Chapter 3: Neural Processing and Perception

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