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?
- 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
- 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)
Where is the lesion in a pt who can see but cannot grasp correctly?
What is the inferotemporal cortex?
Final destination (?) cortex of the ventral "what" pathway
- Higher areas in inferotemporal cortex are specific to faces, bodies, animals, houses, tools, etc.
- Moving up the pathway: features -> feature conjunctions -> objects
What does each level of the visual pathway process/recognize?
Anterior inferotemporal: objects, categories
Posterior inferotemporal: complex forms
V4: complex geometric shapes
V2: figures, contours
LGN: luminance, contrast...
Retina: luminance, contrast
What is prosopagnosia?
Inability to recognize faces (face blindness)
Is prosopagnosia a problem with the ventral or dorsal stream? Where is the lesion?
- Problem with the ventral stream
- Lesion in inferotemporal lobe (bilateral damage to the face area in the ventral what/conscious perception stream)
T/F: in prosopagnosia, unconscious face recognition is no longer possible
Dorsal stream is still intact; large skin conductance responses to familiar vs. unfamiliar faces has proved that unconscious face recognition is still possible
What is apraxia?
Deficit in executing or carrying out learned purposeful movements, despite desire and physical ability
Is apraxia a problem with the ventral or dorsal stream?
- Problem with the dorsal stream
Broader damage to dorsal stream can lead to what?
Problems with attention; we have the illusion that we pay attention to everything but we can't
(e.g. Where's Waldo picture)
(e.g. flashing changing pictures)
What is the purpose of selective attention?
Improves perception of what is attended to and interferes with that which is not.
Selective attention acts as a controller to increase the efficiency of all the basic sensorimotor systems
What are the two types of attentive processes? Both are ___?
- Internal cognitive processes (endogenous attention)
- External events (exogenous attention) focus attention
Both of these are spatial
What is hemi-neglect?
- 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
Can attentional systems be broken?
Yes; damage to the dorsal stream (involved with localizing objects in space) e.g. damage to parietal lobe
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?
- Visual object agnosias (e.g. prosopagnosia)
- Achromatopsia (loss of color vision)
Where does the dorsal stream run?
Damage to the path causes what deficits?
- Optic ataxia (deficit in reaching under visual guidance)
- Akinetopsia (motion blindness)
- Disorders of spatial cognition (hemi-neglect, Balint's, simultagnosia)
Where is the primary somatosensory cortex?
Is input uni or bilateral?
- Postcentral gyrus
- Somatotopic organization
- Input is largely contralateral
What determines sensitivity?
Amount of somatosensory cortex devoted to it
What is the input for SII?
uni or bilateral?
- Mainly input from S1
- Input from both sides of body
Where does output from SI and SII go?
Association cortex in posterior parietal lobe
What is astereognosia?
Inabiilty to recognize objects by touch
What is asomatognosia?
Failure to recognize parts of one's own body
e.g. man who tries to throw his own leg out of the bed because he thinks it's not his
What often accompanies asomatognosia?
Anosagnosia- failure of the pt to recognize his symptoms
(e.g. not recognizing that he was paralyzed)
Pathway of sound input?
- Oval window
- Fluid of cochlea
- Auditory nerve axons
- Ipsilateral cochlear nucleus
- Superior olives
- Inferior colliculi
- Medial geniculate nucleus
- Primary auditory cortex
How is the auditory cortex organized?
- Functional columns (cells of a columm respond to the same frequency)
- Tonotopic organization
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