Upload
brittney-batt
View
218
Download
0
Tags:
Embed Size (px)
Citation preview
Electroencephalogram (EEG) and Event Related Potentials
(ERP) Lucy J. Troup
28th January 2008
CSU Symposium on Imaging
Electroencephalography (EEG)
• What is measured?– electrical changes in groups of neurons
• How is it measured?– Difference between two electrodes
• What types of changes can be measured?– Sleep-related; Certain neurological disorders
• How are these changes measured?– Frequency, Amplitude, Specific Wave-Types
• ERPs
– “Electrical Potentials associated with specific sensory, perceptual, cognitive, or motor events”
• From EEG to ERP…– Time-locked average of EEG from many trials
involving same ‘event’– Signal/Noise Ratio reduction; what is left is
‘related to the event’• EEG = 20-50v / ERP = 1-10 v
What are Event-Related Potentials?
Filter & Amplify
Average across Trials &
Individuals
Collapsed to form a “Grand Average” Or
mean of means
Electrical activity at the onset of a
stimulus recorded
Time-locking + Signal/Noise Ratio Reduction=
ERP derived from EEG
Single Trial: 100ms visual stimulus
Average of 200 trials to same stimulus
Where do potentials come from?• Not action potentials…
•ExcitatoryPostSynapticPotential’s
•InhibitoryPostSynapticPotential’s
•Most likely source
• ERP Components
– “Scalp-recorded neural activity that is generated in a given neuroanatomical module when a specific computational operation is performed”
– Peaks are not necessarily the same as components; “peaks are not special”
– Peaks are comprised of summation of latent components that are not observable, how we analyze our ERP data will relate to the validity and accuracy of our observations
How do we analyze ERP waves?
Classic Approaches to Analysis
• Parametric Statistical comparisions– Peak to Peak– Mean Amplitude– Peak Latency
• Covariation– PCA
• Source Localization– BESA
Well-studied ERP components
• Visual– C1, P1, N1, N170
• Auditory– BER, N1, MMN
• Cognitive– N2b, N2pc, P3, N400, ERN, FRN, RP, LRP
ERP precautions
• Can’t determine Where, only When
– Scalp Topography vs Source Analysis
• Doesn’t measure all neural activity
– Closed vs Open Fields
• Can only use when time-locking is practical
– Not applicable for all areas of psychology
• Artifacts– Eye blinks, mm. mvt, etc.– Lights, and other electrical sources
• Data Analysis Techniques– Artifact detection & rejection– Filtering– Reference electrodes (i.e. linked ears)– Time-locking (stim or resp?)– Segmenting (epochs, i.e. time windows)
Some potential problems
What information does a “component” provide for us?
Example from Troup, Pitts, Draper & Catellier (2007)
Electrical Geodesics Inc. 128 channel high density EEG
Example of a raw face
Example of a Gabor face
Experiment 1• N=19• Raw and Gabor Faces • Presented randomly • 3 blocks of 66 faces
ISI 500ms
Fixate 250ms
Face 1 250ms
Face 2 250ms
Response Time 1000ms
Example of Same Face Pair Example of Different Face Pair
Experiment 2• N=19• 7 Blocks 80 pairs per block• S’s respond with key press to “Same Face pairs”
Questions
• Does N170 differ in amplitude and/or latency for Gabor-filtered versus Raw face images?
• Does N170 differ in amplitude and/or latency for Gabor-filtered versus Raw for Scalp location?
• Does N170 differ in amplitude and/or latency under the manipulation of same/diff face pairs in a rapid judgment task?
Raw-Gabor Raw Same-Different
Scalp LocationScalp LocationFrontalFrontal
Left TemporalLeft TemporalRight TemporalRight Temporal
CentralCentralCenter OccipitalCenter Occipital
Behavioral ResponseBehavioral ResponseSame CorrectSame CorrectDifferent CorrectDifferent CorrectSame IncorrectSame Incorrect
Stimulus Stimulus typetype
Raw Raw GaborGabor
Amplitude and Latency
Same/Different Grand Average Data
Sig. Diff for Correct Vs Incorrect
Visual Sensory GatingTroup, Yadon, Pitts & Hafer-Zdral
(2007/2008)
• Sensory Gating– The process of “gating out’ or not responding to a
subsequent stimulus after the onset of the initial stimulus in rapid presentation
– Auditory Stimuli “clicks”– Visual Stimuli “Flashes”
• Term used interchangeably with “Habituation”• Are they fundamentally distinct or same
process?• Do people behave to visual stimuli in same way
as auditory?
ISI 500ms
Fixate 10s
Flash 1 12ms
Flash 2 12ms
ISI 500ms
Flash 6 80ms
ISI 1200ms
Flash 2 12ms
ISI 1200ms
Flash 6 80msFlash 1
12ms
Channel 75 (Oz)
Stimulus Overlap
Two differing Inter Stimulus Interval’s (ISI) Clearly show Stimulus overlap problems
ISI 500 ms
Flash
P100
P200
P300
ISI 1200 ms
Flash
P100
P200P300
Areas for Potential Collaboration
• The Stimulus overlap Problem– ADJAR techniques
• Principal components analysis of ERP data
• Raw EEG and Spectral analysis– Something I am hoping to look at in relation to
Gamma activity in the future
Thanks…• Colorado State University
– Dr Bruce Draper, Dr Ross Beveridge (Computer Science)
– Carly Yadon, MS – Graduate Student in Psychology (Perceptual and Brain Science)
– Dan Lopez, MS – Graduate Student in Psychology (Perceptual and Brain Science) Erin Catallier/Jessa Hafer-Zdral (REU Students)
– Logan Keech (Undergraduate RA)
• University of California, San Diego– Dr Mike Pitts (Hillyard Lab)