#14072 - Language - Psychology

To what extent is the brain lateralised for language? Illustrate your answer with reference to patients with brain damage.

What is the evidence supporting the view that: (i) the language we speak influences our thoughts and perceptions; (ii) the age at which we acquire a language influences our language ability?

What is the evidence supporting the view that there are critical periods for language acquisition?

Provide definitions for language, phonology, semantics and grammar (or syntax). Describe the grammatical abilities of patients with (i) Broca’s aphasia and (ii) Wernicke’s aphasia.

Definitions

1. Language

2. Phonology:

3. Semantics: broadly defined as the meaning of linguistic expression

4. Grammar/ syntax- the rules/grammar that specify how words can be combined into sentences in a given language

Auditory paths

-There are two routes for perceiving and producing speech

• Lexical semantic processing; “what route”

  • Ventral to the Left primary cortex – this route makes contact with structures important for semantic memory

• auditory motor correspondence “how route”

  • Auditory , motor, visual aspects of speech converge

  • Region is linked to motor theory of speech perception as region is active when silently articulating a phrase/ thinking about a phrase

Functional imaging studies have shown that primary auditory cortex of both left and right hemispheres responds equally to speech and other types of auditory stimuli

This suggests divergence at a lateral cortical stage- beyond the auditory cortex, humans begin to show a greater left hemisphere responsiveness for speech relative to non-speech along the what route of temporal lobes

• Scott et al 2000- showed increased activity in left temporal region in intelligible relative to intelligible speech

Pure word deafness: found following damage to the left hemisphere-these patients are able to identify environmental sounds and music but not speech- these patients are able to produce speech but heard speech appears to be too fast/ distorted

Broca’s area

• Broca’s patient Leborgne only utterance was word ‘Tan’ – despite this language deficit Lebornge was capable of comprehending spoken and written language

• Broca did an autopsy on Leborgne and discovered large lesion of left inferior prefrontal cortex- which is now known as Broca’s area

• Deficit:

  • Expressive difficulties

    • language is slow and laboured

    • lacking in grammatical structure

    • speech also lacks intonation and inflection of normal language

  • Comprehension difficulties

    • Comprehension of spoken language normal

    • Problem in understanding grammatically complex language

This shows broca’s area is important for expression of language and understanding of grammar

Wernicke’s area

• Brodmann area 22- superior temperol gyrus

• 1874 Wernicke discovered that damage to region of left temporal lobe- posterior to auditory cortex was associated with deficit in language comprehension and speech that is meaningless or devoid of intelligible content/meaning

• So damage to Wernicke area is associated with receptive difficulties speech that is fluent and grammatically content but is utterly nonsense –fluent aphasia

Wernicke-Gerschwind model of language

• Geschwind proposed that when we hear spoken language sounds are first processed by auditory cortex which then passes its input to Wernicke’s area where sounds are decoded and comprehended.

• Then if a response is necessary Wernicke’s area further translates thought processes into verbal responses which are transmitted to Broca’s area via the left articulate fasciculus. In Broca’s area the necessary neurons for articulation and complex muscle co-ordination so that appropriate spoken language reply can be voiced

• -Wernicke is connected to Broca’s area via the arcuate fasciculus and loss of this results in conduction aphasia – this refers to difficulties repeating words just heard

Spoken word recognition- Wernicke’s

• matching some aspect of an acoustic form to a stored set of spoken words that comprise the set of known word’s speaker’s vocabulary- this store of words is known as phonological lexicon and the matching process is called lexical access

  • Cohort model- Marslen-Wilson and Tyler – 1980- Theory states that in lexical access a large number of spoken words are initially considered as candidates but words get eliminated as more evidence accumulates. The point at which acoustic input unambiguously corresponds to only one word- uniqueness point

• Semantic meaning of words-coded by the ventral route for speech comprehension- temporal lobes. Within these regions there is a sensory functional distinction- describes semantic categories differ in the extent to which functional vs sensory information is presented

  • Some objects defined by sensory properties- colour, shape, four legs, intimate objects such as tools defined by their function

  • Functional imaging has shown different regions of temporal cortex light up accordingly

• Another model for semantic meaning Is categorical organisation into action based, shape based, movement based rather than a dichotomous separation into sensory/functional. These categories include food, colours, body parts, action and verbs, proper names and numbers

• -Connections from parietal to frontal region join how speech circuit with what circuit- this forms the articulatory loop- this acts as a short term memory store for verbal material- information in store is refreshed by sub-vocal articulation

Syntax

-The process of assigning a syntactic structure to words is termed as parsing

-Semantic dementia atients have shown that they can decide whether a sentence is grammatical but don’t understand the meaning

Speech production

-Speech production involves translating an intended idea into a sentence structure and retrieving and producing the appropriate words

-The first stage is that words must be selected based on its meaning that one wishes to convey- this is known as lexicalisation- this is constrained by knowledge of the listener. 2^nd stage the grammatical properties of word must be retrieved and specified-e.g noun, verb, gender of word 3^rd stage- syllables, phonemes and articulatory patterns

-Speech errors- E.g Freudian slip- Freud believed that speakers repress their true thoughts durin conversation and these could be revealed by speech errors

Reading

Visual word recognition

-visual process of recognising a word as familiar is not strongly affected by word length

-Visual word recognition appears greater that it’s constituent letters

-If one is asked to detect presence of single letter, performance is enhanced if letter is presented in context of a word than in a random letter string- this is known as word superiority effect- this suggests that there are units of representation corresponding to letter clusters that influence visual recognition of letters and words

-To investigate word recognition – lexical decision in which participants must make a two way forced choice judgment about whether a letter string is a word or not. One theory is that the lexical decision is performed by matching words- this is known as visual lexicon

-These studies suggest that word recognition is similar to a top down model

-Visual word form area- located in left mid occipitotemporal gyrus/fusiform gyrus. Meaningless shapes that are letter like don’t activate the region. This suggests that neurons have become tuned to visual properties of known letters and common letter patterns. This area also responds to non-words made up of common letter patterns as well as real words

Peripheral dyslexia

Disrupt processing up to the level of computation of a visual word form

Alexia

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