Visual Dysfunction, Objects, Size, and Shape

Question 1

issues within dyslexia

Answer 1

issues with reading, spelling, and event sequencing

Question 2

what are issues in dyslexia due to?

Answer 2

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

Question 3

cornelissen (1995), dyslexia, and motion coherence

Answer 3

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

Question 4

what can explain the origin of dyslexia?

Answer 4

cerebellar deficits, as the Magnocellular system terminates in the Cerebellum

Question 5

what can lead to impaired temporal processing?

Answer 5

issues with Magnocellular systems and cerebellar functioning

Question 6

what is schizophrenia characterised by?

Answer 6

disorganised thinking and speech, poor memory, auditory hallucinations, and poor emotional and social function.

they also struggle to detect motion

Question 7

what does autism impact?

Answer 7

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

Question 8

autism and motion coherence

Answer 8

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

Question 9

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

Answer 9

possible that the dorsal system (includes STS) is involved in processing motion, event timing, and social stimuli, which are all disrupted in these conditions vs. biologically fragile dorsal pathway.

Question 10

what is photosensitive epilepsy?

Answer 10

PE is a condition where seizures are triggered by temporal frequencies, e.g., stroboscopic flashing at 15HZ, and visual frequencies, e.g., 12pt line separation.

Question 11

demographic factors and explanation of PE

Answer 11

experienced by 4% of the population due to increased excitability in the visual system.

EEG traces show the onset of a flashed stimulus causes widespread increase in electrical activity during seizures – highlighting the role of cortical excitation in PE.

Question 12

what are migraines?

Answer 12

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

Question 13

similarity between PE and migraines

Answer 13

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

Question 14

what are migraines characterised by?

Answer 14

excessive excitability in the cortex and failure to inhibit excessive inhibition.

this leads to neuron fatigue and dilated blood vessels to avoid reduced oxygen, resulting in the later headache.

Question 15

what can migraines be preceded by?

Answer 15

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

Question 16

what is visual stress (meares-irlen syndrome)?

Answer 16

shares symptoms with these conditions, and affects 20% of the population. They struggle to read printed text and see coloured blotches appearing in the text.

Question 17

how is visual stress alleviated?

Answer 17

alleviated by using coloured overlays for paper and wearing precision-tinted lenses.

filters are successful by preventing excitation spread from local areas to other areas of the cortex

Question 18

huang (2011) and prescribed lenses

Answer 18

FMRI showed reduced cortical activity in V3 (processes motion) and V4 (processes colour) when wearing prescribed lenses

Question 19

for and against visual stress

Answer 19

long history of controversy and anecdotal evidence created skepticism for the condition.

broad symptoms are characteristic of many other conditions, which have not been screened for.

Question 20

what is lateral occipital cortex (LOC) involved in?

Answer 20

combining shapes into whole objects

posterior LOC - detects parts of objects
anterior LOC - whole object recognition

Question 21

classic ‘bottom-up’ view of vision

Answer 21

vision starts on the surface of the retina and works via increasing complex stages in even higher brain areas, towards some behavioural goal

Question 22

how does the bottom-up view work for object recognition?

Answer 22

segment them from the background, identify contours, build contours into object outlines, and then recognise objects.

Question 23

what is figure-ground segmentation?

Answer 23

involves separating objects from their background before they can be recognised. Contrast-sensitive neurons in each sub-system are responsible for this

Question 24

what is responsible for figure-ground segmentation?

Answer 24

contrast-sensitive neurons in each sub-system are responsible for this

• RGC/LGN cells find object edges
• Orientation-contrast cells – texture-segmentation
• Motion-contrast cells – figure-ground for motion
• Disparity neurons – direct-object segmentation

Question 25

what do illusory contours demonstrate?

Answer 25

the importance of top-down influences to fill in missing information, by perceiving a contour where no line exists at around 8m for static displays.

Question 26

how do illusory contours occur?

Answer 26

occurs via the receptive fields of V2 cells, which detect the presence of the illusion of an object.

Question 27

what are V2 receptive fields constructed from?

Answer 27

output of V1 hypercomplex cells, which detect line endings.

receptive fields at line endings will respond more strongly, which creates the perception of contour.

Question 28

what is contour integration?

Answer 28

ability to link short sections of a contour to form a longer contour, to create the impression of a whole object.

Question 29

when and how does contour integration occur?

Answer 29

occurs due to the long-range excitatory connections between cells with the same orientation, but different positions.

takes place in area V1 and develops around 2y.

Question 30

role of form cells in V4

Answer 30

transform local contour information into coherent object perceptions

by selectively responding to contour features and integrating this information into representations of objects

Question 31

what are geons?

Answer 31

there are 36 geons (geometric axons) that represent fundamental shapes to construct objects

Question 32

what must occur between V4 and LOC?

Answer 32

the ability to construct an object

Question 33

how is LOC involved in shape recognition?

Answer 33

by integrating information across different areas, rather than specific object identification.

Question 34

what do object classification tasks suggest about vision?

Answer 34

vision is much easier via top-down view –

as higher-order information influences lower-down information by spotlight of attention to speed up recognition

Question 35

how does top-down information refine the guesses of the visual system?

Answer 35

compares predictions to higher-order information

Question 36

what does redundancy show?

Answer 36

learning is easier for predictable words and text (top-down information)

Question 37

what top-down connections (_______ and ______) can guide attention to speed up recognition?

Answer 37

knowledge and expectations

Question 38

shepard (2009) table top illusion

Answer 38

3D shape perception is important for the table top illusion,

as the retina sees the 2D line drawings as different, this means the brain assumes the 3D shapes must also be different

Question 39

effect of autism on the table top illusion

Answer 39

less susceptible to the illusion, as they rely more on sensory experience and less on top-down influences

they believe the tables are the same size

Question 40

how can size constancy be distorted?

Answer 40

beuchet chair and ames room
- retinal image is not scaled to the perceived distance

Question 41

what happens when the perceived distance is too small?

Answer 41

we perceive things smaller than they really are

Question 42

what does forced perspective employ?

Answer 42

optical illusions to make objects appear a different distance than reality.