ND - Agnosia, Neglect, Dyslexia and Synaesthesia - Week 3

Question 1

Consider the three pathways in the visual cortex from the retina. List them and state whether they remain segregated and until what structure.

Answer 1

Magnocellular
Parvocellular
Koniocellular
They remain well segregated until they reach the striate cortex

Question 2

How many visual areas are they beyond the striate cortex in a macaque brain?

Answer 2

Over 30

Question 3

What is V1?

Answer 3

Striate cortex

Question 4

Where is the action pathway? What happens with damage to this area?

Answer 4

It is dorsal (where pathway)

Damage leads to impaired goal-directed action

Question 5

Where is the perception pathway? What happens with damage to this area?

Answer 5

It is ventral (what pathway)

Damage leads to agnosia

Question 6

Define agnosia.

Answer 6

Inability to perceive

You can see but do not understand what an object is

Question 7

Consider a lesion in the dorsal stream. What mistakes would the patient mostly make (2)?

Answer 7

Spatial errors and some orientation errors

Question 8

What are parallel channels?

Answer 8

They are channels that carry visual signals from the retina into the thalamus and then into the cortex

Question 9

Describe top-down feedback.

Answer 9

Modulation of afferent signals by processes such as attention

Question 10

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.

Answer 10

Dorsal parietal - where or action stream

Ventral temporal - what or perception stream

Question 11

Describe what is meant by functional localisation. Are things processed independently or not?

Answer 11

different attributes of each object being processed in different cortical areas with different modalities.
They are processed independently.

Question 12

List functions of the posterior parietal cortex.

Answer 12

Helps to bind different attributes of an object together
Gates inputs into the ventral stream
Important for reading (linked to dyslexia)

Question 13

What does the posterior parietal cortex play a central role in?

Answer 13

Directing attention to spatial locations

Question 14

What can predict later reading failure?

Answer 14

Pre-reading phonological skills

Question 15

What do dyslexic children have difficulty with (2)?

Answer 15

Discriminating syllables and rapid acoustic stimuli

Question 16

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.

Answer 16

Direct lexical - visual word recognition, for familiar everyday words
Phonological - phonic assembly, for new and non-words like torp, sint, guk

Question 17

Are phonological representations themselves normal or deficits in dysexlics? Explain.

Answer 17

The phonological representations themselves are normal, it is access to them that is defective

Question 18

Does reading affect auditory perception?

Answer 18

Yesd

Question 19

What can improve phonemic awareness?

Answer 19

Orthographic training

Question 20

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?

Answer 20

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.

Question 21

Describe a possible genetic basis for dyslexia, including chromosome number and the gene associated.

Answer 21

Gene translocation on chromosome 6 in the HLA region

Question 22

What is a possible morphology difference in dyslexic brains compared to normal?

Answer 22

Abnormal hemispheric symmetry of the planum temporale

Question 23

How is contrast sensitivity different in dyslexics? What is this evidence for?

Answer 23

Poorer contrast sensitivity at low spatial frequencies, evidence for an abnormal magnocellular pathway in dyslexics

Question 24

What do low contrast stimuli elicit in dyslexics compared to normal?

Answer 24

Poorer visual evoked potentials

Question 25

What are the magnocellular layers in the LGN like in dyslexic brains compared to normal?

Answer 25

They are abnormal

Question 26

Is visual motion sensitivity normal or impaired in dyslexics? What tools can demonstrate this (2)?

Answer 26

It is impaired

• psychophysically
• as shown with fMRI

Question 27

Learning to read a process of training what?

Answer 27

The attentional spotlight to move sequentially along the visual scene

Question 28

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?

Answer 28

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

Question 29

What is the attentional spotlight dependent on (2) and what does impairment to these lead to? What does this mean for dyslexics?

Answer 29

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.

Question 30

Are both attentional engagement and disengagement poorer in children or just one (or none)?

Answer 30

Both are poorer in dyslexic children

Question 31

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?

Answer 31

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

Question 32

How much would a normal child read in one day compared to a severely dyslexic child?

Answer 32

A normal child would read as much in one day as a dyslexic child would in one year

Question 33

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?

Answer 33

Left superior longitudinal fasiculus and left arcuate fasiculus
Their sizes are correlated with reading scores
Exposure to language makes profound changes to these tracts

Question 34

Define synaesthesia. Give some examples.

Answer 34

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

Question 35

What may synaesthesia be due to?

Answer 35

Lack of pruning during development between cortical areas processing different modalities or submodalities.