ND - Agnosia, Neglect, Dyslexia and Synaesthesia - Week 3 Flashcards
Consider the three pathways in the visual cortex from the retina. List them and state whether they remain segregated and until what structure.
Magnocellular
Parvocellular
Koniocellular
They remain well segregated until they reach the striate cortex
How many visual areas are they beyond the striate cortex in a macaque brain?
Over 30
What is V1?
Striate cortex
Where is the action pathway? What happens with damage to this area?
It is dorsal (where pathway)
Damage leads to impaired goal-directed action
Where is the perception pathway? What happens with damage to this area?
It is ventral (what pathway)
Damage leads to agnosia
Define agnosia.
Inability to perceive
You can see but do not understand what an object is
Consider a lesion in the dorsal stream. What mistakes would the patient mostly make (2)?
Spatial errors and some orientation errors
What are parallel channels?
They are channels that carry visual signals from the retina into the thalamus and then into the cortex
Describe top-down feedback.
Modulation of afferent signals by processes such as attention
Describe what is meant by the two visual streams and the lobe of the brain it is located, including its anotomical position and primary function.
Dorsal parietal - where or action stream
Ventral temporal - what or perception stream
Describe what is meant by functional localisation. Are things processed independently or not?
different attributes of each object being processed in different cortical areas with different modalities.
They are processed independently.
List functions of the posterior parietal cortex.
Helps to bind different attributes of an object together
Gates inputs into the ventral stream
Important for reading (linked to dyslexia)
What does the posterior parietal cortex play a central role in?
Directing attention to spatial locations
What can predict later reading failure?
Pre-reading phonological skills
What do dyslexic children have difficulty with (2)?
Discriminating syllables and rapid acoustic stimuli
Briefly describe the main components of the dual-route model of reading and name each route. Describe what kind of words each route is used for.
Direct lexical - visual word recognition, for familiar everyday words
Phonological - phonic assembly, for new and non-words like torp, sint, guk
Are phonological representations themselves normal or deficits in dysexlics? Explain.
The phonological representations themselves are normal, it is access to them that is defective
Does reading affect auditory perception?
Yesd
What can improve phonemic awareness?
Orthographic training
Consider a magnetoencephalography scan when reading is taking place. Where does activation start? Is it bi- or unilateral? Where does it extend to and what can this region be considered? What does it do?
Activation starts in the occipital lobes bilaterally. It extends to the left occipito-temporal region, which is the brain’s letterbox that extracts word forms from the visual scene.
Describe a possible genetic basis for dyslexia, including chromosome number and the gene associated.
Gene translocation on chromosome 6 in the HLA region
What is a possible morphology difference in dyslexic brains compared to normal?
Abnormal hemispheric symmetry of the planum temporale
How is contrast sensitivity different in dyslexics? What is this evidence for?
Poorer contrast sensitivity at low spatial frequencies, evidence for an abnormal magnocellular pathway in dyslexics
What do low contrast stimuli elicit in dyslexics compared to normal?
Poorer visual evoked potentials
What are the magnocellular layers in the LGN like in dyslexic brains compared to normal?
They are abnormal
Is visual motion sensitivity normal or impaired in dyslexics? What tools can demonstrate this (2)?
It is impaired
- psychophysically
- as shown with fMRI
Learning to read a process of training what?
The attentional spotlight to move sequentially along the visual scene
Describe how visual search mechanisms operate as they have developed in evolution (2). Give two reasons why it is so evolutionarily. How does this affect training the attentional spotlight?
They are random and do not have memory
-to reduce computational load of having to keep track of every object at every location
-so as not to miss real changes in the visual scene
This makes training the attentional spotlight difficult
What is the attentional spotlight dependent on (2) and what does impairment to these lead to? What does this mean for dyslexics?
Depends on integrity of the M pathway and the dorsal stream.
Damage to these or the parietal cortex can lead to reading problems.
This means dyslexics will perform poorly in visual search tasks.
Are both attentional engagement and disengagement poorer in children or just one (or none)?
Both are poorer in dyslexic children
What does an fMRI scan during reading reveal about dyslexic brains when reading is occurring? Which components of the dual-route model is affected? What can poorer activation of these areas possibly be due to?
Poorer activation in the temporal lobe and posterior cortical areas
These areas are associated with the phonological assembly route
The poorer activation could be due to downstream effects due to a lack of luent temporal sequence of graphemes
How much would a normal child read in one day compared to a severely dyslexic child?
A normal child would read as much in one day as a dyslexic child would in one year
What are the two main pathways connecting brain regions involved in reading? What are their sizes correlated with? Exposure to what makes profound changes to these pathways?
Left superior longitudinal fasiculus and left arcuate fasiculus
Their sizes are correlated with reading scores
Exposure to language makes profound changes to these tracts
Define synaesthesia. Give some examples.
Stimulus in one sensory modality or submodality causing perception in another sensory modality or submodality
Hearing music accompanied by seeing colours
Shapes associated with odours
Numbers or letters having colours
What may synaesthesia be due to?
Lack of pruning during development between cortical areas processing different modalities or submodalities.
