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Chapter 4: Cortical Organization

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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. 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

4 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

5 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

6 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

7 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

8 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

9 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

10 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

11 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

12 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

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

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

15 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

16 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

17 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

18 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.

19 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

20 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 - What pathway Removal of parietal lobe tissue resulted in problems with the landmark discrimination task - Where pathway

21 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

22 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

23 Streams for Information About What and How
Where pathway may actually be “How” pathway or action pathway Shows function for both location and for action.

24 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

25 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

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

27 (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

28 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.

29 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

30 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

31 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.

32 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

33 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

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

35 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

36 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

37 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

38 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

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