Psy393: Cognitive Neuroscience Prof. Anderson Department of Psychology Week 3 Functional imaging Brain recording in neurologically intact brains Not anatomical/structural imaging: Static CT, MRI Physiological/functional imaging: Dynamic 2 classes Electrical EEG, ERP Metabolic fMRI, PET Large populations of synchronous neural firing Produce electrical potentials Skull and scalp passively conduct signals that can be amplified and measured Stadium/microphone analogy Single voice Cheering crowd Electroencephalography (EEG) EEG signal: Dipoles Excitatory inputs (EPSPs) Relative depolarization of dendrites relative to cell body Creates voltage difference dipole Important for studying sleep, diagnosing epilepsy and brain damage Signature rhythms relate to state of arousal Beta: alert, low amplitude, high frequency Alpha: resting with eyes closed, high amplitude Theta: deeply relaxed EEG signal: Brainwaves EEG records global brain activity over long time period Represents neural rhythms Not relative to a stimulus ERPs are a special case of EEG Align signal to onset of a stimulus or response Event-Related Potential (ERP) Average EEG trace from a large number of trials Noise cancels out Evoked Response Potentials: Evoked brainwaves
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Psy393: Cognitive Neuroscience
Prof. AndersonDepartment of Psychology
Week 3
Functional imagingBrain recording in neurologically intact brains
Where does the signal come from?The first brain imaging exp
“[In Mosso’s experiments] the subject to be observed lay on a delicately balanced table which could tip downward either at the head or at the foot if the weight of either end were increased. The moment emotional or intellectual activity began in the subject, down went the balance at the head-end, in consequence of the redistribution of blood in his system.”
-- William James, Principles of Psychology (1890)
Angelo MossoItalian physiologist
(1846-1910)
Origin of fMRI signal: BOLDBlood Oxygenation Level Dependent signal (BOLD)
Why? Deoxy hemoglobin has increased magnetic properties (paramagnetic)Ratio of oxygenated blood (arteries) to deoxy (veins) increases with neural activity
Do to increased blood flow, but same O2 extraction Results in decreased magnetic susceptibility
Brain to mind: How does neural organization relate to human perception?
Review: Is vision analytic or synthetic?
Visual maps: Multiple neural representations of reality
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Vision as analytic vs. synthetic
Analytic/constructivistConstruct perception through assembly of its partsFeature extraction —> Object perception
Synthetic/gestaltWhole more than sum of partsObject perception —> feature extraction
Neural divergence
Neural convergence
This week
Overview of visual neural pathwaysParallel processing I: Two main receptor types
Two types of visionCones: High acuity, lower sensitivityRods: Low acuity, higher sensitivity
Different topographyOrigin of M & P
Cones: ParvoRods: Magno
Other receptor types as well:Retina-SCN: Regulation of circadian rhythms
Ganglion cells
Middle layer
Receptor cells
Fovea
Cones
Rods
RodsRods
Eye to CNS: Parallel processing II
Two pathwaysRetino-geniculate-striate pathway Retino-collicular-pulvinar pathway
Retino-geniculate-striate pathVision for perception: “What” systems
Conscious visionCortical blindness: Hemianopia
“Blindsight”Weiskrantz
Nonconscious sightMay be due to spared
CortexSpared retino-collicular
path
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Retino-collicular-pulvinar pathVision for action: “Where” systems
Evidence for action vs. perceptionStimulus present in intact and blind fieldsslowed during eye movement, not detection
Retina—>Suprachiasmatic nucleus
Other forms of nonconscious visionNon-rod, non-cone, melatonin based photoreceptors
Regulation of circadian behaviorMutant mice lacking rods and cones demonstrate phase shifting to lightSupported by connection between retina and SCNConclude: Many types of “vision”
Retino-geniculate pathwayOrganization of LGN: Laminar structure
Retinal originTemporal/Nasal adjacent (Same VF)
Retino-geniculate pathway: Parallel processing III
Organization of LGN: 2. Retinotopy
6 representations of retina in register
Retino-geniculate pathway
Organization of LGN: 3. MorphologyNot all retinal maps the same
Parvocellular (P)Small cellsTop 4 layers
Magnocellular (M)Large cellsBottom 2 layers
Organization of visual cortex: Divide & Conquer!
Bifurcations and more bifurcations
LGN —> V12 divisions
M & P
V1 —> extrastriate Even greater divergenceMaintain M & P origin
Differ in features (Parallel)& complexity (Hierarchical)
Increase in RF size
Parvo
Magno
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Primary visual cortex: Striate cortex/V1/Area 17
First cortical synapse in vision: Calcarine sulcus
Striate cortex (V1): Retinotopy
6 LGN maps—>1 striate map
Striate cortex (V1): M & P segregation
Distinct laminar projections
Striate cortex (V1):Eye, orientation selectivity
Ocular dominance columns (Retained from LGN)Diff from LGN:Orientation selectivity
Increase in complexityto LGN (center-surround)
Higher order visual cortex:Extrastriate cortex
CytoarchitectureCellular correlates
More complex featuresE.g., Motion, MT/V5Direction and speed
selective
What about humans?Human visual cortex: Striate (V1)
Retinotopy (traveling wave method)Eccentricity
Foveal distortionPolar angleDefines distinct areas
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Human visual cortex: Ocular dominance columnsHigh resolution fMRI distinguishes ODC
Human visual cortex:Extrastriate cortex
Human V4: Isoluminant colorLingual, fusiform gyrus
Human MT (V5): MotionMiddle temporal gyrus
QuickTime™ and a YUV420 codec decompressor are needed to see this picture.
V1 and MT activation Levels of cortical processing:Early vs. late
Does motion perception depend on V1 (early processing)?Motion illusions: No retinal motion
Doesn’t activate V1 activate MT
Musical epilepsy? (Sacks book)
Conceptual motion: MT
What about no percept of motion?Moving vs. static ringsStatic images
Implied motion vs. no motion
Neuropsychological evidence:
RetinotopyVisual field deficits: Scotomas
Cortical blindness
Distinguish between peripheral (retinal) and central (cortical) blindness?
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Neuropsychological evidence:
Color (V4) and Motion (MT)Fractionation of perceptionAchromatopsia
HemiachromatopsiaAkinetopsia
Parallel processing, feature maps, and perceptual
experienceEvidence from human performance (Cognitive psychology)
How does the existence of multiple parallel cortical feature maps relate to human perception?
Thought experiment: If brain organized differently, what would perception be like?
Convergence between perceptual and neural evidence ?
Feature maps: Evidence from visual search
Feature vs. conjunction search (Treisman)Serial
Color and orientationParallel (“Pop out”)
E.g., Color, orientation
WSet size
Res
pons
e tim
e
Conjunction
Feature
Look for green T
Perceptual primitives:What makes a “feature”?
Perceptual primitivesBuilding blocks of perceptionRelation to cortical feature
Maps?Luminance, orientation, color,
Motion, depth
Higher-order objectsSynthesis of primitivesObjects defined by
conjunctions of primitives Share primitives
Unique primitives
Integration (binding) across feature maps
Synthesis requires attention—allows coherence across feature maps: Objects
• W/out attention Illusory conjunctions
Human perception: M & P pathways
Do M & P pathways represent different modes of perception?
Isoluminance studies Depth/Motion when defined
by luminanceNot color (isoluminant)
Depth Motion
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Conclusion: Vision as a synthetic process
How does it all come together? Independence (analytic) and convergence (synthetic)
Synthesis/ConvergenceVisual perception of form
Multiple representationsLuminance, color, motion, depth come together to produce “form”How come together: 1) Neural convergence, 2) Temporal Synchrony