Karteikarten
Chapter 10 - Vision
Karten in diesem Stapel (43)
- 12 categories of eye functionsOptic functions - capture light, form spatial image
Neural functions - transduces light into neural signals & processes signals - 2Parts of eyeCornea - transparent curved outer layer, refracts & focuses light
Iris - opening for pupil
Pupil - controls amount of light entering
Lens - focuses light on retina, flattens/ widens for distances = accommodation, controlled by ciliary muscles
Retina - photoreceptors & neurons
Fovea - center of retina (cones)
Extraocular muscles - control eye movement, 3 pairs - 3Retina picture
- 4Types of receptors in retinaPhotoreceptors - rods & cones
Horizontal cells
Bipolar cells
Amacrine cells
Ganglion cells - axons form optic nerve, 1st cells with APs (others have local graded potentials) - 5Scotopic systemUses rods
Works in dim light
No colour differentiation
Many rods give info to each ganglion cells = lots of convergence - 6Photopic systemUses cones
Requires more light
Has differential sensitivity to wavelength = colour vision
Some ganglion cells get info from only 1 cone = less convergence - 7PhotopigmentsContain 2 parts: Retinal & Opsin
Rods use Rhodopsin
Cones use 3 classes of opsins - 8Regulation of Na channels in photoreceptorsOnly in photoreceptors (normal APs in bipolar cells on)
Light hits rhodopsin -> retinal dissociates to reveal enzyme site -> activates G protein -> closes Na channels -> hyperpolarization -> activates visual pathway
- 9Range of intensities dealt with by:Adjusting pupil size - controlled by special ganglion cells with own photopigment
Range fractionation - different receptors handle different intensities - ex. rods = low threshold, cones = high
Photoreceptor adaptation - adjusts sensitivity to ambient light by changing [Ca] - 10Visual fieldArea you can see without moving head or eyes
Visual acuity best in center
Fovea = highest acuity (most cones)
Optic disc = blind spot (blood vessels & where gangion axons leave - no receptors) - 11Location in world & how it crosses over
- 12Visual pathwaysMajor targets of retinal ganglion cells
Lateral geniculate = vision
Superior colliculus = coordinates & detects movements
Suprachiasmatic nucleus = Circadian clock
Pretectum = pupil & lens reflexes - 13Types of retinal ganglion cellsM cells (magnocellular) - inner 2 layers, large, get input from rods, all over retina, very sensitive, colour blind
P cells (parvocellular) - outer 4 layers, small, get input from cones, mostly in fovea, colour sensitive & perceive fine detail - 14Lateral geniculateGets input from P pathway (outer 4 layers) & some of M (inner 2) pathway
Each layer get input from only 1 eye
(1,4,6 = contralateral, 2,3,5 = ipsilateral)
Sends output to V1 (striate cortex)
Each cell has receptive field - sum of RFs of all ganglion cells inputting to LGN cell - 15Superior colliculusIn tectum
Input from some M pathway
Sends output to thalamus + parietal & temporal cortices
Analyzes & coordinates movements (blindsight) - 16Coding location in cortexGet input from multiple LGN cells
Fovea disproportionally represented
Visual world flipped around (top = ventral)
- 17Spatial-frequency filter modelSpatial freq = # of dark-light cycles/degree of visual space
Uses Fourier analysis (sine waves) vs. patterns of bars - 18Visual cortexV1 = primary visual cortex/striate cortex
V2, 3A, 3B, 4 & 5 - extrastriate/secondary visual cortex
V1 = perceives objects/events & forms mental images
V2 = responds to illusory contours
V4 = gets input from V2, together: perception of form
V5/medial temporal = motion perception
Inferior temporal = moderately complex shapes, shaped by learning - 19Geniculostriate systemLGN -> layer 4 of V1
L/R segregation preserved
Ocular dominance columns - 20Receptive fieldsGanglion cells get input from many photoreceptors - can be inhibitory or excitatory
Receptive fields = center/surround
Response depends on where in field it's stimulated
Light -> hyperpolarization (less glutamate) - 21Ganglion cellsDon't see shapes
Very small dots as receptive fields
Respond to presence/absence of light
Center/surround
Have overlapping fields - 1 photoreceptor contributes to many RFs (can be on & off) - 22Detection of edgesUses activity of adjacent receptive fields - those near edge = largest change in response (brain overemphasizes)
- 23Lateral inhibitionInterconnected neurons inhibit neighbours - produces contrast at edges of regions
Inhibition via own axons/interneurons - 24Orientation columnsHorizontally adjacent cells respond to similar stimuli
Vertically adjacent cells respond to identical stimuli - 25Segregation of function in V1Cortical columns - cells in layer respond to same stimuli
Blobs - cell clusters responding to colour
Interblobs - clusters of cells responding to form & motion (between blobs) - 26Segregation of function in V2Segregation preserved from V1 to V2
Thin stripes = colour / Thick stripes = motion / Pale zones = form
Revealed by stain via metabolic activity - 27Examples of cortical columnsOcular dominance columns - vertical, responds more/less to stimulation in 1 eye
Orientation column - responds to stimuli of certain orientation - 28Flow of info in brain
- 29V1 cellsLarger RFs
More complex responses
Respond best to bars of certain orientation
On-off arrangement
SIMPLE - orientation detectors, respond best to certain width, orientation & location in VF - input from LGN cells
COMPLEX - respond to certain size & orientation anywhere in VF, also in V2 & V3 - input from simple cortical cells
HYPERCOMPLEX - like complex but with excitatory & inhibitory parts of VF - 30How are visual fields connected?Corpus callosum fuses medial part of visual field
- 31V2 functionsSimilar responses as V1
+ higher order integration & responds to illusory contours - 32V3 (basics only)V3A = dorsal stream - gets input from V1 & V2 & projects to posterior parietal - for global motion & form
V3B = ventral stream - strong connections with inferior temporal & weak with V1 - for colour & dynamic form - 33Ventral vs. Dorsal streamsVentral = identification of object = what - esp involves visual cortex
Dorsal = location of object = where - esp involves superior colliculus
Connections between
Includes mirror neurons (mainly dorsal) - 34Optic ataxiaDamage to dorsal stream
Trouble using vision to reach for/grasp objects but can still ID them - 35V4 & V5V4 = colour - responds to different sinusoidal spatial frequencies/geometric shapes - responds best to complex stimuli
V5 - responses best to motion (damage = grasping problems) - 36Temporal lobe functionsVisual association cortex
Gets input from visual cortex via ventral stream
Most excited by complex visual stimuli
Arranged in columns - each responds to lightly different forms of object
Can be modified by experience - 37Other extrastriate cortex areasInferior temporal lobe - specific complex forms
Fusiform gyrus - faces (damage = prosopagnosia)
Prefrontal cortex - facial processing, input from inferior temporal gyrus & superior sulcus - 38Types of colour visionExcellent trichromatic - 3 cones (us)
Robust dichromatic - 2 cones (dogs)
Feeble dichromatic - 2 cones but few in numbers (cats)
Minimal colour vision - single cone (raccoons) - 39Trichromatic theoryColour comes from combining differential activation of different cones
Colours made by mixing red, green & blue
Each is labeled line to brain
Colour determined by ratio of activation
Full activation of all = white light - 40Opponent process theoryColours perceived in balanced pairs: Red/Green, Blue/Yellow & Black/White
Colour balance occurs at ganglion cell level via center-surround arrangment
Short wavelength cones = blue, Medium = green & yellow, Long = red & yellow - 41Opponent process vs. trichromatic in colour visionBoth play role
Trichromatic = how photoreceptors work
Opponent process = how colour is handled through rest of CNS (after photoreceptors) - 42Where & how colour constancy is producedIn V4
Different wavelengths can be perceived as same colour
Same wavelength can be seen as different colour
How objects maintain colour with lighting changes - 43Visual deficienciesMyopia = nearsightedness - retina too long
Amblyopia = poor acuity in 1 eye even with normal eye/retina
Macular degeneration = progressive vision loss due to photoreceptor death
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- Final stuff (P375) Karteikarten am Chapter 10 - Vision, erstellt von Megan Willerth am 20/11/2014.
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- Megan Willerth
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