Visuospatial Processing Flashcards
Higher cognitive functions
IQ, achievement level “fund of information”, abstract reasoning/problem solving/concept formation, social cognition, calculations, sequencing
Hecaen’s Classification of Acalculias
- Alexia and agraphia for numbers
- Spatial acalculia
- Nonspecific (secondary to mem probs, dementia, etc)
- Developmental
- Slowed processing (often with CHI)
- Anarithmetria
3 visual pathways
- retina –> optic nerve (CN2) –> thalamus (LGB/LGN) –> occipital lobe. carries info about color, form, motion, and depth
- retina –> optic nerve –> superior colliculus. Carries info about location of visual stimulus (old pathway)
- retina –> optic nerve –> suprachiasmatic nucleus. Carries information about lightness & darkness.
suprachiasmatic nucleus
nucleus in the hypothalamus; in vision, receives information about lightness and darkness; relates to sleep/wake cycles
V1
primary visual cortex; earliest cortical visual area, AKA striate cortex
specialized for processing info about static and moving objects; excellent in pattern recognition
contains retinotopic map of spatial information, with “cortical magnification” of the fovea
Neurons here have smallest receptive field
with binocular vision, alternating neurons tuned to right and left eyes
Neurons with smaller receptive fields tend to cluster in columns
upper bank of calcarine sulcus responds to lower visual field & vice versa
Line of gennari
(also called the “band” or “stria” of Gennari) is a band of myelinated axons that run parallel to the surface of the cerebral cortex on the banks of the calcarine fissure in the occipital lobe. This formation is visible to the naked eye as a white strip running through the cortical grey matter, and is the reason the primate V1 is also referred to as “striate cortex.” The line of Gennari is due to dense axonal input from the thalamus to layer IV of visual cortex. Although non-primate species have areas that are designated primary visual cortex, some (if not all) lack a stria of Gennari.
V2
Visual association area (1st region within association area)
- receives strong feedforward connections from V1 and sends strong connections to V3, 4, 5
- Cells attuned to orientation, spatial frequency, and color
- 1st area affected by attention
V3 & 3a
Specialized to process FORM
- dorsal V3 is part of dorsal stream (receives input from V1 & 2 and projects to posterior parietal cortex)
- Ventral V3 is part of ventral stream
V4
Part of ventral stream; sensitive to line orientation and color; contains fusiform gyrus; sensitive to attention
V5
(MT) in humans) = posterior middle temporal gyrus at the border of the occipital lobe. Sensitive to motion
Visual pathway for form
retina –> LGN (parvocellular layers) –> V1 (layer 4B) –> BOTH V2 & V3… V2 also projects to V3
Visual pathway for form + color
retina –> LGN (parvocellular layers) –> V1 (layers 2/3) –> BOTH V2 & V4 … V2 also projects to V4
Visual pathway for color
retina –> LGN (parvocellular layers) –> V1 (layers 2/3) –> BOTH V2 and V4 (fusiform gyrus) … V2 also projects to V4
Visual pathway for motion
retina –> LGN (magnocellular layers) –> V1 layer 4b –> BOTH V2 & V5 (MT) … V2 also projects to V5
Motion
V5 and through thick stripes of V2
Color
V4 (& through thin stripes of V2)
Color + Form
V4 (interstripes of V2)
Form
V3 (thick stripes of V2)
Achromatopsia
Lesion to V4 results in loss of color perception, as well as loss of MEMORY of color.
Hemiachromatopsia
Lesion to V4 in only one hemisphere; results in loss of color perception for half of visual field
Chromatopsia
Condition in which ONLY color is perceived; can occur with carbon monoxide poisoning
Akinetopsia (aka motion blindness)
Objects can only be seen when they are at rest; condition results from lesion to V5, which is responsible for perception of movement
Dorsal Stream
“how/where pathway” - - SPATIAL processing; housed in parietal lobes
- location
- movement
- spatial transformations
- spatial relations
Ventral Stream
“what pathway” - - OBJECT processing; only pathway fooled by visual illusions
- color
- texture
- pictorial detail
- shape
- size
parietal lobes
home of dorsal stream
Processes HOW motor acts must be performed (e.g., picking up a pen)
- dorsal stream supports spatial processing of info; projects from primary visual area to parietal regions
- Cells in parietal areas 5 & 7 are sensitive to attributes that allow stable cognitive maps to be made
frontal lobes
dorsal premotor cortex is involved in short-term visuospatial memory (confirmed via lesion studies)
- however, parietal areas are interconnected & active during visuospatial working mem tasks
- visuospatial WM depends on dorsal stream and its connections to frontal lobe
- Guides and plans movements
Temporal lobes
Ventral stream
Hippocampal formation is involved in spatial learning
- we find larger hippocampi in animals who cache (also larger depending on season)
- Damage to hippocampus in rats impairs their ability to learn mazes
- damage results in inability to form new memories of places, produce memories about location
- cells in HC respond preferentially and selectively to spatial locations and form the basis for memories about space
cortical association areas –> entorhinal cortex –> hippocampus (which integrates information)
Binding problem
How do we integrate visual information into a single percept?
- Info from prestriate cortex areas flows to dorsal and ventral streams, carrying different types of information
- connections between adjacent areas and feedback loops facilitate our ability to “bind” visual info
Benton’s Classification of Visual Disturbances
- Visuoperceptual : visual object agnosia, apperceptive agnosia, associative agnosia, prosopagnosia, color anomia
Visual object agnosia
impairment in object recognition in the presence of intact vision, memory, and intellectual function.
- Apperceptive
- Associative
Apperceptive agnosia
Inability to synthesize features into object; may be associated with denial of deficit
good visual acuity, color perception, brightness/contrast discrimination, motion detection
poor shape discrimination
Associated with diffuse brain damage (often carbon monoxide related) and aphasia… it’s been proposed that language may mediate the synthesis of visual info into perceptual objects
Associative agnosia
Disconnection between visual representations and areas of brain responsible for language and memory, or stored visual memories damaged
- perception is spared
- can identify objects by touch or description alone - general object knowledge is intact, but inability to access perceptual knowledge semantically
- NOT just a naming deficit; individuals also cannot pantomime or sort objects by function
- Recognition impairment can occur primarily for
1. objects (with bilateral damage)
2. Faces (with right hemisphere damage)
3. Printed word (with left hemisphere damage)
Prosopagnosia
Inability to recognize familiar faces - often accompanied by recognition difficulty of familiar buildings, landscapes, automobiles.
Are faces special?
- most people with prosopagnosia can also recognize gait, voice, clothing, age, gender, race, and emotional expression.
Identity alone is disturbed.
- SOME people with prosopagnosia can only match unfamiliar faces.
Color Anomia
impairment in which patients can discriminate shades, list the colors of common objects (suggesting intact general color knowledge), but cannot name color in field of vision
- associated with alexia without agraphia
Visuospatial Deficits (according to Benton’s classifications)
- defective localization of points in space (associated with parieto-occipital lesions)
- defective judgment of direction and distance (posterior parietal lesions in RH) - poor depth perception, R-L discrimination, mental rotation, clock hand placement
- Defective topographical orientation (requires RH lesion) - unable to recall memories of spatial layouts, maps. associated with left neglect
- Unilateral visual neglect
Visuoconstructive Deficits (according to Benton’s classifications)
- Defective assembling performance; can be due to damage in either hemisphere. Tested with block design, puzzles & drawings
- Defective graphomotor performance - often due to left parietal damage (angular gyrus) - not apraxia
- copy vs. command may parallel parietal vs. temporal lobe deficits
Visual closure deficits
inability to identify/recognize a symbol or object when only a part of the object is visual
ventral simultagnosia
impaired recognition of the meaning of a whole picture or multiple objects with preserved ability to describe its parts; associated with damage to left inferior temporo-occipital regions
dorsal simultagnosia
Only able to perceive one thing at a time; may bump into things, be unable to localize them. Associated with bilateral parieto-occipital regions
Capgras Syndrome
Sight of loved one results in imposter delusion. may be due to disconnection between visual areas and limbic areas
- vulnerable to reduplication (looking at pics of someone from another angle, a patient can be convinced it is a new person)
Cotard’s
Delusion that one is dead; may be an extreme form of caprgras; may show low galvanic skin responses to everything
Micro & macro somatagnosia
Perception of body part as larger or smaller than it truly is (occurs most commonly with seizures - transient)
Sometimes happens with auras in migraines
Temporal lobes suspected, but not confirmed
autopagnosia
Inability to point to body parts on one’s self (loss of spatial knowledge of one’s own body)
still able to recognize and name body parts
BUT difficulty POINTING to correct body part on command (self or other)
Intact knowledge about the function of body parts, and able to point to clothing items that are associated with certain body parts
finger agnosia
Inability to recognize, identify or name fingers (can also apply to toes). Often accompanied by LR confusion
finger agnosia + LR confusion + dyscalculia + Agraphia = gerstmann syndrome
Gerstmann Syndrome
- Finger agnosia
- LR confusion
- Dyscalculia
- Agraphia
Left-right confusion
occurs most commonly in left-handed women
Body part phantoms
90% of adult amputees experience phantom limbs, but only 10% of children who lose a limb before the age of 6 do.
40% of mastectomy patients report phantoms.
Cause?
Anosagnosia
denial of disorder/deficit (common in individuals with hemiplegia/unilateralneglect)
Common in RH posterior parietal lesion (commonly related to stroke)
- Despite lack of conscious awareness of deficit, will often choose tasks based off deficit (i.e., opting for unimanual task over bimanual one)
Spatial neglect
Failure to report, respond, or attend to stimuli or events in one hemifield (not caused by sensory/motor deficits)
Always on contralesional side
most common with RH damage posterior to central sulcus
Less severe if damage is LH
can test with clock or letter cancellation tasks
usually transient
