Module 5 Study Guide PDF

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Module 5 Study Guide - Prof. Lleras...

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Important concepts to know – Week 5 The concepts listed below are the most important ones for you to understand in this week. You can use this list to help you with notetaking while you watch the videos.

Module 8 - The Visual System: The Eye 

Definition of light: o Electromagnetic NRG, made up of photons

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Wavelength  Distance b/t peaks o Intensity  Height of the wave o Frequency  # of waves per unit of time Properties of light: o Scattered/diffracted

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 Absorbed

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 Reflected

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 Transmitted

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 Refracted

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Refraction: converging light onto retina, does NOT help bring objects into focus, structures w/ refractive power:  Cornea  Anterior chamber  Posterior chamber Human field of view

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Source emits light, objects in environment REFLECT some wavelengths, this light enters the pupil Cornea and lens focus light onto retina Rods and cones transduce the light into electrochemical signals

o Signal sent to brain by optic nerve Anatomy of the eye (different structures)

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Sclera: protective membrane, white part of eye, only humans have white sclera b/c allows us to know where others are looking Cornea: clear surface that REFRACTS light toward retina Anterior chamber: filled w/ fluid, maintains pressure & shape of cornea Iris: colored part of eye, muscle that opens & closes pupil  Melanin: determines what color the iris is  Heterochromia: 1 person has 2 diff. colored irises (like huskies) Pupil: opening in iris for light to pass thru Lens: adjustable part used for ACCOMODATION, as you age it stiffens, making your near vision suffer (age 40ish) Posterior chamber & vitreous: filled w/ fluids  Floaters: tiny accumulation of proteins/lipids that cast shadow on retina, ***clearer shape when closer to retina, blurrier when farther, fall to bottom of eye due to gravity Tapetum lucidum: structure on back of eye that reflects light back out of the eye to get a second look at it when in low light  red eyes in cat pictures and why a deer in headlights freezes (it’s blinded TWICE by your headlights) Retina: thin layer containing photoreceptor cells (rods & cones) that transduce light into neural signal

  Macula: fovea and area around it (the dark spot in optomap picture)  Fovea: where the image is projected onto Pupillary reflex o An automatic process that expands the pupil in dim light and constricts it in bright light

o Accommodation

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Rapid adjusting of the lens so that both near and far objects can be seen, focuses the light onto the retina  Stretched: far vision  Fat & bubble-y: close vision ***KNOW REFRACTION VS ACCOMODATION!!***

Near point o Closest dist. the eye can focus, becomes farther as you age due to lens stiffening Presbyopia o Light focuses behind retina => hard to focus on close objects  ***this is farsightedness due to aging and lens stiffening Retina:

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What is the fovea?  A dip in the retina where concentration of cones is greatest, this is where light is directed toward  At center of fovea, [ ] of cones is 100%, then gets less and less as you move outward w/ more and more rods  Light gets directed to center when you need to see fine visual detail  Light has to go thru all other retinal layers to reach photoreceptors on other side (in pigment epithelium and choroid) Fovea vs. Periphery:

 Optic disc  No photoreceptor cells are located here, this is where optic nerve leaves the eye  ***this is the bright spot in an optomap

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 All veins lead to this spot  Only have a blind spot here w/ monovision, when you use both eyes, no blindspot Photoreceptors:

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Cones  For color/daytime vision, high visual acuity  3 visual pigments:  S-cones: shorts wavelengths (blue & violet)  M-cones: medium (yellow)  L-cones: long (red) o Rods  For black/white/night vision  Visual pigment: rhodopsin Horizontal cells o Allows cross-talk & lateral inhibition b/t the photoreceptors Bipolar cells: o Receive info from photoreceptors, sends signals to retinal ganglion cells o Midget  1 cone -> 1 bipolar cell  Located in fovea for high visual acuity o Diffuse  50 photoreceptors -> 1 bipolar cell  Pools info across the many photoreceptors => loss of fine visual detail Amacrine cells o Receive info from bipolar cells & other amacrine cells, cross-talk Ganglion cell: o Receive info from bipolar cells, send signal to brain via optic nerve o P-ganglion cells

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 1 cone -> 1 midget bipolar cell -> 1 p-ganglion cell  Fine detail, shape, & color o M-ganglion cells  Many photoreceptors -> 1 diffuse bipolar cell -> 1 m-ganglion cell  Motion & spatial relation Transduction of light: o Photopigment  Molecule that absorbs light & releases electric potential o Opsin  Protein part of photopigment that captures photons and begins process of transduction o Classes of receptors

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Even though the peak for l-cones is far from having a peak sensitivity to red wavelengths, it still has some sensitivity to it Duplex Theory of Vision: o Photopic vision  Cones and color/daytime vision (3 cone types)  Peak sensitivity: ~550 nm  Good acuity o Scotopic vision  Rods and grayscale/nighttime vision (1 rod type)  Peak sensitivity: ~505 nm  Poor acuity Convergence and Acuity o Consequence of pooling across multiple photoreceptors, improves light sensitivity Dark adaptation o Light bleaches the rods, rhodopsin needs time to replenish (why pirates wear eye patches)

o Light adaptation

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o Blinded by sudden flooding of light after being in dark, can take a few minutes to complete Retinal Ganglion Cells: o Receptive field  Area in visual world that a neuron can be stimulated by o On-center ganglion cell  Receptive field of ganglion cells fire like crazy when light is in center of field, but when in surround, firing rate silences

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 Off-center ganglion cell  When in surround, fires like crazy, when in center, silences (opp. of on-center)  (-s and +s should be reversed in off-center picture) Lateral inhibition  Facilitates edge detection (where object starts & stops), caused by inhibitory signals in horizontal cells

Refractive error & diseases of the eye: o Myopia  Nearsightedness, can’t see close, light focuses in front of retina (lens refracts too much)  Far objects are blurry  Fixed by glasses/contacts that DIVERGE light o Hyperopia  Farsightedness, can’t see close, light focuses behind retina (lens refracts not enough)  Close objects are blurry o Astigmatism  Cornea is misshapen => multiple focal points o Cataract  Clouding of the lens, common in older patients  If cloud becomes intense enough, can’t see thru it and go blind o Macular degeneration  Big black spot in center of vision, from UV ray damage to macula (wear sunglasses!) o Retinitis pigmentosa  Affects peripheral vision, creates tunnel vision effect Vision Prostheses o Devices intended to restore visual function

Module 9 - The Visual System: The Brain 

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Work by Wiesel and Hubel o Nobel Prize for work on visual cortex o Certain areas of brain are specifically sensitive to certain stimuli o Found visual system likes specific PATTERNS of light, not dots of light (from cat experiment: responded to movement of edge of slide, not the dot on it) Structures along the visual pathway:

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***half of info from each eye goes to each side of brain An object in left field of vision is processed in right side of brain (contralateral) Temporal retina (near ear side of each eye) = ipsilateral org.n (goes to same side of brain) Nasal retina (near nose side of each eye) = contralateral org.n (goes to opp. side of brain) Optic nerve  Where signals from photoreceptors in eye are sent out to brain Optic chiasm  Crossing of optic nerves from each eye in brain Optic tract  Continuation of optic nerve that relays info from optic chiasm to LGN & superior colliculus

 LGN (learn the 8 properties)  Lots of layers that block or allow visual info into brain  Magnocellular pathway (Layers 1 & 2): get info from m-ganglion cells  Parvocellular pathway (Layers 3-6): get info from p-ganglion cells  Koniocellular pathway (b/t magno & parvo layers): only for blue light

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each LGN receives info from both eyes but only info from the opp. side the LGN is on info is maintained in separate layers Topographic mapping: locations next to each other in real world (and on retina) are processed by neurons next to each other in the brain Optic radiation  Superior Culliculi

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Function  At top of brainstem, controls rapid eye movements  10% of incoming visual info goes here  Saccades  fast eye movement from 1 object to another  Smooth-pursuit eye movements  Voluntary tracking eye movements Visual cortex:

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Layers  V1 has 6 layers o Layer 4: receives info from LGN, has multiple sublayers o more complex cells are in deeper layers (closer to 6th) o less complex are closer to 1st layer Retinotopic map  A point-by-point relation b/t the retina and V1 (#s 1-9)

 Cortical magnification  Allocation of more space in the cortex to some sensory receptors than to others Visual crowding  A very busy background makes it hard to find something

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Look at white circle, it’s harder to find something in the periphery than if it was just a blank background

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Bar Detector

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o Simple cells: o orientation tuning curve

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 End-stopped cells o Prefer certain lengths of bars of light Organization of V1:

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Hypercolumn  Show patterns of cells that prefer diff. orientations  As you move down a column, maintains orientation preference but becomes more complex cells  Blobs: help maintain color info sent from eye to brain

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V2

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o Called the extrastriate cortex, involved in representing the world Funtional pathways:

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Ventral (“what”, parvo) pathway  Goes around and down side of brain  V4: sensitive to binocular disparity, shape recognition, color  Inferotemporal cortex: object recognition  Object agnosia: can detect details of an object but can’t name the object (can’t recognize faces) Dorsal ("where", magno) pathway  Goes up and over top of brain (like “dorsal fin” on top of fish)  ***don’t need to know the object coming at you, just know you have to duck to avoid it  V5: motion & spatial relations  Parietal lobe: visual guidance of reaching and grasping Where does vision come together?  NOWHERE!!! There is no final place where everything comes together  Vision happens b/c of simultaneous activation across all visual areas  It also doesn’t flow in 1 direction, it goes fwd & bwd

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 Development of the visual system: o The Kitten Carousel Experiment  One cat free to move wherever, other just goes opposite to the way the other cat moves o Critical Period: what is it?  Time in adolescence when you must fix visual problems before they become permanent  Brain has highest plasticity during this time o Cataract  Clouding of lens o Strabism  Lazy eye Visual acuity o How small are the details that you can depict o

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Ex: at one point, these lines become a grey square

o ----------- spatial frequency o how many black and white stripes can we fit in a fixed amount of space

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o Development of spatial frequency in children o Low spatial frequency developed by 9 weeks o High spatial frequency not developed until 3-4 years! Selective adaptation: what is it? o Fatigue the neurons by exposing them to a stimulus, when they are fatigued, they respond less and less and your perception will be altered => aftereffect o Tilt aftereffect  Vertical bars seem slightly tilted to left after looking at diagonally right bars

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 ------ Color aftereffect  See an after-image w/ opposite colors

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Blindsight o Unconscious residual visual capacities shown by blind patients o

Ex: blind patients guessed better than chance on happy vs sad faces and much more...