: Girl ... walk... home.

2. Paragrammatism: the sentences are long and complex. The sentences are very difficult to understand because of the large number of paraphasias as well as the incorrect use of conjugations, declensions, and function words. Example: Yes it is the language you know it stays where it is when I when you talk to me then I need sometimes one hour need I to say what I would like to say that's non nonsense. 

Which impairments are known in language comprehension?

Some aphasia patients have difficulty distinguishing phonemes: if they have to point to a pea, and that picture shows both a bee and a pea, then they have difficulty choosing between them. Problems can arise not only at the sound and word level, but also at sentence level. Especially when it cannot be deduced from the independent words of the sentence who does what, the sentences are difficult to understand. Example from the book: "The boy is kissed by the girl": the words "boy", "girl" and "kiss" do not indicate who is being kissed. Such sentences are 'reversible passives' where patients with aphasia have to guess the meaning ('agrammatical comprehension'). With a sentence like "The girl pours the tea" it is clear that the tea is poured by the girl: there is only one common meaning.

How can aphasia be classified?

The taxonomy influenced by Broca, Wernicke and Lichtheim - 'classical aphasiology' is the most widely used taxonomy of aphasia.

• Broca's aphasia: the language concept is intact. Patients have a lot of trouble with articulation and finding the right words, so the speech rate is very low. Often the patients are agrammatic. They have difficulty repeating.

• Wernicke's aphasia: speech is fluent, but the language concept is strongly affected. There are many phonological and semantic paraphasias and often there is paragrammatism. There is little insight into the disease here. The patient talks a lot but says little. Here too repeating is affected.

• Conduction aphasia: the language concept is fairly intact and the language production is similar to that of Wernicke's aphasia. The biggest problem in this case is repeating spoken words. Patients do have disease insight because they are trying to correct their mistakes. This helps: a phenomenon called "conduite d'approche".

• Transcortical aphasia: in sensory transcortical aphasia there are problems in language comprehension (as with Wernicke), and production, but repeating is intact. In motor transcortical aphasia, the patient experiences problems in language production (such as with Broca), not in language comprehension and repetition is also intact.

• Global aphasia: both production and comprehension are affected. 

• Amnestic aphasia: language production and language comprehension are intact (no agrammatism, paragrammatism, or paraphasias). However, there is a very serious problem in finding the right words. This mainly concerns nouns, while in other forms of aphasia the problem of finding words is mainly the verbs.

Only 25% of all aphasia patients have a pure aphasia syndrome: most have a mixed form.

The PALPA model

The descriptions of the symptoms of aphasia patients from Ellis and Young (1988) formed the basis of the PALPA model (a test battery). The PALPA model distinguishes many highly specialized processing modules. Each module can be lost after damage. A careful inventory can be used to determine precisely which module is affected in the language processing system. This model recognizes the complexity of the language system. This model is mainly theoretical because a neural substrate has not yet been identified for each component.

What are speech impairments?

'Dyspraxia' and 'dysarthria' are speech disorders that often coexist with aphasia. With a verbal dyspraxia something goes wrong in the programming of the articulation organs. The language system is intact and the articulation organs are also intact, but the articulatory movements are imprecise and uncoordinated. Longer words are much harder to pronounce than shorter words. Sequences of sounds are also major challenges. Dysarthria is a generic name for speech impairments that are caused by a lack of control over the articulation muscles as a result of damage to the motor part of the central nervous system or the peripheral nervous system. Muscle impairment itself may also be a cause of dysarthria. Different types of dysarthria are known, and in each type, damage in located in another brain area. 

What kinds of reading impairments do exist?

Aphasia patients often have acquired dyslexia: a collective name for some specific types of reading disorders. The following types are common:

• Attention dyslexia: the patient cannot name the individual letters.

• Neglect dyslexia / positional dyslexia: the patient reads the letters of one half of the word incorrectly, causing him / her to make many mistakes when reading.

• Semantic dyslexia / deep dyslexia: the patient does not read the written word, but a word that is semantically related to that word.

• Phonological dyslexia: the patient can read existing words, but cannot read pseudo words (non-existent words).

• Surface or surface dyslexia: the patient can read all words, but regularly spelled words are much better read than irregularly spelled words.

Which writing disorders are there?

Writing problems that occur in aphasia patients are the following:

• Phonological dysgraphia: pseudo words cannot be written down.

• Surface dysgraphia: regularly spelled words are better written than irregularly spelled words.

• Graphemic buffer dysgraphia: the word form is intact but the letters are replaced by other (incorrect) letters or the order of letters is reversed

What are new insights in the neurocognition of language?

Damage in frontal areas causes disrupted speech production (Broca's aphasia) because the articulatory patterns of words are located in this area, near the areas that control the tongue and mouth. Damage in posterior parts of the brain disrupts the concept of language (Wernicke's aphasia) because the sound images of words are stored in the posterior areas around the auditory processing area. This model, elaborated by Wernicke, was later expanded by Lichtheim (1885). Contemporary insights reveal that the Wernicke-Lichtheim schema is very simplified because it is assumed that there is a one-to-one relationship between disorder and tissue damage. Three nuances that must be applied are therefore the following:

• Broca's territory is not specifically linked to language production, just like Wernicke's territory is not specifically linked to language comprehension.

• There is indeed involvement of the right hemisphere.

• The 'language centers' are also involved in other processes.