1. ch 31 Sensation & Perception Ch. 3: Vision © Takashi Yamauchi (Dept. of Psychology, Texas A&M University) Main topics –convergence –Inhibition, lateral inhibition and lightness perception –Interactions between neurons –Feature detectors

2. ch 32 Question 1 What do these devices have in common?

3. ch 33 These devices make use of electromagnetic waves Capture electromagnetic waves and transform them into various forms.

4. ch 34 What does the eye do?  Transducing light energy into electrical energy

5. ch 35 Transduction  Light enters the eye  A photon hits a receptor  changes the shape of pigment molecules  triggers massive chemical reactions  generate electrical signals

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7. 7 Solar cells (photovoltaics) produce electricity in a similar way as our eyes do.

8. ch 38 Rods and cones Morphology Distribution on the retina Dark adaptation Spectral sensitivity

9. ch 39 Photo receptors: Rods and cones Rods have bigger outer segments than cones. Why?

10. ch 310 Outer segments capture photons Bigger outer segments can capture more light. Rods have bigger outer segments. –Rods allow us to see in the dark. –Cones are mainly for day vision. –Cones are for color perception.

11. ch 311 How can we see a book? How can we see a desk? Why don’t we see light? How can we see objects?

12. ch 312 Reflection of light What we see is a reflection of light. Different objects reflect different wavelengths, –  different objects show different colors

13. ch 313 Photo receptors in the eye are geared to capture different wavelengths

14. ch 314 Lens: focuses light rays. Iris: control the size of the pupil  regulating the amount of light reaching the retina Retina: a layer of receptor cells Receptor cells  rods and cones

15. ch 315 Retina:

16. ch 316 Photo receptors are facing away from the light source. The optic nerve carries neural information to this spot. What happens? –No receptors, no vision  blind spot

17. ch 317 Some messages: how to improve your vision Massage your eye muscles Eat carrots Massage the back of your head.

18. ch 318 Rods and cones Morphology Distribution on the retina Dark adaptation Spectral sensitivity

19. ch 319 The distribution of cones and rods on the retina Cones are concentrated mainly on the fovea. There are no rods on the fovea. We move eyes to capture images on the fovea.

20. ch 320 Demonstration Blind spot

21. ch 321 Rods and cones are different In their dark adaptation rates

22. ch 322 Dark adaptation rates of rods and cones When you enter a dark room from outside, you can’t see well at first. But gradually, your eyes are adjusted to the dark, and see better.

23. ch 323 In terms of the activity of neurons, what is the difference between A and B ? Any guess? A. B.

24. ch 324 Measuring the electrical activity of a neuron directly by inserting a thin needle into animal brains.

25. ch 325 Time 0t The frequency of action potential Time 0t 0t The number of action potential emitted by a neuron is correlated with the intensity of the stimulus.

26. ch 326 Neural Processing by Convergence Why are rods more sensitive to light than cones? Because rods are bigger than cones. Because rods and cones are connected to ganglion cells in different manners.

27. ch 327 Activities of neurons can be schematically shown as B a1 a2 a3 a4 The firing rate of neuron B is determined by the activation sent by neurons a1-a4.

28. ch 328 Ganglion cell

29. ch 329 Convergence: The ratio of connections with two groups of neurons. Rods vs. Ganglion cells –120:1 Cones vs. Ganglion cells –6:1

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31. ch 331 Why does this matter? How is this related to the higher sensitivity of rods?

32. ch 332 The cones result in better detail vision than the rods Visual acuity –How far apart are two dots?

33. ch 333 Time 0t The frequency of action potential Time 0t 0t The number of action potential emitted by a neuron is correlated with the intensity of the stimulus.

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36. ch 336 Fig. 2.11, p.53

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40. ch 340 Demonstration: On a scratch paper, draw two vertical lines of about 2 inches (1/2 inch apart). Close your left eye, and focus your right eye on your index figure, and move the figure. At some point, you can’t distinguish the two vertical lines.

41. ch 341 The distribution of cones and rods on the retina Cones are concentrated mainly on the fovea. There are no rods on the fovea. We move eyes to capture images on the fovea.

42. ch 342 Visual Cortex

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45. ch 345 The cones result in better detail vision than the rods Visual acuity –How far apart are two dots?

46. ch 346 Neurons How do you detect there are two separate dots (lights)?

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48. ch 348 How do you detect there are two separate dots (lights)?

49. ch 349 Rods are bigger than cones Convergence:

50. ch 350 Lateral Inhibition & Mach bands

51. ch 351 Herman grid

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54. ch 354 Time 0t The frequency of action potential Time 0 t The number of action potential emitted by a neuron is correlated with the intensity of the stimulus. Time 0 t

55. ch 355 Questions: What happens to B? 0 t

56. ch 356 Questions: What happens to B? ExcitatoryInhibitory

57. ch 357 Receptive field The receptive field of a neuron in the visual system is the area on the retina that influences the firing rate (action potential) of the neuron. Measuring the receptive field of a ganglion cell

58. ch 358 Receptive field of a ganglion cell Measuring the frequency of action potentials elicited by this ganglion cell. Cones Ganglion cell B

59. ch 359 Receptive field of a ganglion cell Cones Ganglion cell B 12 3 4 5 6 7 Firing rate of B 43-52-62-7

60. ch 360 Questions: What happens to B?

61. ch 361 Measuring the receptive field of a ganglion cell Change the size of the stimulus and see the way a ganglion cell respond

62. ch 362 Cones Ganglion cell B 12 3 4 5 6 7

63. ch 363 ExcitatoryInhibitory Excitatory- center- inhibitory- surround receptive field

64. ch 364 Questions: What happens to B? ExcitatoryInhibitory

65. ch 365 Excitatory and inhibitory connections What neurons transmit is electricity. Some neurons send positive (excitatory) signals (+)  increase the firing rate of the target neuron. some neurons send negative (inhibitory) signals (-)  depress the firing rate of the target neuron.

66. ch 366 Spatial Summation c1 c2 c3 c4 B a1 a2 a3 a4 + + = 4 + + B a1 a2 a3 a4 + + = 0 + + - - - - The firing rate of neuron B can be expressed by the overall summation of the signals that B receives.

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69. ch 369 How does this happen?

70. ch 370 =sum(B)

71. ch 371 Fig. 3-6, p. 50

72. ch 372 Fig. 3-7, p. 51

73. ch 373 Why is this important?  help you to detect the edge of a figure

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75. ch 375 Light intensity location Perceived Light intensity location

76. ch 376 Physical stimuliYour perception

77. ch 377 Lateral inhibition

78. ch 378 + -- + -- 10020 + -- + --

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81. ch 381 White’s illusion Can you explain this by lateral inhibition?

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89. ch 389 Application: Machine vision Implementing the mechanism of lateral inhibition to a computer program.

90. ch 390 Image

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94. ch 394 Edge detection algorithm –Zero-crossing