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Basics of Human Vision I

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Basics of Human Vision I Basics of Human Vision I Ali Borji The Human Eye: Structures We will look at the following parts: Take notes on this page… PARTS: Cornea CORNEA (clear lens in front of eye) ● transparent covering of the front of the eye ● Allows for the passage of light into the eye and functions as a fixed lens. FUNCTION of Cornea allows for the passage of light into the eye and it also focuses the light PARTS: Pupil PUPIL (black hole) ● black hole in iris ● where light enters Pupil size is controlled by iris muscles FUNCTION of Pupil the hole where light enters into the eye THE EYE: PUPIL When the eye needs more light to enter (when it is dark), the pupils get larger; allowing more light to enter the eye THE EYE: PUPIL When the eye needs less light to enter (when it is very bright), the pupils get smaller; allowing less light to enter the eye PARTS: Iris IRIS (colored part) ● colored part of eye ● controls light entering The iris is a colored, circular muscle FUNCTION of Iris controls the amount of light entering the eye PARTS: Sclera SCLERA – a tough white skin (made of tissue) that covers all of the eyeball except the cornea. SCLERA (white part) ● whites of the eye ● supports eyeball ● provides attachment for muscles FUNCTION of Sclera supports eyeball and provides attachment for muscles PARTS: Lens LENS (lens behind pupil) ● converging lens ● allows us to see objects near and far FUNCTION of Lens allows us to see objects near and far PARTS: Retina RETINA ● internal membrane ● contains light-receptive cells (rods and cones) ● converts light to electrical signals FUNCTION of Retina converts light waves to electrical signals PARTS: Optic Nerve OPTIC NERVE ● Transmits electrical impulses from retina to the brain ● Creates blind spot ● Brain takes inverted image and flips it so we can see FUNCTION of Optic Nerve Transmits electrical signals from retina to the brain PARTS: Blind Spot BLIND SPOT • On retina where optic nerve leads back into the brain • No rod or cone cells • Other eye compensates for this area FUNCTION of Blind Spot ●Small spot on the back of the retina ●Other eye compensates for this area • Try this test to prove you have a blind spot… THE EYE: Blind Spot • On retina where optic nerve leads back into the brain • No rod or cone cells • Other eye compensates for this area • Try this test to prove you have a blind spot… PARTS Blind Spot (Optic Disk) Close your right eye and look directly at the number 3. Can you see the yellow spot in your peripheral vision? Now slowly move towards or away from the screen. At some point, the yellow spot will disappear. Your 2 Lenses: Cornea and Lens • There are two lenses in your eye, the cornea and the lens. • The cornea, the front surface of the eye, does most of the focusing in your eye • The lens provides adjustable fine-tuning of the focus FUNCTIONS: How Your Lens Focuses • Your lens has a small depth of field – You can't see something close and far with both objects in focus at the same time • Hold out your thumb about a foot away from your eye – Then, alternately focus on thumb and me (right above your thumb) • Note that you cannot see both me and your thumb sharply (in focus) at the same time – You focus on one or the other by changing the bulge of your lens thumb is out of focus less bulgy teacher is in focus thumb is in focus more bulgy Teacher is out of focus Focusing Problems HYPEROPIA • Far-sightedness • Problem seeing close objects • Distance between lens and retina too small • Light focused behind retina • Corrected with converging lenses Far-Sighted (Hyperopia) Focusing Problems PRESBYOPIA • Form of far-sightedness • Harder for people to read as they age • Lens loses elasticity • Corrected by glasses with converging lenses Focusing Problems MYOPIA • Near-sightedness • Problem seeing objects far away • Distance between lens and retina too large • Light focused in front of retina • Correct with diverging lenses Near-Sighted (Myopia) Diseases of the Eye ASTIGMATISM • Eye cannot focus an object’s image on a single point on retina • Cornea is oval instead of spherical • Causes blurred vision • Some types can be corrected with lenses Diseases of the Eye GLAUCOMA • Group of diseases • Affects optic nerve - pressure • Loss of ganglion cells • Gradual loss of sight and eventual blindness • Check eyes regularly • Can be treated Diseases of the Eye CATARACTS • Clouding forms in lens due to denaturing of lens protein • Obstructs passage of light • Caused by age, chronic exposure to UV, or due to trauma • Removed by surgery Vision Correction CONTACT LENSES • Artificial lens placed over cornea • Same as glasses • Corrects for both near and far-sightedness • Also used for cosmetic purposes (eye colour, Hollywood) Videos “How Eyes Work: An Introduction” (10:48) http://www.youtube.com/watch?v=SCn83DHC1Ug Bill Nye The Science Guy on the Eyeball (2:12) http://www.youtube.com/watch?v=cFVbLnXWn6A “How the Human Eye Works” http://www.youtube.com/watch?v=fn6v3SkH0LI The Human Eye and How it Works (22:59) http://www.youtube.com/watch?v=28NysX8JHDo Optical Illusions Can your eyes/ brain be tricked? The Human Eye • Your eyes are about to get a workout. Have you stretched your eye muscles yet? • No? Then do that now! Are you seeing spots? Look at the cross for 10 seconds. What do you see? Are these lines bent….? …or straight? What shapes do you see? Do you see the rabbit or the duck? What is wrong with Readingwith this sentence? Aoccdrnig to rscheearch at Cmabrigde Uinervtisy, it deosn't mttaer in waht oredr the ltteers in a wrod are, the olny iprmoetnt tihng is taht the frist and lsat ltteer be at the rghit pclae. The rset can be a toatl mses and you can sitll raed it wouthit a porbelm. Tihs is bcuseae the huamn mnid deos not raed ervey lteter by istlef, but the wrod as a wlohe. Read This Out Loud. Are You Sure? Read again. Blind Spot • On retina where optic nerve leads back into the brain • No rod or cone cells • Other eye compensates for this area • Try this test to prove you have a blind spot… Blind Spot (Optic Disk) Close your right eye and look directly at the number 3. Can you see the yellow spot in your peripheral vision? Now slowly move towards or away from the screen. At some point, the yellow spot will disappear. Now stare at the red dot with your right eye from 12 inches, covering your left eye with your left hand. Notice that the gap in the blue bar fills in (completes). Move your left hand to unblock your left eye and the gap re-appears. Close left eye and approach screen while staring at the letters…watch the dot! Optical Illusion Video Clips 10 Best Optical Illusions of 2014 (10:18) http://www.youtube.com/watch?v=VxTFGVp2R-8 Moving Illusions (10:47) http://www.youtube.com/watch?v=Iw8idyw_N6Q https://forum.davidicke.com/showthread.php? t=114249&page=3 The Human Eye: Physiology History of Eye Understanding 73 ▪ Plato, 427-347 B.C. ▪ Alhazen, Arabic inner fire in the eye philospopher, + emanated ray 965-1040, idea of ▪ Epicurus, 341-270 pinhole camera B.C., replicas of the ▪ Jonannes Kepler, object into the mind 1571-1630, knew ▪ Galen, 130-200, lens, put it into an physiological details, initial theory close to rays out and in current Human Visual System 74 Visual Areas of the Human Cortex 75 A Navigation, direction, obstacles B A B Saccade control D F Ι C Pursuit control E D Understanding, focus, manipulation control C E Drawing, writing 3/4 V1 F Calculation ΙΙ 2 1 Categorization 1 Recognition, 2 objects in context 3 Calculation 4 Reading Ι Recognition of actions ΙΙ Emotions Neuron 77 Neuron 2 78 Visual Fields 79 Rabbit Human Human Eye – cross section 1 80 Human Eye – cross section 2 81 Directional sensitivity 82 Retina 1 83 Light path Retina 2 84 Retina 3 85 Rods and cones 86 Light path Inside the rod and the cone 87 Cones under electron microscope 88 Response to a light slit 89 Iris - smoothing https://en.wikipedia.org/wiki/Iris_dilator_muscle 90 Use both eyes…at arm’s length, center target within finger OK sign Lock hand in position…see which eye is still aligned by closing the other The eye with good alignment is your dominant eye! http://www.twohotpotatoes.com/wp-content/uploads/whose- plate-4-tips-table-manner-03-af.jpg https://www.reddit.com/comments/uk6z1/ heres_a_neat_trick_to_determine_your_dominant_eye/ Figure 46-7 Insects appear to have two eyes also, but they are compound! Each ommatidium sends separate information to their brain. Ommatidia are the functional units of insect eyes. Ommatidia contain receptor cells that send axons to the CNS. Ommatidia Lens Receptor cells Axons https://www.google.com/search? q=plenoptic+camera&espv=2&biw=1338&bih=686&source=lnms&tbm=isch&sa=X&ved=0 ahUKEwj9_YuhpOXMAhUFKB4KHU5TD0EQ_AUICCgD&dpr=2 https://en.wikipedia.org/wiki/Light-field_camera Human vs Insect Vision Copyright Norton Presentation Manager Copyright Norton Presentation Spiders have up to 8 eyes looking in different directions!! It makes you wonder what exactly they see! http://farm5.static.flickr.com/4010/4682587135_b91e399914.jpg Vertebrate Eye senses image focuses image blind spot Copyright Norton Presentation Manager Copyright Norton Presentation What? controls light sends image to brain Use right eye only (close left eye)…focus only on the target for this test! Lock head in position…hold one finger up at arm’s length to cover view of target Move arm slowly outwards from target (to right for right eye) Find your blind spot for that eye…is it only off to ONE side? try the other side! Does the blind spot extend upwards or downwards? http://us.123rf.com/400wm/400/400/rebirth3d/rebirth3d1103/ rebirth3d110300047/9130190-woman-hand-with-index-finger-pointing- up-or-showing-number-one.jpg Try with your left eye…is its blind spot on the same side or on the other? Try with BOTH eyes open…do you have a blind spot now? Why not? Use right eye only (close left eye)…our target is a row of numbers 1 2 3 4 5 6 7 8 9 Focus on each number in turn, until the break in the blue lines is in your blind spot.
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