1. Chapter 4: Cortical Organization

2. An Exploration of Spatial Organization
Electronic map on V1
Retinotopic map is an electron map of the retina on the cortex
Cortical magnification – a small area of the fovea is represented by a large area on the visual cortex

3. Figure 4.1 A person looking at a tree, showing how points A, B, C, and D are imaged on the retina and where these retinal activations cause activity in the brain. Although the distances between A and B and between C and D are about the same on the retina, the distance between A and B is much greater on the cortex. This is an example of cortical magnification, in which more space is devoted to areas of the retina near the fovea.
Figure 4-1 p78

4. Figure 4. 2 The magnification factor in the visual system
Figure 4.2 The magnification factor in the visual system. The small area of the fovea is represented by a large area on the visual cortex.
Figure 4-2 p78

5. Brain Imaging Techniques
Positron emission tomography (PET)
Person is injected with a harmless radioactive tracer
Tracer moves through bloodstream
Monitoring the radioactivity measures blood flow
Changes in blood flow show changes in brain activity

6. Brain Imaging Techniques - continued
PET - subtraction method
Brain activity is determined by:
Measuring activity in a control state
Measuring activity in a stimulation state
Subtracting the control activity from the stimulation activity

7. Brain Imaging Techniques - continued
Functional magnetic resonance imaging (fMRI)
Hemoglobin carries oxygen and contains a ferrous molecule that is magnetic
Brain activity takes up oxygen, which makes the hemoglobin more magnetic
fMRI determines activity of areas of the brain by detecting changes in magnetic response of hemoglobin
Subtraction technique is used like in PET

8. Figure 4.3 A person in a brain scanning apparatus.
Figure 4-3 p79

9. Figure 4.4 (a) Red and blue areas show the extent of stimuli that were presented while a person was in an fMRI scanner. (b) Red and blue indicate areas of the brain activated by the stimulation in (a).
Figure 4-4 p79

10. The Cortex is Organized in Columns
Cortical magnification factor
Fovea has more cortical space than expected

11. Figure 4. 5 Demonstration of the magnification factor
Figure 4.5 Demonstration of the magnification factor. A person looks at the red spot on the text on the left. The area of brain activated by each letter of the text is shown on the right. The arrows point to the letter a in the text on the left, and the area in the brain activated by the a on the right.
Figure 4-5 p80

12. The Cortex is Organized in Columns
Visual cortex shows:
Location columns
Receptive fields at the same location on the retina are within a column
Orientation columns
Neurons within columns fire maximally to the same orientation of stimuli
Adjacent columns change preference in an orderly fashion
1 millimeter across the cortex represents entire range of orientation

13. Figure 4. 6 Location column
Figure 4.6 Location column. When an electrode penetrates the cortex perpendicularly, the receptive fields of the neurons encountered along this track overlap. The receptive field recorded at each numbered position along the electrode track is indicated by a correspondingly numbered square.
Figure 4-6 p80

14. Figure 4. 7 Orientation columns
Figure 4.7 Orientation columns. All of the cortical neurons encountered along track A respond best to horizontal bars (indicated by the red lines cutting across the electrode track). All of the neurons along track B respond best to bars oriented at 45 degrees.
Figure 4-7 p81

15. Figure 4.8 If an electrode is inserted obliquely into the cortex, it crosses a sequence of orientation columns. The preferred orientation of neurons in each column, indicated by the bars, changes in an orderly way as the electrode crosses the columns. The distance the electrode is advanced is exaggerated in this picture.
Figure 4-8 p81

16. Figure 4.9 A location column that contains the full range of orientation columns. A column such as this, which contains a full array of orientation columns, was called a hypercolumn by Hubel and Wiesel. A column such as this receives information about all possible orientations that fall within a small area of the retina.
Figure 4-9 p81

17. The Cortex is Organized in Columns - continued
Visual cortex shows
Ocular dominance columns
Neurons in the cortex respond preferentially to one eye.

18. How Do Feature Detectors Respond to a Scene?
Tiling – columns working together to cover the entire visual field.

19. Figure 4. 10 (a) A scene from the Pennsylvania woods
Figure 4.10 (a) A scene from the Pennsylvania woods. (b) Focusing in on part of a tree trunk. A, B, and C represent the parts of the tree trunk that fall on receptive fields in three areas of the retina.
Figure 4-10 p82

20. Figure 4.11 (a) Receptive fields for the three sections of the tree trunk from Figure 4.10b. The neurons associated with each of these receptive fields are in different location columns. (b) Three location columns in the cortex. Neurons that fire to the tree trunk’s orientation are within the orange areas of the location column.
Figure 4-11 p82

21. Figure 4.12 The yellow circles and ellipses superimposed on the forest scene each represent an area that sends information to one location column in the cortex. The way these location columns cover the entire receptive field is called tiling.
Figure 4-12 p82

22. Streams for Information About What and Where
Lesioning or Ablation Experiments
First, an animal is trained to indicate perceptual capacities.
Second, a specific part of the brain is removed or destroyed.
Third, the animal is retrained to determine which perceptual abilities remain.
The results reveal which portions of the brain are responsible for specific behaviors.

23. Streams for Information About What and Where - continued
Ungerleider and Mishkin experiment
Object discrimination problem
Monkey is shown an object
Then presented with two choice task
Reward given for detecting the target object
Landmark discrimination problem
Monkey is trained to pick the food well next to a cylinder

24. Streams for Information About What and Where - continued
Ungerleider and Mishkin - Using ablation, part of the parietal lobe was removed from half the monkeys and part of the temporal lobe was removed from the other half.
Retesting the monkeys showed that:
Removal of temporal lobe tissue resulted in problems with the object discrimination task - Where pathway
Removal of parietal lobe tissue resulted in problems with the landmark discrimination task - What pathway

25. Figure 4.13 The two types of discrimination tasks used by Ungerleider and Mishkin. (a) Object discrimination: Pick the correct shape. Lesioning the temporal lobe (shaded area) makes this task difficult. (b) Landmark discrimination: Pick the food well closer to the cylinder. Lesioning the parietal lobe makes this task difficult.
Figure 4-13 p83

26. Figure 4.14 The monkey cortex, showing the what, or ventral, pathway from the occipital lobe to the temporal lobe, and the where, or dorsal, pathway from the occipital lobe to the parietal lobe. The where pathway is also called the how pathway.
Figure 4-14 p84

27. Streams for Information About What and Where - continued
What pathway also called ventral pathway
Where pathway also called dorsal pathway
Both pathways:
originate in retina and continue through two types of ganglion cells in the LGN.
have some interconnections.
receive feedback from higher brain areas.

28. Streams for Information About What and How
Where pathway may actually be “How” pathway or action pathway
Dorsal stream shows function for both location and for action.
Evidence from neuropsychology
Double dissociations: two functions involve different mechanisms and operate independently

29. Table 4-1 p85

30. Streams for Information About What and How - continued
Behavior of patient D.F.
Damage to ventral pathway due to gas leak
Not able to match orientation of card with slot
But was able to match orientation if she was placing card in a slot
Other patients show opposite effects
Evidence shows double dissociation between ventral and dorsal pathways

31. Figure 4. 16 Performance of D. F
Figure 4.16 Performance of D.F. and a person without brain damage on two tasks: (a) judging the orientation of a slot; and (b) placing a card through the slot. See text for details.
Figure 4-16 p85

32. Behavior of People Without Brain Damage
Ganel experiment was designed to demonstrate a separation of perception and action in non-brain-damage subjects.

33. (a) The size illusion used by Ganel and coworkers (2008) in which line 2 looks longer than line 1. The numbers were not present in the display seen by the subjects. (b) The two vertical lines from (a), showing that line 2 is actually shorter than line 1. (c) Subjects in the experiment adjusted the space between their fingers either to estimate the length of the lines (length estimation task) or to reach toward the lines to grasp them (grasping task). The distance between the fingers is measured by sensors on the fingers. (d) Results of the length estimation and grasping tasks in the Ganel et al. experiment. The length estimation task indicates the illusion, because the shorter line (line 2) was judged to be longer. In the grasping task, subjects separated their fingers more for the longer line (line 1), which was consistent with the physical lengths of the lines.
Figure 4-17 p86

34. Modularity: Structures for Faces, Places, and Bodies
Module - a brain structure that processes information about specific stimuli
Rolls measured the response neurons in the Inferotemporal (IT) cortex in monkeys
Responds best to faces with little response to non-face stimuli
Temporal lobe damage in humans results in prosopagnosia.

35. Figure 4.18 How a neuron in a monkey’s temporal lobe responds to a few stimuli. This neuron responds best to a circular disc with a thin bar (a).
Figure 4-18 p87

36. Figure 4.19 Size of response of a neuron in the monkey’s IT cortex that responds to face stimuli but not to nonface stimuli.
Figure 4-19 p87

37. Figure 4. 20 Results of the Tsao et al
Figure 4.20 Results of the Tsao et al. (2006) experiment in which activity of neurons in the monkey’s temporal lobe was recorded in response to faces, other objects, and a scrambled stimulus.
Figure 4-20 p88

38. Areas for Faces, Places, and Bodies in the Human Brain
Evidence from humans using fMRI and the subtraction technique show:
Fusiform face area (FFA) responds best to faces.
Parahippocampal place area (PPA) responds best to spatial layout.
Extrastriate body area (EBA) responds best to pictures of full bodies and body parts.

39. Figure 4.21 (a) The parahippocampal place area (PPA) is activated by places (top row) but not by other stimuli (bottom row). (b) The extrastriate body area (EBA) is activated by bodies (top), but not by other stimuli (bottom).
Figure 4-21 p88

40. Figure 4.22 fMRI responses of the human brain to various types of stimuli: (a) areas that were most strongly activated by houses, faces, and chairs; (b) all areas activated by each type of stimulus.
Figure 4-22 p89

41. Where Vision Meets Memory
MTL structures are extremely important in memory
H.M.
hippocampus

42. Figure 4.23 (a) Location of the hippocampus and some of the other structures that were studied by Quiroga and coworkers (2005). (b) Some of the stimuli that caused a neuron in the hippocampus to fire.
Figure 4-23 p90

43. Figure 4.24 Activity of a neuron in the MTL of an epilepsy patient as he remembered the things indicated below the record. A response occurs when the person remembered The Simpsons TV program. Earlier, this neuron had been shown to respond to viewing a video clip of The Simpsons.
Figure 4-24 p90

44. Experience and Neural Responding
Experience-dependent plasticity in humans
Brain imaging experiments show areas that respond best to letters and words.
fMRI experiments show that training results in areas of the FFA responding best to:
Greeble stimuli
Cars and birds for experts in these areas

45. Figure 4. 25 (a) Greeble stimuli used by Gauthier
Figure 4.25 (a) Greeble stimuli used by Gauthier. Participants were trained to name each different Greeble. (b) Brain responses to Greebles and faces before and after Greeble training.
Figure 4-25 p91