Disorders of visual perception

Question 1

what is the difference between visual illusions and visual perception?

Answer 1

VISUAL ILLUSIONS

• not disorders
• but, they demonstrate that vision is not the perfect representation of external reality

VISUAL PERCEPTION
-susceptible to a whole host of strange perceptual illusions

Question 2

what is the law of meaningfulness?

Answer 2

• aka principle of familiarity
• Gestalt law of perceptual organisation which describes how humans perceive certain combinations of lines, curves and shapes to form a meaningful object

Question 3

why is the brain constantly trying to fill in perceptual gaps

Answer 3

to filter info and make sense of the world

-this happens largely outside of conscious awareness

Question 4

what is neglect?

Answer 4

• failure to report, respond or orient meaningful stimuli presented to OPPOSITE side of where brain lesion is
• patients behave like one half of the world does not exist
• ONLY WHEN the failure cannot be attributed to either sensory/motor defects
• aka hemi-neglect/visual neglect/visuo-spatial neglect/unilateral neglect

-very heterogeneous condition

Question 5

what are personal and extrapersonal neglect?

Answer 5

PERSONAL
-lack of orientation or exploration of the side of body that is contralateral to injured hemisphere (Beschin & Robinson, 1997)

EXTRAPERSONAL
-failure to detect visual and auditory stimuli on the contralateral side (Peru & Pinna, 1997)

Question 6

State the ways in which neglect can be assessed

Answer 6

• cancellation tasks
• line bisection
• copying drawing/draw from memory
• one item test (aka The Personal Neglect Test)

Question 7

State the ways in which neglect can be assessed

Answer 7

• cancellation tasks (star/line)
• line bisection
• copying drawing/draw from memory
• one item test (aka The Personal Neglect Test)

Question 8

what is the Personal Neglect Test?

Answer 8

-requires patient to touch their contralateral hand using ipsilateral hand

given points:
0 = patient promptly reaches target
1 = target is reached with hesitation or search
2 = search is interrupted before target is reached
3 = no movement towards the target is performed

Question 9

which areas of neuroanatomy does neglect affect?

Answer 9

• strong association with right hemispheric lesions
• most common in parietal lobe
• but also: frontal lobe and sub-cortical regions (basal ganglia, thalamus)

Question 10

which areas of neuroanatomy does neglect affect?

Answer 10

• strong association with right hemispheric lesions
• most common in parietal lobe
• but also: frontal lobe and sub-cortical regions (basal ganglia, thalamus)
• different damage linked to different neglect subtypes (Mesulam, 1999)

Question 11

what has insight from neglect patients told us about hemispheric assymetry?

Answer 11

• neglect is far more frequent following damage to right-hemisphere (failure to attend to left side)
• right hemisphere is more specialised for attention than the left (Posner & Peterson, 1990)

Question 12

where is the elaborate representation of the world stored?

Answer 12

in the parietal lobes (according to Bisiach & Luzzatti)

• this suggests that neglect is not just a basic visual defect
• BUT it remains unclear how neglect is brought about (is representation of space itself impaired/is the ability to process it lost)

Question 13

what is attention?

Answer 13

the act or the power of fixing the mind on one thing out of several possible trains of thought occurring simultaneously