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2014-03-07 17:41:30
Chapter Six

The Visual System
Show Answers:

  1. What does Wavelength refer to ?
    Perception of color (400-700 nms)
  2. What does Intensity refer to ?
    Perception of brightness (Bright/Dull)
  3. What does Sensitivity refer to ?
    The ability to see when light is dim
  4. What does Acuity refer to ?
    The ability to see detail
  5. What do we see ?
    Upside down & backwards in the back of the eye ball in the RETINA
  6. How does light go through the eye ?
    • Light enters the eye through pupil (Dilates and constricts; iris (colored part)
    • Light then passes through the lens
    • Lens focuses (becomes fatter/skinnier) image on retina (skinner to see farther/ fatter to see closer)
  7. What is the Binocular Cue of Convergence ?
    Eyes must turn slightly inward when objects are close
  8. What is the Binocular Disparity ?
    Difference between the images on the two retinas
  9. What is the purpose of the Retina ?
    • Light passes through lens & focuses light on area of retina of highest visual acuity = Fovea
    • Thinning - provides less distortion (can see things clear & in detail)
    • The retina is inside-out - light passes through several cell layers before reaching its receptors

  10. RETINA
  11. What do the Photoreceptors do ?
    Light is changed into neural impulse that the brain can interpret
  12. What is the blind spot ?
    • Axons of retinal ganglion cells exit forming optic nerve
    • No receptors
  13. What is Completion ?
    • Brain uses information from cells around the blindspot to fill in missing info
    • Perceive no gaps in vision
  14. What are two types of photoreceptors ?
    • Cones
    • Rods
  15. What is Duplexity Theory of Vision ?
    Cone & Rods mediate different kinds of vision
  16. Where is the location of the Cones & Rods in the Eye ?
    • Cones: Located in the center of the Fovea
    • Rods: on the outside of the Fovea surrounding the eye
  17. Where is the location, lighting, qualities and types of vision of the Cones & Rods ?
  18. What is High Convergence ?
    • Rods
    • A lot of Convergence of Rods -> Bipolar cells -> Ganglion
    • Very sensitive
    • High Convergence = High Sensitivity = Low Acuity
  19. What is Low Convergence ?
    • Cones
    • Low Convergence = Low Sensitivity = High Acuity
    • 1:1 connection
  20. What is Saccades ?
    We continually scan the world with small and quick eye movements
  21. What is the Retinal-Geniculate-Striate Pathway ?
    • Retina->Lateral Geniculate Nucleus-> Priamry Visual Cortex (VI - Striate)
    • Eye ->Thalamus->Occipital Lobe
  22. What is the Retinotopic Organization ?
    • Each level of system = map of retina
    • Disproportionate representation of the Fovea
    • Map outside is mapped in thalamus & cortex
  23. What is Mach Band ?
    When you see edges and shadowing when there is none
  24. What does Lateral Inhibition do ?
    Contains mechanisms to enhance contrasts and make edges easier to see
  25. In our receptive fields what does On-Center Cell refer to ?
    • Light on center EXCITES cell
    • Light on surround INHIBITS cell
  26. In our receptive fields what does Off-Center Cell refer to ?
    • Light on center INHIBITS cell
    • Light on surround EXCITES cell
  27. In the Striate Cortex, neurons with circular receptive fields are rare but they are either ?
    SIMPLE: Rectangular, Static (on & off regions), orientation and location sensitive, MONOCULAR

    COMPLEX: Rectangular, larger receptive fields, are not static, motion sensitive, BINOCULAR
  28. As visual information flows through hierarchy, receptive fields become ?
    • Larger
    • Respond to more complex and specific stimuli
  29. What is the Component Theory/Trichromatic Theory ?
    • 3 different kinds of cones: red, blue, green
    • Every colour is a combination of cone responses
    • We can see color by adding color
  30. Trichromativ theory can not explain ?
    • Red-green color blind individuals who should not be able to perceive yellow
    • Afterimages
  31. What is the Opponent-Process Theory ?
    • 3 cone types
    • Each responds to 2 different wavelengths (red or green; blue or yellow; black or white
    • Explains Afterimage: stare at certain color. Neural processes become fatigued. Rebound effect; receptor responds in opposite reaction
  32. What is the Dual Process Theory ?
    • Combines Component & Opponent-process theories
    • 3 types of cones in retina
    • Opponent processes occur higher up = ganglion cells, thalamus & visual cortex
  33. What is the Cortical Pathway for Vision ?
    Thalamus (LGN) -> Primary Visual Cortex (Striate, VI) -> Secondary Visual Cortex (Prestriate, VII) -> Visual Association Cortex
  34. What is Sensation ?
    Detecting a stimulus
  35. What is Perception ?
    Understanding the stimulus
  36. What is Scotoma ?
    • Damage to Primary Visual Cortex producing blindness in the visual field
    • Completion - can not notice a persons head if has a background that is patterned
    • Not consciously aware of deficit
  37. What is Blindsight ?
    • Response to visual stimuli without conscious awareness of "seeing"
    • Catch ball tossed toward them while claiming not to see it
  38. Who is Patient TN ?
    • Suffered 2 strokes
    • blind by normal measures
    • PET & fMRI scans showed no activity in VI
    • killed the occipital lobe & primary visual cortex
  39. What are the Dorsal & Ventral Streams ?
    • 2 major streams from primary visual cortex to secondary & association cortex
    • Dorsal Stream: Where
    • Ventral Stream : What
  40. What is the Dorsal Stream ?
    • Primary visual cortex -> Dorsal Prestriate Cortex -> Posterior Parietal Cortex
    • Visual Spacial Perception
  41. What is the Ventral Stream ?
    • Primary Visual Cortex -> Ventral Prestriate Cortex -> Inferotemporal Cortex
    • Conscious Visual Pattern Recognition
  42. Who is patient A.T. ?
    • Could accurately recognize objects
    • could demonstrate the size of objects with fingers
    • Made awkward grasps; could not preshape her hand for objects Optic Ataxia
    • Damage to Dorsal Stream
  43. Who is patient D.F ?
    • Unable to recognize size, shape, or orientation of visual objects Visual Agnosia
    • If asked to place object through a slot she could do so with ease
    • Damage to Ventral Stream
  44. What is Prosopagnosia ?
    • Can readily recognize objects (tables) but are unable to recognize particular faces BUT patients also have n inability to recognize specific objects belonging to a complex class of objects (bird watch ect)
    • Problems recognizing whose face it is - see a jumble of individual face parts
    • Due to damage in Fusiform Face Stream (Ventral stream)
  45. What is the Greeble Experiment ?
    • Put into fMRI & showed Greebles & look at FFA & did not light up
    • 2 week of intense greeble & name them based on features
    • then FFA showed activation based on features
  46. Is there an unconscious recognition ?
    • Skin conducting response to familiar & non-familiar faces
    • Skin conduction was elevated even when they say they don't recognize a person but unconsciously they do
    • Implicit recognition