Presentation on theme: "Chapter 4: Cortical Organization. An Exploration of Spatial Organization Electronic map on V1 –Retinotopic map is an electron map of the retina on the."— Presentation transcript:
Chapter 4: Cortical Organization
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
Figure 4-2 p78
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
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
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
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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
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The Cortex is Organized in Columns - continued Visual cortex shows –Ocular dominance columns Neurons in the cortex respond preferentially to one eye.
How Do Feature Detectors Respond to a Scene? Tiling – columns working together to cover the entire visual field.
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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.
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
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
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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.
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
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Behavior of People Without Brain Damage Ganel experiment was designed to demonstrate a separation of perception and action in non-brain-damage subjects.
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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.
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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.
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Where Vision Meets Memory MTL structures are extremely important in memory –H.M. –hippocampus
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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