Damage To Language Areas

Aphasia

Strokes are caused by cerebrovascular accidents.

Aphasia affects all language modalities/functions (reading, writing, speaking, etc). All abnormalities tell us about normality, by looking at the causes, and it is a result of these aphasic studies that language was the first cognitive function to be localised in the brain.

Aphasia can be split into two forms; fluent vs non-fluent.

Non-Fluent

Speech is slow, stilted and interrupted. This is also called motor aphasia.

Broca's Aphasia

Broca's Aphasia is type 1 non-fluent. It results from damage to the third convolution of the frontal lobe, in front of the central sulcus (Broca's area).

Speech Type

Broca's aphasics speak slowly, haltingly and laboriously and often drop off inflections and difficult phonemes (-ing/-est/a/an/'s/etc). They speak with dysprosody (their utterances lack normal sentence intonation - thought to be partially caused by the separation of the words).
Similarly to children acquiring language, Broca's aphasics show syllable reduction and clustering (spoon -> poon, with -> wit), and use telegraphic speech (a sign of a deeper syntactic disturbance, rather than for the sake of physical effort economy (given the lack of motor control impairment).

Motor Control of Speech

The bottom reach portion of motor control is in the front lobe, and hence speech motor control is thought to be affected. However there are two reasons not to believe this is the full story:

  1. Patients can perform all the necessary facial muscle activities (they can suck and blow) - they merely have a mild weakness to the right side of the facial muscles.
  2. Sufferers tend to write the way they speak (it affects all modalities)

Comprehension

Broca's aphasics are often not up to the task of providing grammaticality judgements, and it generally has to be speech pathologists who are working with the patients who elicit information about their language competence. We do know that they tend to be able to fully understand what people are saying to them, but have difficulty comprehending passive/complex syntax.

For instance, aphasics can get the content out of "the boy ate it up" without understanding much of the syntax. They deal by using strategies like world knowledge for context, and controlling conversation topics to shortcut comprehension.

The job of a psycholinguist is to discover ways of getting past the facades and tricks.

Long Term Suffering

Damage to Broca's area is not severe long term aphasia, to get the full Broca's Aphasia affect requires damage to the surrounding areas (and those that connect Broca's area to other sections of the brain).

Speech Pathologists

When speech pathologists are brought in straight after strokes they're able to get the patients singing something like happy birthday, and they use the stored tunes and routines to hook people into language and improve their skills. This is effective on most non-fluent aphasics (globals excepted).

Fluent

Fluent aphasia doesn't interrupt the flow of speech. It's also called sensory aphasia.

Fluent aphasics have difficulty monitoring language production, selecting words and organising their thoughts. They're generally unaware of their language problems (as opposed to Non-fluent aphasics); they speak with correction prosody (and often grammaticality) and without listening to the words it can sound like normal language, but the content is semantic rubbish.

Damage to parts of the left cortex behind the central sulcus (near the auditory area in the temporal lobe) is the cause of Fluent aphasia. There are comprehension problems in all modalities.

Wernicke's Aphasia

Also called Jargon Aphasia, Wernicke's is damage to the Angular gyrus, which causes alexia (The inability to comprehend written words).

Their speech understanding is impaired (you can show them objects, ask them to name them and they will come up with something incorrect and show no awareness of that), but their abilities with non-verbal functions are fine; i.e. music comprehension, appreciation and production is fine. This implies that language might be different from other cognitive functions.

Other/Combination Forms

Global Aphasia

This is a combination of Wernicke's and Broca's (damage the whole way from one to the other). This leads to a loss of at least production of language, if not comprehension.

Conduction Aphasia

Characterised by good comprehension of spoken/written language (can perform actions), but an impairment in repeating what was heard, or read aloud what they've read.

They have problems with writing as well, usually incorrect letters or reversed letters.

Transcortical Aphasia

Transcortical aphasia can appear in motor or sensory form.

Motor

Characterised by non-fluent speech and difficulty in naming (anomia)

Sensory

Characterised by fluent speech, ability to echo/repeat, comprehension of spoken/written language is poor.

Damage involves the zone between the temporal and parietal lobes.

Japanese Aphasics

Kanji can be written in Kana, but not vice versa (Kanji you can say the word, then represent syllabically).

Imura (1940) studied a patient with Broca's who was able to write the correct Kanji for dictated words, but was unable to write the same words in the syllabic writing system, the kana. This is odd, because kana is meant to be easier.

It looks like the two different language systems are affected differently. Perhaps they're stored in different areas (where damage is), or they're processed or retrieved in different ways (where damage would be in the connections).

Kanji are located in the left hemisphere, even though symbols are derived from pictures (which is dealt with by the right system). They're abstract figures, and stored in the left hemisphere.

Sign Language and Aphasia

Sign language aphasics suffer the same problems with left hemisphere damage as verbal langauge speakers; even though symbols might originally have been right-brain, they're now left-brain.

Apraxia

When we speak of apraxia, we're talking about people who are unable to do skilled motor movements with their hands in response to a verbal command.

I.e. they understand the command, they can spontaneously move their hand normally (write a note, scratch an itch, etc), but they can't respond to the command.

Pure Word Deafness

Damage to the area between Wernicke's area and the auditory cortex may result in pure word deafness; these patients cannot recognise word sounds as speech, but can comprehend other kinds of sounds.

More specifically, it's caused by bilateral damage to the posterior superior temporal lobes, or disruption of connections between these areas.

A hypothesis for hearing words in other languages is that they would be able to hear them as long as they weren't aware they were words.

Example

Patients might be able to hear music quite clearly, sing a melody, but be unable to recognise that the lyrics are words.

The underlying problem is that to understand speech requires discrimination between specific sounds in the brain.

Acquired Dyslexia and Dysgraphia

The impairment of reading ability as a result of brain damage is known as acquired (dys|a)lexia.

The impairment of writing ability as a result of brain damage os known as acquired (dys|a)graphia.

Broca's Aphasics

In spontaneous writing Broca's aphasics tend to omit function words and inflectional affixes; when writing their production errors (e.g. spoon-poon) are known as paragraphia, and in speech the same errors are known as paraphasia.

Function vs Content:

Broca's aphasics can read semantic substitutions of function words (which they hate and refuse to read). E.g.:

  • 'which' -> 'witch'
  • 'been' -> 'bean'
  • 'our' -> 'hour'

Silent Reading vs Aloud Reading

They can read silently fine, but not aloud.

Wernicke's Aphasics

Their writing production is the same as their spoken; formally very good, but semantically rubbish. Their reading comprehension is also severely impaired; they can see letters and words, but can't make sense of them.

This is clearly a central disturbance of language competence.

Different Types of Dyslexia

Phonological Dyslexia

Grapheme Phoneme correspondence is lost (The ability to use spelling-to-sound rules). This means they can't sound out words. If presented with the word 'blug' they can't pronounce it, they produce another word that is visually similar (e.g. 'blue' or 'bug').

Surface Dyslexia

Do not appear to be able to recognise words as wholes, e.g. they have to read words as sounds every single time. So to read 'hello' they have to sound out 'he-l-lo'.

They don't understand what they read, they understand what they say. E.g. if they see 'sweat' as 'sweet', they'll define it as 'not bitter'.

Combinations

Some maybe unable to read a phrase, but could write it as dictation. They may not be able to read what they have just written. This is known as alexia without agraphia.

Bilingual Brain (An example)

Albert and Obler (1978), Karanth and Rangamani (1988), Wuillemin and Richardson and Lynch (1994) all report greater right brain involvement in language in bilingual people over monolingual people.

Aphasia

Aphasia is more likely to be found following right hemisphere lesions in bilinguals (10% to 2%).

Strokes

Some strokes will wipe out the second language (even if they've been speaking it for 20 years), or sometimes (rarely) it'll wipe out the first language.

Finger-Tapping

When participants are instructed to tap their fingers to a tune with their left hand, and then right, and to speak whilst doing so, much more disruption of speech occurs when tapping the right hand. This applies for bilinguals as well - showing that both languages have at least functionality in the left brain.

Distribution of Speech Areas

Distribution of speech areas in brain appears to be related to:

  • What tasks they're given (comprehension v production)
  • When the second language was acquired
  • What analysis method is used (PET, FMRI, etc)

Agrammatism

From studying other languages, we've discovered that the issue of loss of function words and inflections may be a function of English, and not a true reflection of the issue.

In English affixes are additional, but in Hebrew affixes are cirumfixes (you have to insert vowels into a base word like 'ktv' in order to make it make sense), and in these languages they insert random vowels.

So it's definitely not economy of effort, as the reason for dropping them.