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READING WORDS AND ITS DISORDERS :PENCIL2: D+L2 LECTURE 6 - Coggle Diagram
READING WORDS AND ITS DISORDERS
:PENCIL2:
D+L2 LECTURE 6
Writing and reading
Evolutionary unexpected, experience-dependent abilities, relying on aspects of spoken language processing and other skills that may have genetic components (developmental dyslexia)
5.1 million adults are functionally illiterates in England
Writing represents units of spoken language (words, syllables, sounds)
Brain isn’t evolutionarily prepared for reading.
Phonological/visual processing impairment.
Reading is a crucial aspect for success in life.
Visual word processing
We read words in many forms, we extract or generalise the typical features.
Abstract level of representation - visual lexicon
Recognized by the same part of the brain.
Accessing visual word forms: Serial vs Global recognition
Serial
E.g. r e a d i n g
Global
E.g. Aoccdrnig to rscheearch at Cmabrigde Uinervtisy...
Global recognition in RVF / Left Hemisphere
Words presented in the RVF are processed faster, they project directly to the LH.
This is because there is global rapid visual recognition in the LH.
When words are presented in the LVF (and thus directly projected into the RH), the processing is more serial, and words are recognised by identifying letters and sharing them with the LH (via corpus callosum) for word identification.
This is why the number of letters in a word matters when words are presented in the LVF, and processing is slower for longer words.
How do we explain these different reading skills?
Triangle model
Accounting for behavioural findings
Visual processing: Orthography --> Semantics --> Phonology
Brain-based model
Is there a visual lexicon 'area' in the brain?
In reading we need to process visual input, so we need to add nodes and pathways to brain processing streams.
There are several cognitive models of reading that have been inspired mostly by behavioural findings.
One of these models is the triangle model, which posits three main centres or nodes for
orthographic
,
phonological
and
semantic representations
.
These nodes are interconnected and can be simultaneously activated in a given task, or they can influence each other.
For reading out non-words, we just use the mapping from orthography to phonology.
When meaning is involved, we also use the semantic node.
Interestingly, cognitive models predict that there should be some brain area processing the VISUAL LEXICON, the set of word forms that we are familiar with, irrespective of font, orientation and type case.
Reading: The Visual Word Form Area (VWFA)
An area in the fusiform (occipito-temporal) gyrus responds to:
Words more than false-fonts or consonant strings (chair vs. ckmn)
Upper and lower case equally: (chair vs CHAIR vs cHaIr)
Real words more than non-words sounding the same (taxi > taksi)
Orthographic identity of the word
Imaging studies typically compare across two or more conditions, and deciding which conditions to compare is the critical aspect of the experimental design that allows you to infer meaningful conclusions.
So the findings are restricted to what you used as a comparison, and difficult to generalize to other comparisons not tested.
Visual Word Form Area in LH responds equally strongly to right or left visual field presentation.
Located in the fusiform gyrus
Because fMRI does not have good temporal resolution, we cannot “see” whether the information gets to the LH faster or slower depending on the visual field.
This data shows that whether or not the words are presented in the RVF or the LVF, it is activity in the left VWFA that responds more strongly to words in comparison to consonant strings.
This suggests that word recognition or identification is performed in the LH.
VWFA in LH responds equally strongly to right or left visual field presentation
Both presentations of key words into different visual fields should give you more activity in the left than right hemisphere.
Because that will suggest that the visual word form area is really part of the visual reading system directly connected to the language system of the left hemisphere.
Because in the right hemisphere there isn’t anything linguistic for that visual information to be connected to, since language centres lie in the left hemisphere.
In the image above, RH and LH are reversed.
Only see a strong response to the real words in the fusiform gyrus in both left and right visual field presentation.
Meaning that word recognition is done only in the left hemisphere.
VWFA: Adaptation from learning / reading experience
Dehaene and Cohen (2001)
Comparing literates, illiterates and ex-illiterates.
Claim: VWFA become specialised for visual word recognition.
Example of experience affecting brain development.
Results from an fMRI study comparing different groups of literates (from Brazil and Portugal, “B” and “P” in the legend), in comparison to adult learners (people who learn to read as adults = Ex-illiterates), and illiterates.
The main point of this study is that these groups show different degrees of literacy skills or reading skills.
Near 0 performance means they can read a few words per minute (very slow!), whereas near 100 performance means participants can read about 100 or 150 words per minute.
This shows that as the reading performance increases across the groups, activity in the VWFA increases in response to written sentences.
The graphs at the bottom show the same information in the horizontal axis, but on the vertical axis they show activity in the VWFA in response to a variety of visual objects (faces, houses, etc.).
These graphs show that illiterates show stronger activity in the VWFA in response to faces, houses or checkers than literates.
This suggests that the response of the VWFA to letters and words becomes specialised the more experience one has with reading.
VWFA activity changes as a function of reading expertise.
So it can be argued that through experience, the brain adapts an area originally dedicated to visual object/face processing to letter recognition and reading.
Data consistent with adaptation as a function of expertise comes from blind Braille readers, who also show a stronger response in WFA when recognizing words in the tactile modality, compared to non-words.
Adaptation also leads to establishing stronger links between the phonological and orthographical forms of the words, so that when you activate one form (e.g., you hear a word and activate its sound representation), the other form (e.g., the visual form) will also be activated to some degree, particularly in highly skilled readers.
This is because with reading experience, we become better and better in reading aloud (this is what children do all the time at school), so that upon seeing the words, we automatically activate its pronunciation and vise versa (hearing the word will activate the visual from).
VWFA remains controversial
Consider the following:
Skilled readers also activate the VWFA to letter strings and auditory words.
Skilled readers also activate the VWFA for object meaning.
Blind Braille readers also have WFA, which does not require visual input (modality-independent representation)
What remains controversial is whether there is regional functional specificity.
Because the conclusions we can make from imaging data depend on the specific comparisons made, some studies have found that the VWFA also responds to object pictures during naming.
This can be interpreted as meaning that this region has some role in visual object processing as well as reading.
So whether this area is specifically dedicated to word form is debated, as the title of Price & Devlin’s (2003) paper indicates.
“The Myth of the Visual Word Form Area”
Reading network in the congenitally blind
Visual cortex is active in
Braille
reading, along with fusiform gyrus and parietal cortex.
Listening to words also activates posterior “visual” areas, despite an intact auditory cortex
Reorganisation of the occipital cortex as a function of experience which varies with developmental stage
As in sighted people, there are associations of word sounds to word forms in sighted, congenitally blind and late blind (adults 17-36)
What might. be going on...
Results suggest an interactive network where over-learned associations between sounds, letters and meaning activated each other to different degrees.
Interactivity explains different levels of activation, where the regions directly relevant to the task (e.g., auditory cortex for sound repetition) are more active, but other interconnected regions also become active to some degree.
The structure of the connections may also play a role, e.g., VWFA lies in the connection from vision to semantics.
Automatic links between nodes are established with learning, so sounds also activate VWFA
Phonology and orthography are linked together, fire together, meaning that it could be the case that whenever you hear the phonology you also activate the orthography.
Even if the task doesn’t require the activation of orthography.
Interactivity within the network may explain the brain evidence as a function of task
VWFA is located in the mapping from vision to meaning (ventral route) and connects to sound processing regions, so other active regions spread activity to it.
VWFA results from developing expertise in reading, but it may be not exclusively involved in reading or in visual processing.
Ventral and dorsal routes in reading
Putting the two routes together – in sounding out “kal” you use the dorsal route to convert letters to sound, after recognising the letters.
Some researchers claim that the phonological buffer (angular gyrus) performs the transformation from letters to sounds for words and non-words.
In reading a word silently, you use the VWFA to identify the word, this information will be relayed forward into the temporal lobe to access the meaning of the word.
There will also be some “residual” or associative activation of the phonological form (or pronunciation) of the word can also be automatically activated in skilled readers, although there will be no transformation into a motor output
Disorders of reading
Developmental Dyslexia
Difficulty in learning to read below standard appropriate to age
No apparent issue with spoken language
Hereditary component
Phonological impairment: decomposing words into individual sounds (phonological word representations)
How is it a phonological impairment if spoken language is fine?
Early phonological deficit prior to schooling --> Later phonological deficit at schooling --> Reading deficit
Developmental dyslexia is not recognised in a child until the child starts reading, because at that point, they need to decompose the words into individual sounds to match to letters.
This is what dyslexics find difficult.
Up to that point, they have learned the words as global sound representations, and following global acoustic cues to distinguish between words.
Although their vocabulary may be poorer than typically developing children, this is not recognised until they start school.
Phonological awareness is impaired
Which words start with a different sound: bit, bat, cat?
Say cat without the first sound, what word rhymes with pie?
Check dyslexia test in VLE and tutorial
Deficits: non-word repetition, naming pictures (expressive vocabulary), phonological working memory, rhyming
Phonological awareness and the ability to individuate sounds within words is difficult for dyslexic children.
This can be seen as a problem of sound decoding, but it probably also involves some aspects of phonological working memory:
i.e., the ability to hold and manipulate sounds in working memory
Dyslexic brain in children
Deactivation in reading network, particularly phonological route
Often over-activation in left inferior frontal gyrus
Differential grey and white matter volume: anatomical structures and connections
Comparisons in fMRI studies across dyslexics and typical children shows deactivation of the phonological route in dyslexics.
White and gray matter volume also appear different compared across these groups.
Developmental Dyslexia: Are there improvements?
Some dyslexics often reach good levels of reading
Adults may develop compensatory strategies and networks to read
Hypothesis: the RH assumes some of the functions performed by the LH in typical readers
Adult dyslexics show over-activation of the right Broca’s area.
Another case of language network reorganization.
Acquired phonological dyslexia (due to stroke)
Fine visual lexicon and comprehension, but can’t pronounce unfamiliar words.
Familiar words are read better than non-words
Non-words are misread as a familiar word
E.g. “fint” → /fine/; “poat” → /boat/
Short-term memory for speech sounds and manipulation of sounds (phonological buffer)
Impaired grapheme-to-phoneme conversion in reading or writing.
Acquire phonological dyslexia is similar to developmental dyslexia.
Patients are going to have trouble with mapping letters to sounds in non-words.
The letter-to-sound conversion is damaged, so they need to recognise the word as something they know, and attach a meaning to it, to be able to retrieve its pronunciation or a learned motor plan.
This is why they misread non-words as words.
They use some sort of global mapping between the meaning and the pronunciation of a familiar motor plan (circumventing the dorsal route), but this can only occur for familiar words.
So the patients are heavily relying on the ventral route, due to damage to the dorsal route.
They also have trouble manipulating and holding sounds in memory, a function associated with a phonological buffer in the angular gyrus.
Notice that damage to different areas can give rise to similar symptoms, suggesting the damage in various parts of the language network can result in similar deficits, consistent with interactivity and connectivity within the language network.
Damage to one area will also affect other areas that typically interact and communicate with it.
Reading in brain and behaviour
Reading is a complex task involving a network of brain regions talking to each other.
It is difficult to learn for millions of people who often remain untreated.
Understanding the mechanisms underpinning reading is necessary to develop successful intervention, which are particularly effective early on in development (e.g. training in phonological tasks)