11 Perception, Agnosia & Related Disorders

Question 1

retinal ganglion cells - M cells

Answer 1

• 10% of ganglion cells
• large receptive fields
• low spatial resolution
• high temporal resolution
• high contrast sensitivity
• colorblind

Question 2

retinal ganglion cells - P cells

Answer 2

• 80% of ganglion cells
• small receptive fields
• high spatial resolution
• low temporal resolution
• low contrast sensitivity
• color

Question 3

retinal ganglion cells - gamma cells

Answer 3

• 10% of retinal ganglion cells
• heterogeneous properties

Question 4

damage to the optic nerve in one eye leads to …

Answer 4

monocular blindness

Question 5

damage to the optic chiasm leads to …

Answer 5

bitemporal hemianopia (a type of heteronymous hemianopia)
- missing vision in the temporal visual hemifield in both eyes

Question 6

damage to the optic nerve of the right eye that is not crossing at the level of the optic chiasm leads to …

Answer 6

right nasal hemianopia
- missing vision in the left visual hemifield of the right eye

Question 7

damage to one optic tract or the optic radiation leads to …

Answer 7

homonymous hemianopia
- missing vision in the same visual hemifield in both eyes

Question 8

damage to the right parietal optic radiation leads to …

Answer 8

superior left quadrantanopia
- missing vision in the upper left visual quarterfield in both eyes

Question 9

achromatopia

Answer 9

• lingual and fusiform gyrus
• 9% of cerebral visual disorders
• combined with: upper visual field defect, other agnosias

Question 10

agnosia

Answer 10

inability to process sensory information

Question 11

apperceptive agnosia

Answer 11

• inability to distinguish visual shapes and hence, to recognize, copy, or discriminate between different visual stimuli
• unable to copy images
• patients see but don’t understand what they are seeing
• e.g. toxic or anoxic bilateral brain lesions

Question 12

associative agnosia

Answer 12

• inability to recognize objects despite ability to describe visual scenes and classes of objects
• able to copy images
• e.g. know what a fork it but mistake it for a spoon
• defected association between visual and semantic brain areas
• e.g. bilateral temporal lesions HSV

Question 13

prosopagnosia

Answer 13

• lingual and fusiform gyrus
• 3% of cerebral disorders
• combined with upper visual field defect, other agnosias, achromatopia

Question 14

akinetopia

Answer 14

• bilateral lesion to medial temporal gyrus
• combined with lower quadrant field defects, optic ataxia
• neglect

Question 15

neglect

Answer 15

• syndrome with contralateral neglect of sensory stimuli or motor function
• mostly right hemisphere in inferior parietal lobe
• combined with hemianopia, neglect in further modalities, anosognosia (unawareness of a disability)
• spontaneous restitution in 75% within 6 months
• extend correlates with size and location but not with gender or age
• neglect affects other neurological functions