6/3- Higher Cortical Function Flashcards
What is sensation (def)?
Detecting a stimulus e.g. photoreceptor capturing photon
What is perception (def)?
Understanding the stimulus; construction of the brain (requires higher cortical function)
Examples of how perception differs from visual sensation?
- Gradients
- Moving sticks
- Subjective contours
Examples of higher cortical function processes (pt cases)?
- Can only see 1 thing at a time; cannot perceive 2 objects simultaneously
- Deaf man loses ability to sign with his fingers, even though his muscles are fine
- Paralyzed but completely denies it
- Can copy a drawing but cannot name what it is
- Can understand language but has lost the ability to read or write
What makes a cortex area “primary”?
Input mainly from thalamic relay nuclei e.g. striate cortex receives input from LGN
What makes a cortex area “secondary”?
Input mainly from primary cortex within the sensory system
What makes a cortex area “tertiary” (or higher- association cortex)
Input from 1+ sensory system, usually from 2ndary sensory cortex
3 principles guiding the interactions of sensory cortex?
- Hierarchical organization (specificity and complexity increases with each level)
- Functional segregation (some groups care about color, edges, angles, movement…)
- Parallel processing
Damage results in difference due to hierarchical organization. What happens when you damage receptors?
Complete loss of ability to perceive in that modality
(e.g. deafness, blindness)
Damage results in difference due to hierarchical organization. What happens when you damage ‘higher’ areas?
Complex and specific deficits
(e.g. man who mistook his wife for a hat)
Where are the primary, secondary, and tertiary cortices located for vision?
Primary (V1)- posterior occipital lobe
Secondary (V2):
- Prestriate cortex- a band of tissue surrounding V1
- Inferotemporal cortex
Tertiary (V3)- various areas, largest single area is in posterior parietal cortex
What is a scotoma?
Area of bindness resulting from damage to V1
- Blind in corresponding contralateral visual field of both eyes
- Deficit may not be readily detected due to phenomenon of completion (ex of physiological scotoma (although not from V1 damage) everyone filling in background over area of optic disc)
What results from damage to secondary visual cortex?
Visual agnosias- failure of recognition
- Visual agnosia: visual capacities intact, but unable to recognize (recall man who mistook wife for hat); many subtypes (object, motion/akinetopsia, color/acrhomatopsia)
- These result from damage to specific areas of 2ndary visual cortex
2 examples of visual agnosias (broad types)?
Associative agnosia- cannot associate visually-presented objects with their semantic meaning, or organize objects into semantic categories
Apperceptive agnosia- fail tests such as visual matching, comparing similar figures and copying drawings
These match to the dorsal and ventral streams
What is the dorsal stream in charge of? Where does it go?
- “Where”/control of behavior
- V1 to dorsal; V2 to posterior parietal
What is the ventral stream in charge of? Where does it go?
- “What”/conscious perception
- V1 to ventral; V2 to inferotemporal cortex
Where is the lesion in a pt who can’t see objects but can grasp them correctly (can’t tell you orientation, but can interact to put something in slot just fine)
Ventral stream
Where is the lesion in a pt who can see but cannot grasp correctly?
Dorsal stream
What is hemi-neglect?
Aka “hemi-attention”
- Neglect most often occurs following damage to the R parietal
- Pts behave as though one half of the world does not exist, but are completely unaware of the missing half; they do not miss it
- Only dress/shave one side, only eat half dinner, bump into doors, ignore/transpose sounds and sights from left side, reading errors
- NOT caused by a visual deficit (can still see something scary in other hemisphere)
(- Pt can see perfectly fine, but left half of visual field is ignored)
TESTS: only draw half of a picture, 12 digits of clock all put on right side, deviated midline when told to bisect, read only words on the right side, copy only right side of a picture
What causes Balint’s syndrome?
Bilateral damage to the posterior parietal lobes (as opposed to just R damage as in hemi-neglect); damage to dorsal stream
What is Balint’s syndrome? Examples?
Can’t see visual field as a whole
What is simultanagnosia?
Inability to see visual field as a whole (result of Balint’s?)
- Difficulty in copying/drawing/writing because they are unable to see both the end of the pen and what is on the paper at the same time
- Unable to describe complex scene
- Test with overlapped drawings
Where does the ventral stream run?
Damage to the path causes what deficits?
Occipito-temporal
- Visual object agnosias (e.g. prosopagnosia)
- Achromatopsia (loss of color vision)
Where does the dorsal stream run?
Damage to the path causes what deficits?
Occipito-parietal
- Apraxia
- Optic ataxia (deficit in reaching under visual guidance)
- Akinetopsia (motion blindness)
- Disorders of spatial cognition (hemi-neglect, Balint’s, simultagnosia)
What is the input for SII?
Organization?
uni or bilateral?
- Mainly input from S1
- Somatotopic
- Input from both sides of body
What does the primary auditory cortex sense? Secondary? Tertiary?
Primary: pure tones
Secondary: respond to more complex stimuli such as monkey calls (do not respond well to pure tones)
Tertiary: language comprehension
