Lecture 7: Occipital Lobes Flashcards
Striate Cortex
the primary visual cortex (area 17, VI) in the occipital lobe
has a striped appearance when strained
Dorsal Stream
a visual processing pathway from the primary visual cortex to the parietal lobes
guides movements relative to objects
Ventral Stream
a visual processing pathway from the primary visual cortex to the temporal cortex for object identification and perception of related movements
Dynamic Form
the shape of objects in motion
Egocentric Space
a spatial location relative to an individual’s perspective
Allocentric Space
object location relative to another object, independent of the observer’s perspective and usually at a distance
Polysensory Neurons
a neuron within multimodal cortex that is responsive to both visual and auditory or both visual and somatosensory input
Bitemporal Hemianopia
loss of vision in both temporal fields due to damage to the medial region of the optic chiasm that serves the crossing fibers
Homonymous Hemianopia
blindness of an entire visual field due to complete cuts of the optic tract, lactal geniculate body, or area 17 (VI)
Macular Sparing
a condition that occurs only after unilateral lesions to the visual cortex in which the central region of the visual field is not lost, even though temporal or nasal visual fields are lost
Quadrantanopia
defective vision or blindness in one-fourth of the fovea (visual field)
Scotomas
a small blind spot in the visual field caused by small lesions, an epileptic focus, or migraines of the occipital lobe
Infarct
an area of dead or dying tissue resulting from an obstruction of the blood vessels that normally supply the area
Blindsight
the ability of patients with visual-field defects to identify at better-than-chance levels the nature of visual stimuli that are not consciously perceived
Ischemia
deficient blood flow to the brain due to functional constriction or actual obstruction of a blood vessel by a clot
Angioma
collections of abnormal blood vessels, including capillary, venous, and arteriovenous malformations, that result in abnormal blood flow
Visual Agnosia
an impairment in the recognition of visually presented objects that is not a result of a deficit in visual acuity or language
Optic Ataxia
a deficit in visually guided hand movements that cannot be ascribed to motor, somatosensory, or visual field or visual-acuity deficits
Propagnosia
a facial-recognition deficit not explained by defective acuity or reduced consciousness or alertness
rare in pure form and thought to be secondary to right parietal lesions or bilateral lesions
Alexia
inability to read
Apperceptive Agnosia
a broad category of visual agnosias in which elementary sensory functions appear intact but a perceptual deficit prevents object recognition
Simultagnosia
an agnosia symptom in which a person is unable to perceive more than one object at a time
Associative Agnosia
inability to recognize or identify an object, despite its apparent perception
Topographic Disorientation
following brain injury, a gross disability in finding one’s way in relation to salient environment cues
likely due to topographic agnosia and amnesia
What is the medial surface of the occipital lobe?
parieto-occipital sulcus
calcarine sulcus/fissure: contains much of primary visual cortex, separates upper and lower visual fields
What is the ventral surface of the occipital lobe?
lingual and fusiform gyrus
V2, VP, V4
What are the connections to the primary visual cortex (V1)?
input from LGN (lateral geniculate nucleus)
output to all other levels
What are the connections to the secondary visual cortex (V2)?
output to all other levels
What are the connections in the visual cortex after V2?
output to the parietal lobe - dorsal stream
output to the inferior temporal lobe - ventral stream
output to the superior temporal sulcus (STS) - STS stream
What is the dorsal stream visual pathway?
visual guidance of movements
“where” things are in space
What is the ventral stream visual pathway?
object perception
What is the STS visual pathway?
visuospatial functions
movement perception (e.g., biological motion)
What is the dorsal stream test in double dissociation?
researcher puts food in one of the drawers, use cylinder to show where food is, location information
dorsal stream damage: have problems with “where” task, perform at chance levels, no issues with “what” task
What is the ventral stream test in double dissociation?
food is determined by shape on top of drawer, monkey needs to differentiate between shapes
ventral stream damage: cannot recognize objects, perform at chance levels, “where” task is unaffected
What is the responsiveness of cells in the ventral visual stream?
as you progress down the ventral stream, the complexity of neurons increases because the object processing becomes more complex
increase in complexity as you move forward
shows functional specificity
What is color vision?
primary job of V4, but distributed throughout occipital cortex
plays a role in detection of movement, depth, and position
What are the visual functions beyond occipital lobe?
vision-related areas in brain make up about 55% of total cortex surface area
multiple visual regions in temporal, parietal, & frontal lobes
vision is not unitary: composed of many quite specific forms of processing, five categories for vision
What is the lateral occipital cortex?
perceptual constancy for: size, location, viewpoint, illumination
form-cue invariance: photos, real objects, line drawings
What is the Goodale & Milner model of vision for perception and vision for action?
dorsal stream feed into parietal where things are, plan motion to get to object
What are the categories of vision for action?
parietal visual areas (dorsal stream)
reaching
ducking
catching
What are the categories of action for vision?
visual scanning
eye movements and selective attention
What are the hemisphere differences in how the brain processes faces?
look at left side more in mirror, but right side more in photos
right hemisphere dominance for face processes causes bias in eye movement so info gets to right hemisphere faster
more attention in left visual field
What is visual recognition?
temporal lobes
object recognition
ventral stream
What is visual space?
parietal and temporal lobes
spatial location
STS stream
What is visual attention?
selective attention for specific visual input
parietal lobes guides movements and temporal lobes help in object recognition (independent attentional mechanisms)
What are disorders of visual pathways?
monocular blindness
bitemporal hemianopia: results from lesion to medial region of optic chiasm
nasal hemianopia: results from lesions of lateral region of optic chiasm
What is the optic chiasm?
LVF to right side of both retinas (one nasal and one temporal)
nasal hemiretina information crosses at optic chiasm
temporal hemiretina information stays ipsilateral
for a given VF: information from one eye crosses the optic chiasm, information from the other eye says ipsilateral
once past the optic chiasm full VF information together in contralateral hemisphere
What are field defects in vision?
scotomas: smaller portion of a quadrant is missing
often go unnoticed due to nystagmus
What are the symptoms of V1 damage and scotoma?
right infarct (dead tissue) in occipital lobe
experienced blindsight - perceive motion and location without perceiving content
lost one-quarter of fovea, poor vision in upper left quadrant
slow facial recognition
What are the symptoms of V1 damage and blindsight?
angioma in right calcarine fissure
hemianopia
cortical blindness - blindsight - reports no conscious awareness of seeing, but can report movement & location of objects
accurate pointing to light source locations
What are the symptoms of V4 damage and loss of color vision?
sustained concussion and suddenly lost color vision
closes eyes to eat - dreams
specific damage in occipital cortex
improved acuity at twilight or at night
years later, no longer remembered color
What was the case of conscious color perception in a blind patient?
ischemia destroyed large area of posterior cortex - electrocuted
can only detect presence or absence of light and has intact color vision
could identify and name colors, also name typical colors for objects from memory
What is the case of V5 (MT) damage and the perception of movement?
vascular abnormality produced bilateral posterior damage
loss of movement vision - people appeared “here or there”
unable to intercept moving objects by using hand
TMS to V5 in NI led to inability to intercept
V5 (MT) likely involved in both perception and action
What is the case of parietal damage?
bilateral hemorrhages in occipitoparietal regions
disordered control of gaze, impaired visual attention, and optic ataxia (deficit in visually guided hand movement)
can recognize and name objects, but cannot accurately reach for objects
What is the case of occipital damage and visual agnosia?
bilateral damage to lateral occipital cortical region and tissue between parietal and occipital lobes
visual form agnosia - inability to recognize line drawings of objects
can use visual information to guide movements, but not to recognize objects
What is apperceptive agnosia?
perceptual categorization
cannot form a percept of whole
can recognize local aspects
What is the associative agnosia?
cannot link percept to knowledge
What is category specific agnosia?
know all objects except those linked to a specific category e.g. fruits
memory access disorder
What is the system of face processing in monkeys?
specific features in IT
What is the system of face processing in humans?
posterior right hemisphere
configurational info
inversion effect (larger for faces than houses)
What were the results of multi-unit cell recording and face recognition?
patient was awake, recording from FFA, look for activation
specificity for face, and for a specific type of face
What is the role of experience in recognition?
show radiologist a set of x-rays, then ask have you seen this before
all groups do well on faces
senior radiologists are better able to recognize if they’ve seen the image before
they do worse when there is nothing abnormal in the x-rays because they are trained to detect abnormal
FFA gets recruited to process things other than faces
What is covert face recognition?
name reading task
intact –> longer reaction time for mismatched condition
prosopagnosia –> perform the same as the intact on the mismatched task influences their reaction time, some unconscious awareness that they still know something about the face
