9.5 and 9.6 Flashcards
(54 cards)
What is the key question left unanswered by anatomical and physiological studies of brain systems?
How do all of the cells in these systems act together to produce a particular function?
What is one way to evaluate the visual system’s function?
Evaluate what happens when parts of the visual system are dysfunctional.
What is monocular blindness?
The loss of sight in one eye due to destruction of the retina or optic nerve.
What results from complete cuts of the optic tract or region V1?
Homonymous hemianopia, blindness of one entire side of the visual field.
What does quadrantanopia refer to?
Destruction of only a part of the visual field due to a partial lesion.
What is a scotoma?
A small blind spot in the visual field caused by small lesions in V1.
True or False: People with brain injuries are usually aware of their scotomas.
False.
What compensatory mechanism allows the visual system to deal with scotomas?
constant movement (nystagmus)
How can it be identified that the type of blindness occurring is due to damage in the optic tract versus the rest of the brain?
If loss of vision affects one eye only, the problem is in that eye or its optic nerve; if it affects both eyes, the problem is likely in the brain.
If vision loss is in one eye only → the issue is in the eye or optic nerve before the optic chiasm.
Each eye has its own optic nerve.
If an optic nerve is damaged before it reaches the brain, vision in that entire eye is lost.
This is because all visual information from that eye is blocked from reaching the brain.
If vision loss affects both eyes → the issue is likely in the brain.
After the optic chiasm, visual information is processed based on visual fields (not individual eyes).
Damage beyond the optic chiasm (in the optic tract, LGN, or visual cortex) will affect the same part of the visual field in both eyes, not just one eye.
A lesion to A would cause?
Central scotoma
Note how only one eye is affected because the lesion is in the eye itself
A lesion to B would cause
Monocular vision loss
A lesion to what area would cause bitemporal hemianopia?
The optic chiasm
Damage to areas D,G and H would cause?
Contralateral homonymous hemianopia
Damage to E and J would cause?
Superior quadrantanopia
Damage to F and I would cause?
Contralateral inferior quadrantanopia
Damage to K would cause?
Contralateral homonymous hemianopia with macular sparing
D.B suffered an angioma on his right V1, upon removal he suffered with blindness in his left eye. This lead him to be unable to identify objects in the blind area but he could tell when an object had blinked and where the source of light was in that area. Why could he do this?
Because his system for processing objects was impaired but the system for locating objects in space was not. So he retained unconscious vision.
He lost the ability to recognize what an object was -> V1 for conscious vision
But he could still detect motion and location because another brain system (the superior colliculus) was still working.
D.Bs case is an example of?
Blindsight
What is achromatopsia?
Complete color deficiency due to a cortical lesion in region V4.
What symptom did L. M. experience after a bilateral lesion in region V5?
Loss of ability to detect movement. So object would vanish when the moved or appear frozen.
The what pathway (ventral) is for—
The how pathway (dorsal) is for—
-What= recognizing what an object is
-How= how to make movements to reach or grasp something
Injury to the What pathway (ventral) leads to what?
Agnosia, not knowing what something is
What 5 deficits can occur due to injury to the what pathway?
1) Visual form agnosia
2) Prosopagnosia
3) Environmental familiarity agnosia
4) Associative agnosia
5) Alexia
What is visual-form agnosia (apperceptive agnosia)?
An inability to recognize objects, real or drawn.
