2012 Ch4 Vision


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2012 Ch4 Vision

  1. 1. What is it like to live without 1 or 2 of your basic senses? Helen Anne Keller Sullivan Video Clip – Cochlear Implant
  2. 2. What IsSensation?There are 6 - 8 Sensory SystemsNone of these are paranormal. (Ex- ESP)The Basic Five were:Vision, Hearing, Taste, Smell, and Touch Added to the Basic 5 are: Balance, Kinesthetic (sense of weight, strain, and position of joints & muscles in space) and Pain. (blocking pain video clip)
  3. 3. Sensory ThresholdsSensation & Perception: The Basics Sensation – information which we receive from the the environment
  4. 4. The Basics Perception – the process through which we interpret sensory stimulation. Perception Reflects • Learning • Expectations • Attitudes
  5. 5. Psychophysics The study of the relationshipbetween the perceived magnitude(strength) of a stimulus versus the physical magnitude of the stimulus. (measurable)
  6. 6. • Threshold - The minimal values ofsensory stimulation needed totrigger a reaction• Absolute Threshold – stimulusvalue which is detectable 50% ofthe time.• Difference Threshold – Thesmallest change in stimulationyou can detect.
  7. 7. VISION
  8. 8. LIGHT Electromagnetic energy described in wavelengths Main colors of the spectrum: ROYGBIV
  9. 9. PUPIL Dark center in middle of iris  Pupil determines how much light is let into the eye.  Changes sizes to accommodate amount of light available.
  10. 10. LENS  Transparent structure inside eye  Focuses light rays onto retina.  Adjusts to the distance of objects by changing its thickness (squint)Eye Cataract
  11. 11. RETINA Neurons (Nerve layer) lining back of eye. Retina senses light and creates impulses sent through optic nerve to the brain. Contains (photoreceptors) that process visual stimuli Photoreceptors = rods, cones
  12. 12. Macula
  13. 13. OTHER Macula -- a small area in the retina that contains special light-sensitive cells. The macula allows us to see fine details clearly. Vitreous -- the clear, jelly-like substance that fills the middle of the eye.
  14. 14. BLIND SPOT Part of retina containing no photoreceptors. This is where Optic Nerve leaves the eye A Baby’s Brain and Vision
  15. 15. RODS & CONES Rods – respond to varying degrees of light & dark; night vision; black & white  More Rods than Cones  @95% - > 120-125 million Cones – mainly color vision  Function in low light, white, black, gray. Detects movement.  @5% (@ 5 - 10 million
  16. 16. RODS & CONES (2) Cones  Cones - thick + tapered  Bright light, Movement, Whites, Blacks  Fovea -- Center of eye w/only cones (@100,000) See in colors.  Visual Acuity or sharpness of sight. http://escience.anu.edu.au/lecture/cg/Color/theFovea.en.html
  17. 17. RODS & CONES (3) 3 Types of Cones  Respond to Various wavelengths of color spectrum  Eyes most sensitive to Green/ Yellow under equal intensity of light.
  18. 18. 3 Theories of Color Vision  Trichromatic Theory  Red,Green & Blue Cones  Correspond to short, medium, & long waves of light  *Explains Color Blindness  Opponent Process Theory  Cones Work in Pairs  Red - Green & Blue - Yellow  Integrated Theory  Trichromatic and Opponent Theories work together at different stages
  19. 19. COLOR BLINDNESS Partial or total inability to distinguish color  Why? absence of, or malfunction in, the cones 3 types of Cones  Each sensitive to portion of light spectrum--red, blue, and green Color perception results from the simultaneous stimulation of 3 cone types (trichromat)
  20. 20. COLOR BLINDNESS “Trichromats” = People who see all colors (Greek term meaning “three colors”) “Dichromats” = Small number of people see only two colors and the third registers as a shade of gray. Monochromats = See the world in only black and white. Occurs in about 1 in every 100,000 men.
  21. 21. COLOR BLINDNESS Colorblind men were recruited during WWI as bombardiers b/c they would not be fooled by camouflage on the ground.
  22. 22.  Color blindness - 1  May be a hereditary condition or caused by disease of optic nerve or retina.  Acquired color vision problems affects only the eye with the disease and may become progressively worse over time.  Patients with a color vision defect caused by disease usually have trouble discriminating blues and yellows.  Patients with a color vision defect caused by disease usually have trouble discriminating blues and yellows.
  23. 23. COLOR BLINDNESS -2 Inherited color blindness is most common, affects both eyes, and does not worsen over time. Found in about 8% of males and 0.5% of females. These color problems are linked to the X chromosome and are almost always passed from a mother to her son..
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  27. 27. COLOR VISION Color Circle/Wheel = shows how complementary colors appear opposite one another on a color wheel
  28. 28. COLOR VISION Afterimage = visual sensation that occurs after the original stimulus has been removed
  29. 29. -Stare at the eye of the red parrot while you count slowly to 20, then lookimmediately at one spot in the empty bird cage. The faint, ghostly imageof the blue green bird will appear in the cage.
  30. 30. -Try the same thing with the green cardinal. A faint magenta bird will appear in the cage.
  31. 31. What Do Animals See? Animal VisionMost diurnal (daytime) animals see in color,while most nocturnal (night) animals don’t —but even here there are exceptions.
  32. 32. When considering whether animals see in color,one approach is to look to the structure of theeyes to see if cones are present. Many nocturnalanimals that scientists have studied lack cones,relying instead on greater numbers of rods forextended night vision and keener detection ofmovement. As an exception to the nocturnalrule, owls do have cones, leading scientists tobelieve these animals see in color. Most speciesof primates, birds, cats and dogs also see incolor to some degree.
  33. 33. • Humans three sets of cones fordetecting color in differentwavelengths each cone detects awide spectrum that overlaps tocreate other hues. • Animals like cats and dogs have two sets of cones, making them color-blind to specific colors. They do, however, have many more rods than humans, giving them greater night vision and a keener ability to detect motion.
  34. 34. Dogs can’t distinguish between green and orange which will both look grayish . Green and Orange appear as differing shades of gray to a dog. Feline (cats) see in color, but they have trouble distinguishing reds. . .. Reds appear as differingshades of gray to a cat. It is believed both dogs and cats see mainly in grays, yellows, and blues OTHER ANIMALS
  35. 35. ADAPTATION Dark adaptation = rods & cones become more sensitive to light (entering a dark room) Light adaptation = r & c become less sensitive (leaving dark room into light)
  36. 36. VISUAL ACUITY Sharpness of vision FOVEA Determines the ability to see visual details (Eye exam – Snellen chart) near/far sighted20/20 vision is a measurement of visual acuity.• Explanation - 20/20 means a person cansee small detail from 20 feet away -- the sameas a person with normal eyesight would seefrom 20 feet.
  37. 37. • It is possible tohave vision superior to 20/20: Maximum acuity of the human eyewithout visual aids around 20/15 to 20/10.