Visual Dysfunction wk11

Question 1

the motion coherence task

Answer 1

signal dots= dots all uniformly moving in the same direction
- Task will ask what direction they are going in, increasing number of noise dots as levels get harder

Question 2

what conditions have elevated thresholds for the elevated motion coherence task

Answer 2

• Williams syndrome
  -Autism
  -Dyslexia

typically need higher coherence to spot the general direction

Question 3

issues within dyslexia

Answer 3

issues with reading and spelling

Question 4

what are issues in dyslexia due to?

Answer 4

due to impairments with the Magnocellular (dorsal) part of the visual system (involved in motion based timing and rhythm via MT and STS).

reduced size of cells in magnocellular layers in the LGN

Question 5

Issues with the magnocellular hypothesis

Answer 5

only about 30% of dyslexic people show difficulties with motion perception meaning magnocellular differences cannot CAUSE dyslexia

testing theory is hard as we dont always have adequate non magnocellular comparison tasks, it may be that higher threshold results are due to higher order processes later on rather than LGN

Question 6

cornelissen (1995), dyslexia, and motion coherence

Answer 6

found dyslexic people struggle with motion coherence - require a 3% increase in dots vs controls in order to perceive direction

Question 7

dyslexia and brain regions

Answer 7

Found a amore gradual increase in sensory parietal lobes when dyslexic children made a decision

Deficit may be about decision making areas/activity that appears to be different, beyond early LGN processing

Question 8

what does autism impact?

Answer 8

social awareness and involves heightened sensory awareness, with an excessive attention to detail and change

restrictive and repetitive behaviors and interests

Question 9

autism and motion coherence

Answer 9

show higher motion coherence thresholds than typical children, revealing an impaired ability to detect coherent motion.

though this effect is consistent, effect size is small

Question 10

Autism and the weak central coherence

Answer 10

elevated motion coherence thresholds attributed to difficulty integrating parts into a whole

instead of combining info about all the dots in a motion task, they focus on a small pool (e.g. a row) to focus on local details

explains why they are less susceptible to illusions but because motion tasks involves combining info, they cannot

Question 11

Autism and weak central coherence neural links

Answer 11

linked to reduced functional connectivity, stronger local connectivity but weak long range neural connections

causing reduced top down modulation/ bias to local info

Question 12

why are motion coherence thresholds elevated in autistic children - explanations

Answer 12

• reduced sampling/global pooling
• higher internal noise /variability in neural firings leading to imprecise estimation of each local direction

-reduced segregation of signal from noise / the inability to ignore noise

Question 13

Direction integration task

Answer 13

SD of dots gets bigger and we weight all directions equally ( no noise signals)

requires integration rather than separation of basic motion coherence task

Question 14

Equivalent noise modelling and what measures does it give

Answer 14

gives estimates of internal noise and sampling

Question 15

autism motion coherence task vs direction integration task (study)

Answer 15

autistic children do sig better in a DIT task compared to controls when SD is wide + just as percsise as controls in a low SD task

MCT dont have a sig between groups , so corresponding advantage doesn’t translate

suggesting that autism-related difficulties may stem more from signal-noise segregation than from integration itself (filtering issue)

Question 16

autistic children and their levels of internal noise and sampling

Answer 16

Autistic children had slightly higher levels of internal noise but not sig, but also they had increased sampling so they’re able to combine more dots then controls

they can average motion over a greater directional range

goes against weak coherence theory

Question 17

how can the associations between dyslexia, schizophrenia, and autism be explained?

Answer 17

Dorsal stream vulnerability

Because our dorsal stream is slower to develop than the ventral, it makes their functions more vulnerable to atypical development in these conditions

shown as motion (D) thresholds start higher than form (V) tasks

Question 18

dorsal stream vulnerability critique (tasks)

Answer 18

is may be that the tasks between form and motion tasks are too dissimilar to each other

found that when better matching tasks there was a reduced performance in both types of tasks

so conditions may not be only dorsal specific

Question 19

Dorsal stream vulnerability critique (neural)

Answer 19

Dorsal stream isn’t a single neural pathway, it interlinks and overlaps with networks

There could be different parts of the dorsal stream that are affected in different conditions

Question 20

Dorsal stream vulnerability challenges

Answer 20

not all dorsal stream tasks are impaired in neurological conditions- sometimes enhanced ability (e.g. autism and DIT task )

Just because these conditions have a common visual difference/thresholds doesn’t mean they have the same cause –> we have condition specificity ( autism= increased sampling, dyslexia- increased internal noise)

Question 21

What is the pattern glare test

Answer 21

Task that helps show that there are some people that are more sensitive to some types of info than others

There is a set of stripes patterns in different spatial frequencies (how thick)

People then asked if they see any distortions when looking at the image or discomfort

Question 22

Visual stress definition and triggers

Answer 22

discomfort/pain when looking at certain visuals to varying degrees

triggers may be flickering and high contrast patterns

common in photosensitive eplilepsy,migrane,dyslexia

Question 23

what is photosensitive epilepsy?

Answer 23

PE is a condition where seizures are triggered by temporal frequencies

e.g., stroboscopic flashing and striped patterns

Question 24

demographic factors for seizures and PE

Answer 24

4% of population have epileptic seizures at some point

4% of these are triggered by visual stimuli- photosensitive epilepsy

Question 25

what are migraines?

Answer 25

are severe prolonged headaches accompanied by nausea, photophobia and phonophobia.

Question 26

similarity between PE and migraines

Answer 26

visual triggers for migraines may be similar to those for PE, suggesting a common mechanism.

Question 27

what can migraines be preceded by?

Answer 27

can be preceded by auras – ‘hole’ in the fovea which spreads to the periphery in a striped pattern can sometimes be visual

Question 28

neural basis for migraines

Answer 28

visual cortex has evolved to process natural images efficiently but some stimuli deviate from natural statistics leads to excessive excitability in the cortex with the brain working harder to process the stimuli

Question 29

EEG traces in photosensitive eplilepsy

Answer 29

As soon as we have an onset of a flash stimulus, we get higher negative amplitudes in signal, increased excitability specifically when colour chromaticity speration is high

Question 30

how is visual stress alleviated in dyslexia?

Answer 30

alleviated by using coloured overlays for paper and wearing precision-tinted lenses. however not all with dyslexia suffer from visual stress (vice versa ) +lack of evidence of effectiveness

Question 31

for and against visual stress

Answer 31

long history of controversy created skepticism for the condition with lack of research broad symptoms are characteristic of many other conditions, which have not been screened for. so visual functioning can vary across the population, just more common in certain conditions