Central Vision Processing I Flashcards
vision
- we’re so good at it we take it for granted
- eye is a tiny part of what happens
- not a webcam, it has evolved
- computational task that’s different from who’s integrating it
- high order processing needs integration and analysis
- receptive field gets larger from retina to temporal cortex
- not a measurement of physical properties, takes in the whole picture
- Lady Gaga
coming from the retina
- visual information transduced, processed, and represented:
- faithful spatial representation of visual space/position-retinotopy and receptive field
- intensity, luminance-photons absorbed/transduced by photo-pigments, rods vs cones
- differential spectral absorption- 3 cone types for color
- spatial contrast-center-surround receptive fields, edge detection
- on vs off, positive and negative contrast, sign of contrast, luminance increments and decrements
visual pathways
- retina to LGN to occipital lobe
- nasal retinal fibers with temporal information cross at the chiasm
- left side of visual field to right side of both eyes and then right side of brain (temporal don’t cross, nasal do)
order of layers in the occipital lobe
-contra ipsi ipsi contra ipsi contra
neurons
- optic tract/ radiations neurons still only have information from 1 eye
- doesn’t collaborate until striate cortex
macular sparing
-because 50% of cortex devoted to that small part of the retina
occipital lobe
-fibers from thalamus form layer 4 called the stria
meyers loop
- optic radiation fibers in the temporal lobe (carrying superior visual field and inferior retina information)
- easily damaged
- neurons go synapse on the inferior bank
- parietal radiations are carrying inferior visual field and synapse on the superior bank
perisol cells
- part of the magnocellular (M) pathway
- bigger pathway and more ventral
midget cells
- highest acuity
- part of the parvocellular (P) pathway-which is more dorsal
K pathway
- koneo
- fills in spaces between P and M
- color
P pathway
color,
low luminence contrast,
higher spatial acuity (midget cells),
lower temporal resolution (motion is in M pathway)
M pathway
- perisol cells
- no color
- higher luminance contrast
- lower spatial acuity
- higher temporal resolution
common properties of receptive fields in the retina and LGN
- center surround organization
- mix of cells with on and off center
- retinotopically ordered
LGN cell receptive field
- center surround
- on or off center
- retinotopically specific
- monocular- ipsi or contralaterally driven
- P,M, or K
- maybe color opponent (red/green or blue/yellow)
LGN inputs
- enter V1 and terminate in layer 4
- they make ocular dominance columns
- slab of cells with functionally related areas
- homology to monkeys
neocortex
- has highly conserved laminar architecture with a canonical pattern of wiring of inputs and outputs which cascade from lower to higher cortical areas
- circuitry is the computation
receptive fields of the retina and LGN
- center surround
- off vs on
- on is white on grey
- off is black on grey
orientation tuning
- neurons are orientated to a certain angle and fire more APs at that angle
- neuron still has other receptive field properties, this is just a new one
- this is so we can see the outline of shapes/objects
hubel/wisel serial model for orientation tuning
- each second order neuron has input from many LGN neurons
- LGN neurons line up and second neuron gets stim in orientation from their on centers and likes that angle
order of receptive fields
- retina-V1-V2-V4-temporal
- add more interpretation each time
2 visual processes
- one to extract contours–called form vision
- one to fill in surfaces- color vision
color vision
- red green and blue yellow (red plus green)
- opponent mechanisms
- only see red when you don’t see green
type II color opponent cell- R+ G-
- on with red
- inhibited with green
- responds well to red and poorly to green, yellow, and white
- because white and yellow both have green in them
type I color cells
- spatial opponency
- weak color bias
type II
- chromatic no spatial
- only center part- red on green off
double opponent
- center is one thing and surround is opposite
- chromatic and spatial
cortical columns
- ocular dominance
- orientation
- zebra stripes for orientation
vertical vs oblique electrode
- vertical shows all same orientation
- oblique shows succession of orientations
- cortical circuitry runs vertically across layers
CO blobs
- color tuned
- fill in the space between ocular dominance columns and orientation columns
- retinotopy is also a map
- makes manyyyy big maps so we can see the world better
visual coverage
- one square of the cortex has all the possibilities because it has all the columns
- 2 mm of cortical territory has complete set of columns
extrastriate cortex
split into thick, pale, thin segments
- thick for motion
- pale for form
- thin for color
- lead into this pattern from V1 adds another layer of complexity
- takes what you interpreted from V1 and overlays the layers onto it
visual heirarchy
- complicated
- parietal or temporal pathway
parietal
where
- bilateral lesion leads to deficit in discrimination of landmarks
- draw half the picture
temporal
what
- object discrimination
- bilateral lesions of the temporal lobe leads to a behavior deficit in a task that requires discrimination of objects
