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Chapter 3: Neural Processing and Perception

Chapter 3: Neural Processing and Perception. Neural Processing and Perception. Neural processing is the interaction of signals in many neurons. Figure 3-1 p54. Lateral Inhibition and Perception. Experiments with eye of Limulus Ommatidia allow recordings from a single receptor.

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Chapter 3: Neural Processing and Perception

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  1. Chapter 3: Neural Processing and Perception

  2. Neural Processing and Perception • Neural processing is the interaction of signals in many neurons.

  3. Figure 3-1 p54

  4. Lateral Inhibition and Perception • Experiments with eye of Limulus • Ommatidia allow recordings from a single receptor. • Light shown into a single receptor leads to rapid firing rate of nerve fiber. • Adding light into neighboring receptors leads to reduced firing rate of initial nerve fiber.

  5. Figure 3-2 p54

  6. Figure 3-3 p55

  7. Lateral Inhibition and Lightness Perception • Three lightness perception phenomena explained by lateral inhibition • The Hermann Grid: Seeing spots at an intersection • Mach Bands: Seeing borders more sharply • Simultaneous Contrast: Seeing areas of different brightness due to adjacent areas

  8. Hermann Grid • People see an illusion of gray images in intersections of white areas. • Signals from bipolar cells cause effect • Receptors responding to white corridors send inhibiting signals to receptor at the intersection • The lateral inhibition causes a reduced response which leads to the perception of gray.

  9. Figure 3-4 p55

  10. Figure 3-5 p55

  11. Figure 3-6 p56

  12. Figure 3-7 p56

  13. Figure 3-8 p56

  14. Mach Bands • People see an illusion of enhanced lightness and darkness at borders of light and dark areas. • Actual physical intensities indicate that this is not in the stimulus itself. • Receptors responding to low intensity (dark) area have smallest output. • Receptors responding to high intensity (light) area have largest output.

  15. Figure 3-9 p57

  16. Figure 3-10 p57

  17. Mach Bands - continued • All receptors are receiving lateral inhibition from neighbors • In low and high intensity areas amount of inhibition is equal for all receptors • Receptors on the border receive differential inhibition

  18. Mach Bands - continued • On the low intensity side, there is additional inhibition resulting in an enhanced dark band. • On the high intensity side, there is less inhibition resulting in an enhanced light band. • The resulting perception gives a boost for detecting contours of objects.

  19. Figure 3-9 p57

  20. Figure 3-12 p58

  21. Figure 3-13 p58

  22. Lateral Inhibition and Simultaneous Contrast • People see an illusion of changed brightness or color due to effect of adjacent area • An area that is of the same physical intensity appears: • lighter when surrounded by a dark area. • darker when surrounded by a light area.

  23. Lateral Inhibition and Simultaneous Contrast - continued • Receptors stimulated by bright surrounding area send a large amount of inhibition to cells in center. • Resulting perception is of a darker area than when this stimulus is viewed alone. • Receptors stimulated by dark surrounding area send a small amount of inhibition to cells in center. • Resulting perception is of a lighter area than when this stimulus viewed alone.

  24. Figure 3-14 p58

  25. Figure 3-15 p59

  26. A Display That Can’t Be Explained by Lateral Inhibition • White’s Illusion • People see light and dark rectangles even though lateral inhibition would result in the opposite effect.

  27. Explanation of White’s Illusion • Belongingness • An area’s appearance is affected by where we perceive it belongs. • Effect probably occurs in cortex rather than retina. • Exact physiological mechanism is unknown.

  28. Figure 3-16 p59

  29. Figure 3-17 p59

  30. Figure 3-18 p60

  31. Processing From Retina to Visual Cortex and Beyond • Area of receptors that affects firing rate of a given neuron in the circuit • Receptive fields are determined by monitoring single cell responses. • Research example for vision • Stimulus is presented to retina and response of cell is measured by an electrode.

  32. Figure 3-19 p60

  33. Figure 3-20 p61

  34. Figure 3-21 p61

  35. Center-Surround Antagonism • Output of center-surround receptive fields changes depending on area stimulated: • Highest response when only the excitatory area is stimulated • Lowest response when only the inhibitory area is stimulated • Intermediate responses when both areas are stimulated

  36. Figure 3-22 p62

  37. Figure 3-23 p62

  38. Hubel and Wiesel’s Rational for Studying Receptive Fields • Signals from the retina travel through the optic nerve to the • Lateral geniculate nucleus (LGN) • Primary visual receiving area in the occipital lobe (the striate cortex or area V1) • And then through two pathways to the temporal lobe and the parietal lobe • Finally arriving at the frontal lobe

  39. Figure 3-24 p63

  40. Figure 3-25 p63

  41. Hubel and Wiesel’s Rational for Studying Receptive Fields - continued • LGN cells have center-surround receptive fields. • Major function of LGN is to regulate neural information from the retina to the visual cortex. • Signals are received from the retina, the cortex, the brain stem, and the thalamus. • Signals are organized by eye, receptor type, and type of environmental information.

  42. Hubel and Wiesel’s Rational for Studying Receptive Fields - continued • Excitatory and inhibitory effects are found in receptive fields. • Center and surround areas of receptive fields result in: • Excitatory-center-inhibitory surround • Inhibitory-center-excitatory surround

  43. Figure 3-26 p64

  44. Receptive Fields of Neurons in the Visual Cortex • Neurons that fire to specific features of a stimulus • Pathway away from retina shows neurons that fire to more complex stimuli • Cells that are feature detectors: • Simple cortical cell • Orientation tuning curve • Complex cortical cell • End-stopped cortical cell

  45. Figure 3-27 p65

  46. Figure 3-28 p65

  47. Figure 3-29 p66

  48. Table 3-1 p66

  49. Selective Adaptation • Neurons tuned to specific stimuli fatigue when exposure is long. • Fatigue or adaptation to stimulus causes • Neural firing rate to decrease • Neuron to fire less when stimulus immediately presented again • Selective means that only those neurons that respond to the specific stimulus adapt.

  50. Figure 3-30 p67

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