ch. 5: vision/agnosia Flashcards
What is the primary function of the dorsal visual stream?
Spatial location and movement coordination
What is the dorsal visual stream responsible for?
- Spatial location and movement coordination
- Cognitive map for topographical orientation
- Planning and coordination of movement
What are common deficits associated with dorsal stream damage?
- Neglect syndromes (e.g., left neglect)
- Apraxia
- Left-right discrimination problems
- Poor coordination of movement in space
What happens with a right dorsal stream deficit?
Left neglect: difficulty paying attention to stimuli in the left visual field
What happens with a left dorsal stream deficit?
- Rarely results in neglect
- Generally able to attend to both left and right visual fields
What is the ventral visual stream responsible for?
- Object recognition
- Matching visual shapes to internal representations
- Processing colors and faces
What are common deficits associated with ventral stream damage?
- Visual agnosia (inability to recognize objects by sight)
- V4 damage: impaired color perception
- FFA (fusiform face area) damage: impaired face recognition
- Inferior temporal lobe damage: issues recognizing objects and colors
What is agnosia?
Failure to recognize previously familiar stimuli (e.g., visual, auditory, tactile)
What are examples of agnosia?
- Prosopagnosia
- Auditory agnosia
- Phonagnosia
- Tactile agnosia
- Simultanagnosia
Prosopagnosia
inability to recognize familiar faces
Auditory agnosia
inability to recognize common sounds
Phonagnosia
inability to recognize familiar voices
Tactile agnosia
inability to recognize objects by touch
Simultanagnosia
inability to perceive multiple objects at once
What are the two types of agnosia in Lissauer’s stage model?
apperceptive and associative agnosia
Apperceptive agnosia
early-stage perceptual disturbance, inability to copy objects
Associative agnosia
more advanced processing issue, can copy but not recognize objects
What are possible explanations for agnosia?
- Failure of perception to contact memory
- Failure of perception to contact language (visual-verbal disconnection)
- Impairment/degradation of stored representation
- Sensory-perceptual impairment
What is prosopagnosia?
Inability to identify familiar faces using facial features alone
What conditions may coexist with prosopagnosia?
- Object agnosia
- Visual memory loss
- Superior visual field defects (e.g., superior quadrantanopia)
- Achromatopsia (inability to perceive colors)
- Topographical agnosia (difficulty recognizing or navigating familiar environments)
What are the lesion sites for prosopagnosia?
- Bilateral occipitotemporal lesions: more severe deficits
- Unilateral right occipitotemporal lesion: less severe but still impacts face recognition
What abilities are typically spared in prosopagnosia?
- Discriminating age and gender
- Recognizing emotions
- Identifying faces as faces
- Matching faces
- Showing indirect knowledge about faces
What abilities are impaired in prosopagnosia?
- Identifying individuals by facial features
- Describing the owner of a face (semantic knowledge)
- Feeling familiarity when seeing a face
Is prosopagnosia face-specific?
- Deficit is strongest for faces
- May extend to other objects if expertise is required (e.g., greebles in Galthier’s experiment)
What deficits are associated with dorsal stream damage?
- Poor angular judgments
- Poor coordination of movement in space
- Visuoconstructional deficits
- Unilateral neglect
- Topographic disorientation
What is topographical agnosia?
Inability to recognize or navigate familiar spatial environments
What is the ventral visual processing stream also known as?
The “what” stream, responsible for object identification
