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CLEMSON / Psychology / PSYC 3240 / The most transparent membrane in front of the eye is called what?

The most transparent membrane in front of the eye is called what?

The most transparent membrane in front of the eye is called what?

Description

School: Clemson University
Department: Psychology
Course: Physiological Psychology
Professor: Claudio cantalupo
Term: Spring 2016
Tags: eye, Vision, visual, Fields, receptive, perception, senses, Physiology, and Psychology
Cost: 25
Name: Physiological Psychology Ch. 10
Description: These notes cover all material from Ch. 10 including visual perception, visual fields, receptive fields, the eye, etc.
Uploaded: 04/22/2017
14 Pages 48 Views 1 Unlocks
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Vision 


The most transparent membrane in front of the eye is called what?



Stimulus: visible light (form of electromagnetic energy) ∙ Visible light is a very small portion of the spectrum (just a  fraction)

o 300 nm - 750 nm

o Different wavelengths are experienced as different colors o There is no such thing as red-NESS, it is just a continuum o Colors exist only in our own experience of the world o Insects can see ultraviolet light

o Reptiles can see infrared light (heat energy)

o X ray vision goes through too many things - there is no  reflection, you wouldn't be able to see an object as well o We don't have radio waves because (you would be able to  call your friend with your mind) they are too large, they go  around things too much, you would not be able to focus on  objects


What is the meaning of lens in the eye?



If you want to learn more check out According to old thinking, the appendix is considered as what?

∙ Spectrum - starts with gamma waves (vibrate very fast, small  wavelength) - to radio waves with huge wavelengths Don't forget about the age old question of What is the number one most populated county in the world?

o Because we have a range of wavelengths - we do not  measure the frequency of them (Hz), distance measure is  preferred - distance between a wave (cycle of the wave) -  unit: nm, billionth of a meter

o Our eyes are specialized to see visible light because that  light is the most informative Don't forget about the age old question of Enumerate some factors that leads to crime.

∙ Water and gases allow light to go through them

The Eye:

∙ Cornea - most transparent membrane in front of the eye - most  important lens, allows light to go to the back of it  

o Lasik changes the properties of the cornea

∙ Lens - series of transparent, onion-like layers


The neural tissue and photoreceptors located on the inner surface of the posterior portion of the eye are called what?



o Its shape can be changed by contraction of ciliary  muscles, is flexible - the muscles attached to it pulls on the  lens allowing it to pull and thicken and allows sharper visual  perception (allows us to see something more clearly) We also discuss several other topics like Was the birth of massachusetts bay colony focused on religious liberty?

∙ Retina: the neural tissue and photoreceptors located on the  inner surface of the posterior portion of the eye

o Signal processing occurs here

o Microscopically you see receptors (specialized cells that  perform transduction - takes visual light and then causes  release of NT)

∙ Rods and cones

∙ Horizontal cell (neuron) - tend to form synaptic  connections horizontally across the retina

∙ Bipolar cells (neurons) - connect transversely across  the retina, look like dipoles

∙ Amacrine cells (neurons) - make synaptic  connections across in the horizontal direction ∙ Ganglion cells - contains optic nerve fibers -  processes and sends signal to the brain through its axons - cluster together and form a cable called the optic  nerve, carries a ton of info to the brain

∙ Layers: photoreceptor layers (rods and cones) -  bipolar layer (bipolar, horizontal and amacrine), then  ganglion cell layer Don't forget about the age old question of List down the steps on how to conduct a hypothesis test.

∙ Center of the retina is the fovea (0˚)

 There are no rods in the central region, cones  are found tightly packed in the fovea (central  region)

 Rods are found around the periphery of the  fovea If you want to learn more check out What are the different approaches on language development?

 The blind spot is in the position of the optic  nerve - nothing can be seen there - is surrounded by  rods

∙ Nothing is detected here

∙ Why is there a blind spot? Corresponds  to where the optic nerve comes out of the eye -  There is no gap in the retina, the axons of  

ganglion cells have to get out

∙ Retina is backwards

∙ Light can go through the retina - get transformed  into electricity, send excitatory NT into the cell

Simple Retina:

∙ Photopigments: light sensitive chemicals

o 1 protein + 1 vitamin (retinal)

o No light in the retina at all = sodium channels open =  membrane is depolarized = release inhibitory NT = inhibits  the activity of the bipolar and ganglion cells = you don't see  anything

o Sodium channels opening means the neurons are active o When light comes through the retina, and photons  

bombard photopigements, retinol gets knocked off, which  ultimately causes the sodium channels in the membrane of  the receptor to close

∙ Membrane becomes hyperpolarized

∙ Release of inhibitory NT is reduced

∙ Activity of bipolar cells is less inhibited, therefore  more activity occurs

∙ Firing rate increase

∙ You start seeing things

∙ Photoreceptor

o Are at the top of their activity when there is no light ∙ Bipolar cells are inhibited when there is darkness or  when photoreceptors are active

∙ Stacks of discs are folding of the cellular membrane  cells - where photopigments are (has retinol in it)

o Lines in both photoreceptors are called lamellae o Rods ~120 million

∙ No rods in the fovea

∙ Contain photopigment Rhodopsin (very sensitive to  light, rods work best in dim light)

∙ Provides us with our night vision system

∙ Detect different levels of light and dark, NOT colors ∙ Most concentrated away from fovea

o Cones (~6 million)

∙ Contain photopigment iodopsin (require high level  of light, cones work best in daylight)

∙ 3 kinds of iodopsin: each reacts to unequal  

wavelengths

 If you have a graph and compare the response  of these three types there is one type that responds  most to seeing blue; another responds most to green and the last one responds most to red

∙ Detect different colors (red, blue, green)

∙ Most concentrated in the fovea

∙ What is the connection between cones and ganglion  cells - where you start seeing visual perception?

 You would see that there tends to be a 1:1  connection between photoreceptors and ganglion  cells in the fovea - means that the patch of retina the ganglion cells are receiving information from are  extremely small  

 Receptive field in center of retina (fovea):  area of the retina from which a ganglion cell  receives input

∙ Corresponds to a cross section on a cone - tiny portion on the retina

 Receptive field in the periphery of the retina  contains one ganglion cell that corresponds to a  variety of photoreceptors (mostly rods, maybe some  cones)

 The further away you move from the center of  the retina the more photoreceptors that correspond  to one ganglion cell and you also see less cones

∙ Receptive field gets larger as you move  further away from the fovea

 Because receptive fields in the fovea are so  small - causes us to have a higher visual acuity in  the fovea - ability to distinguish details of a visual  scene

∙ As you move away from the retina, visual acuity gets sloppier and sloppier

 "Retina display" - very sharp image, you  cannot see the pixels in the screen; the pixels are  smaller than the smallest receptive field in the fovea

∙ Bipolar cell

∙ Ganglion cell

∙ Optic nerve fiber

Visual field: part of the environment that is registered on the retina  (technically both of the retinas and the image they conduct)

∙ There are two VFs one for left eye and one for right eye. They  overlap slightly (binocular field)

∙ Predators tend to have eyes that are close together on the same  plane, where as prey tend to have eyes on different planes  (different sides of the head)

∙ You see something on the left VF - not where it overlaps o The picture on the left eye is focused on the nasal side of  the left eye and then image on the right eye is focused on the temporal side of the right eye

∙ Nasal side is closest to the nose

∙ Temporal side is closest to the temporal bone on the  side of the head

o If the image was seen in the right VF the conditions would be switched

o Means that information about an object comes into parts  of BOTH eyes

∙ There is a point where the two optic nerves merge called the  optic chiasm - midline crossing of the nasal sides of the retina o Once it passes this point all information processed from an image on the left side of the visual field comes together and  all the information processed from an image on the right side of the visual field comes together (the colors come together) o This only works for stimuli that fall on the part of the  visual field that does NOT overlap

∙ Next the information goes to the Lateral Geniculate Nuclei  (LGN) of the Thalamus (major sensory relaying station for the  brain)- first brain station, relays visual information to the cortex

o MGN (medial) - relays auditory information to the cortex o 90% of fibers that come from the retina come to the  thalamus

o 10% go to the superior colliculus - part of the tectum in  the midbrain

∙ Fibers take the information from the thalamus to the primary  visual cortex in the occipital lobe

∙ This whole pathway is the retinal cortical pathway - how we  process any visual information

∙ Retinal tectal pathway: small pathway (the 10%) that is NOT  involved in giving us conscious experience from anything -  coordinating eye movements in response to visual stimulation

o Cortical blind people can see blind sight - there is a trickle of information through this pathway - it expresses itself  because visual information somehow still effects their  behavior even though they cannot see

∙ Sitting in front of a computer screen where dots of  light come on and they point to where they think the dots are - their performance is better than chance still - but  they are not aware of seeing anything at all

∙ There is no conscious experience but it still effects  their behavior

∙ Larger binocular field - fish - eyes laterally on the sides of their  head

o The advantage of our eyes being so close together -  provides the brain with most of the cues to judge distance  very effectively

∙ Retinal disparity: Discrepancy in the location of an object's  image on the two retinas as a function of the object's distance o The image that goes to the back of your eye is two  dimensional so the brain has to reconstruct the 3rd  dimension - this is made so easily because our eyes are closer together

o There is a correlation between how far an object is in  space with where the object is imaged on the retina (figure) o When an object is closer to you the eyes converge (cross eyed potentially) - when objects are farther away they  become parallel

o Detected by the visual cortex = depth perception

Color vision:  

∙ Not all species percieve in the same way (dogs and cats have a  very reduced experience of color, and some animals do not see  color at all, while others see somethings that we cannot  (ultraviolet light in insects))

∙ Colors are a produce of a brain - electromagnetic waves on a  continuum

o There are no gaps in the physical stimulus but we see the  continuum to have these gaps between colors (green to  yellow, etc.)

∙ Color vision is advantageous for primates - helps us pick out  different foods

o Berries - we can see them, they are bad for us. If we eat  them and survive we would remember that the RED berries  are no good.

∙ Gives us a selective advantage - those that cannot  see color would not be able to distinguish the bad  

berries from the good berries as easily

∙ Theories of Color Vision:

o

o People are given color cards and are asked to pick out the  pure colors - many will always pick out red, green, blue, and  yellow

o Trichromatic Theory: von Helmholtz and Young ∙ All colors are the result of the processing of three  "pure" colors: red, green, and blue, each one detected  by a specific receptor

∙ Problem; yellow also appears to observers as a  "pure" color

 Mixing light is not the same as mixing colors  (red + green + blue PAINT = brown BUT red +  

green + blue LIGHT = white)

∙ Long wavelengths are red, mid wavelengths are  green and short are blue

 When you see blue that means that it is  absorbing all the wavelengths that are not blue and  REFLECT the blue wavelengths - makes it look blue)

 When all wavelengths are absorbed we see  black and when all are reflected we see white

∙ Speculated that there were 3 types of cones, red,  green and blue

o Opponent Process Theory: Hering

∙ Explains color vision in terms of opposing neural  processes in two specific receptors

 There is something in the retina that responds  to the color in one way and opposes in another way  Red goes with green and yellow goes with blue  Processes happen in the cones

 Receptor for red and green: photochemical ∙ Shine a red light on it and it is broken  down

∙ Shine a green light on it and chemical  synthesis is boosted (catalytic effect)

 Receptor for blue and yellow: photochemical ∙ Degraded with yellow light

∙ Blue light aids build up of the  

photochemical (catalytic effect)

 Thought that there are only two types of cones in the retina, solves the problem of trichromatic  theory

∙ Explains complementary colors (color circle ex.) ∙ Also explains negative color aftereffect - class  activity

o Current theory is a combination of the two

∙ Trichromatic theory: 3 color receptors, 3 primary  colors, 3 cones (red, green and blue)

∙ Opponent process theory: 2 color receptors, 4  primary colors, 2 cones (one for red and green and  

another for blue and yellow)

∙ BOTH of them are correct - combined theory!

 3 types of cones in the retina (green, red and  blue)

 There is opponent processing - negative color  aftereffect

 4 "primary colors"

 There are certain ganglion cells in the retina  that respond to green in one way and red in the  

opposite way

 Opponent processing - happened at the  

ganglion level - NOT at the photoreceptor level,  

which was thought before

 Hurvich and Jameson - Combined Theory of  

Color Perception

 There are red/green ganglion cell and yellow  blue ganglion cells that come from the 3 color cones

∙ Red light - the red cone is most affected  

by it; when it is activated there is an inhibitory  

effect on the RG ganglion cell - fired slower -  

you see RED

∙ Close the eye there is green light on the  

retina - green cone is activated; excitatory effect

on the RG ganglion cell fires faster - you see  

GREEN

∙ Blue light - excitatory input to the YB  

ganglion cells, fires faster - you see BLUE

∙ Yellow light - between red and green,  

activates both red and green cones at the same  

time - excitatory and inhibitory cancels each  

other out - you see neither red nor green, red  

sends inputs when red and green are stimulated

simultaneously to the YB ganglion cell - inhibits  

YB ganglion cell, fires slow - see YELLOW

∙ Receptive fields of color opponent ganglion cells - opponent  response

o More efficient discrimination of number of wavelengths o Enhanced information on color contrast in objects

Form Perception: Perception of Edges

∙ Sensory system enhances perception of borders

o Mach band illusion - sudden drop in brightness at edges

∙ The band with the edge by the lighter band seems  darker than the side of the band next to the darker band  - this is an illusion because it is actually the same color. ∙ Caused by lateral inhibition

o Edge perception happens in the retina

∙ Lateral inhibition: ganglion cells inhibit and are inhibited by  neighboring cells

o We have a retina with rods, the bipolar layer excites some  cell and inhibits some neighboring ganglion cells

o Receptors 1-7 have a weak light stimulus (black) o Receptors 8-15 have a strong light stimulus (white) o Look at ganglion cell #7: receives excitatory activation  

from photoreceptor #7 and is inhibited by photoreceptor #6  and #8

∙ Inhibition is 1/4 of the stimulus of #7 for  

photoreceptor #6 (because the stimulus is weak)

∙ Excitation is +10

∙ Inhibition is 1/2 of the stimulus of #7 for  

photoreceptor #8 (because the stimulus is stronger

∙ So… +10 (excitation #7) - 2.5 (inhibition #6) - 5  (inhibition #8) = +2.5

∙ Lateral inhibition changes when you get to an edge  because there is a change in stimulus in the neighboring  photoreceptors - causing the firing rate of ganglion cells  to change

o When the retina fires slower it goes to the brain and tells  it that that region is darker than the other region

o At edges, ganglion cells get differential amounts of  inhibition from darker edge and brighter edge = makes the  edge stand out perceptually  

o Sensory system enhances perception of edges (Mach  illusion)

∙ "On-center" and "off-center" ganglion cells

o Antagonistic arrangement of receptive field

o Full stimulus on the entire receptive field: does not  change the rate of firing of the ganglion cell

o Stimulus on off center half of the receptive field:  inhibitory effect on the firing rate of the ganglion cell o Stimulus on the center and outside on one side of the  receptive field: excitatory effect on the firing rate of the  ganglion cell

∙ Receptive field: area of the retina from which a neuron receives input

∙ Retina: ganglion cells

∙ Lateral geniculate nuclei of thalamus

∙ Visual cortex

∙ Hubel and Wiesel:  

o Simple cells in visual cortex: respond to edges at a specific orientation and place of the retina

∙ 4 on center receptive fields - cause 4 excitatory  ganglion cells - goes to a single simple cell

∙ Simple cells in the primary visual cortex will start  firing faster when all four ganglion cells are firing faster  at the resting state

∙ Receptive field of the simple cell is a combination of  the individual receptive fields of the ganglion cells

o Complex cells in the visual cortex: respond to edges  moving across the retina

∙ Groups of simple cells cause stimulation of a  

complex cell

∙ Spatial Frequency theory: Some neurons perform a Fourier  analysis of the luminosity variations of a scene

o Blurring of the edges to make a pixelated picture better o Neurons in visual cortex do not detect only edges o Visual world is combination of high and low spatial  frequencies

∙ Need neurons sensitive to both

Visual Pathways:

∙ Parvocellular system: P ganglion cells project to ventral stream  ("what" system) that travels through inferior temporal lobe (from  areas V1, V2 and V4 of visual cortex)

o Then gets into the ventral side of the temporal lobe then  travels to the prefrontal cortex (executive part of the brain) o Color vision (V4) and detailed object recognition (inferior  temporal lobe)

o Color constancy (know that the color is staying the same  or changing) NOT color distinguishing (knowing WHAT color  it is - prefrontal cortex)

∙ Magnocellular system: M ganglion cells projects to dorsal  stream ("where" system) that travels to posterior parietal lobe  (from areas V1, V2 and V5)

o Brightness contrast, orientation, movement, depth and  location of objects

∙ Put them together - the prefrontal cortex then knows what  things are and where things are

Disorders of Visual Perception

∙ Object agnosia: impairment in ability to recognize objects by  sight

o Prosopagnosia: inability to recognize familiar faces  (parents/siblings)

∙ Due to inferior temporal lobe damage (fusiform face  area specialized for face recognition)

∙ Color agnosia: impairment in color perception due to brain  damage

o V1 is for wavelength discrimination; V4 is form more  complex color perception (color constancy)

∙ Movement agnosia: inability to perceive movement o Damage to area V5 (medial temporal gyrus)

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