9.5 and 9.6 Flashcards
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.
What condition did D. F. suffer from after CO poisoning?
Extensive lesion of the lateral occipital region, lead to visual-form agnosia.
What ability did D. F. retain despite her visual-form agnosia?
The ability to appropriately shape her hand when reaching for objects.
So she could still use her how pathway to understand the structural features of an object and grab it correctly
Visual form agnosia is often accompanied by what?
Simultagnosia- When you cannot see more then one thing at a time
What is associative agnosia?
Perceives objects but cannot identify them. No meaning.
Ex. Would copy an object but not know what it is
The patient can copy a drawing but cannot tell you what it is, this is a case of?
Associative agnosia
Damage to the FFA leads to?
Prosopagnosia (facial agnosia), they cannot identify faces
Someone returns to the town they grew up in and is unaware this is their home, they are suffering — which is cause by damage to —
Environmental familiarity agnosia, damage to their FPA
What is alexia and what is it caused by?
Damage to the left fusiform and lingual gyrus causing an inability to read
The How pathway (Dorsal)is involved in?
Movement/Action
What syndrome did R. Bálint describe related to parietal lesions?
Optic ataxia.
What is the primary deficit in patients with optic ataxia?
Severe deficit in visually guided reaching despite normal object recognition.
What is the deficit characterized by an inability to perform meaningful coordinated movements?
Ideomotor apraxia
What distinguishes dorsal stream damage from ventral stream damage?
Dorsal stream damage affects movement guidance while ventral stream damage affects object perception.
Fill in the blank: D. F.’s lesion interfered with her _______ pathway.
ventral
Fill in the blank: R. V. could recognize objects but could not guide her hand to _______.
reach for objects
How do patients with dorsal stream damage perceive objects?
They can see perfectly well but cannot accurately guide movements based on visual information.
How do patients with ventral stream damage guide their movements?
They can guide movements based on visual information despite not being able to perceive objects.
9.6 What did the pioneering work of Torsten Wiesel and David Hubel (1965) demonstrate about visual deprivation in kittens?
Depriving one eye of visual information led to shrinkage of cortical areas for the deprived eye and poor vision (amblyopia), while expanding cortical areas for the non-deprived eye.
What is amblyopia?
A condition resulting in poor vision in one eye due to visual deprivation.
What was the outcome of fitting kittens with goggles that only allow vision of lines of a single orientation?
Deficits in perceiving lines of other orientations.
How can injury to the occipital cortex affect visual perception?
It can cause severe visual impairments initially, but significant recovery can occur as the brain adapts over time.
What did Shibuki et al. (2020) find regarding rehabilitation after occipital cortex injury?
Individuals often respond well to rehabilitation even when it is initiated long after the injury.
What was unique about B. I.’s case as described by Inaki-Carril Mundinano and colleagues (2019)?
Despite extensive occipital lobe damage early in life, B. I. had good conscious visual abilities, recognizing facial expressions and colors.
What did MRI tractography reveal about B. I.’s visual pathways?
An expanded pulvinar–V5 pathway and LGN–V5 pathway likely supported his visual abilities.
What is echolocation?
The ability to perceive objects by the sound reflecting from them.
What did Liam Norman and Lore Thaler (2019) discover about blind echolocators?
MRI identified active regions in the occipital cortex during echolocation, suggesting spatial maps from auditory inputs.
What role does experience play in the development of the visual system?
Experience helps neurons improve their selectivity to identify novel objects, enhancing visual abilities.
What was the outcome of Tanaka’s work (1993) on shape processing in the ventral stream of monkeys?
Trained monkeys showed 39% of TE neurons responded maximally to specific stimuli, compared to 9% in untrained animals.
True or False: Our visual abilities are solely genetically determined.
False
Fill in the blank: The changes in visual abilities are significantly modified by _______.
experience
