Class_03_Perception, and Visuospatial Processing and Action Flashcards
How Pathway
Where pathway
Dorsal pathway
V1 -> Parietal lobe
What Pathway
Ventral pathway
V1 -> Lateral Occipital complex (LO) -> Temporal lobe
Blood Supply for Both Pathways
Posterior cerebral artery (PCA)
Damage to Ventral Pathway
Problems with recognition
Damage to Dorsal Pathway
Problems with using vision for action
Agnosia
Without knowledge
- Inability to recognize things from sight
2 Forms of Agnosia
- Apperceptive agnosia
- Associative agnosia
Apperceptive Agnosia
Failure in recognition
- due to deficits in the early stages of perceptual processing
- with intact sensation of light
- is not blind
- cannot form the perceptions that they used to before brain damage
- color, motion and form
- cannot copy drawings
Associative Agnosia
Failure in recognition
- unimpaired perceptual processes
- a problem with linking perception to existing knowledge
Stages of Visual Perception by Lissauer (1890)
- Conscious awareness of a sensory impression
- processing of things like color, motion and form - Visual percepts are connected to knowledge that we have
- to memories
Types of Apperceptive Agnosia
- Cerebral achromatopsia
- Akinetopsia
- Visual form agnosia
- Visual texture agnosia
- Integrative agnosia
- Hemiagnosia
Visual Form Agnosia
could not recognize objects by sight
- could not copy simple line drawings
- rare
Cause of Visual Form Agnosia
- Carbon monoxide poisoning
-> damages temporal lobes - a heart attack
-> damages occipital lobes
Test of Perceptual Problem in Representing Form
- Efron shapes task
- whether pairs of shapes are the same or different - Birmingham Object Recognition Battery – BORB
- Silhouettes of animals
One problem with interpreting tests of basic visual perception
Cannot really be sure why patients are failing
- recognizing common objects, or judging line lengths
- “blinked his eyes everything would come clear”
- scotomata across visual fields
Scotomata across Visual Fields
- ‘blind spots’ may have prevented him from identifying contours of objects.
- couldn’t see his scotomata
- very common in visual form agnosia
- occipital lobe damage
- bilateral visual form agnosia
- simply have low quality vision, not necessarily impaired form perception
Case D.F.
Lateral Occipital Complex Damage
- Lack of oxygen associated with carbon monoxide exposure
- basic form perception
Texture Agnosia
Visual agnosia for textures
- Ventral pathway damage
- a different part of the ventral pathway than object form
Integrative agnosia
Problems with integrating parts of objects into whole percepts
- unable to classify drawings of real and unreal objects
- Wide spread ventral visual pathway damages
Case HJA
- Widespread damage to his ventral visual pathways caused by a stroke
- identify objects by touch
- not by vision
- could make good quality copies of pictures
- could not name what he had drawn
- could not gesture the use of objects that he could not name
- “failing to integrate the two things he saw into a single object within his perception”
Ipsilesional
something on the SAME side of the body as the brain lesion
Contralesional
something on the OPPOSITE side of the body as the brain lesion
Objects in the right visual field are processed in…
contralateral hemisphere, i.e. the left hemisphere
Objects in the left visual field are processed in…
contralateral hemisphere, i.e. the right hemisphere
Lateral Occipital Complex
Visual object recognition
- can’t recognize shapes by form
- can recognize texture
Hemiagnosia
lesions in ventral pathways
- impaired at recognition of shapes and objects presented CONTRALESIONALLY
Associative agnosia
- can perceive normally
- cannot recognize what they see
- cannot associate the perceptions with knowledge of what they are seeing
- copy images well
- not able to name what they had drawn
- can draw objects from memory
- indicating that they had access to the meaning and visual structure of objects
If a patient can see but cannot copy this may indicate…
Apperceptive agnosia
- visual form agnosia
If a patient can copy, this may indicate…
Associative agnosia
- because we assume that they must be able to perceive to be able to copy
- Integrative agnosia, can still copy shapes
Cognitive Model of Object Recognition
- Perceptual Processes
-> Apperceptive agnosia - Association Processes
-> Associative agnosia
2 Causes of Associative Agnosia
- Impaired access to stored knowledge of the shapes of objects
- Disconnection of that knowledge from semantics
Associative Agnosia: Loss of Stored Structural Knowledge of Shape
Right occipito-temporal damage
- stroke in the posterior cerebral artery
- good basic visual sense
- inability to recognize objects from vision
- can copy drawings but can’t name them
- poor drawings from memory
- can’t distinguishing real from unreal objects
- knowledge of visual shape is impaired
Associative Agnosia: Loss of Access to Semantics
- cannot name objects from vision
- good basic perception
- good stores of structure of object shapes
- good knowledge of structural representations of objects (real/unreal)
- can determine objects’ size
- can perform semantic tasks, such as orally describe objects
- disconnection between stored structural knowledge of the shapes of objects and semantic information
