Electroencephalogram (EEG) and Event Related Potentials (ERP)

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Electroencephalogram (EEG) and Event Related
Potentials (ERP)

• Lucy J. Troup
• 28th January 2008
• CSU Symposium on Imaging

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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

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What are Event-Related Potentials?

• 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 20-50?v / ERP 1-10 ?v

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• Time-locking Signal/Noise Ratio Reduction
• ERP derived from EEG

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Where do potentials come from?

• Not action potentials
• ExcitatoryPostSynapticPotentials
• InhibitoryPostSynapticPotentials
• Most likely source

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How do we analyze ERP waves?

• 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

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Classic Approaches to Analysis

• Parametric Statistical comparisions
• Peak to Peak
• Mean Amplitude
• Peak Latency
• Covariation
• PCA
• Source Localization
• BESA

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Well-studied ERP components

• Visual
• C1, P1, N1, N170
• Auditory
• BER, N1, MMN
• Cognitive
• N2b, N2pc, P3, N400, ERN, FRN, RP, LRP

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ERP precautions

• Cant determine Where, only When
• Scalp Topography vs Source Analysis
• Doesnt measure all neural activity
• Closed vs Open Fields
• Can only use when time-locking is practical
• Not applicable for all areas of psychology

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Some potential problems

• 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)

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What information does a component provide for
us?

• Example from Troup, Pitts, Draper Catellier
  (2007)

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Electrical Geodesics Inc. 128 channel high
density EEG
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Experiment 1

• N19
• Raw and Gabor Faces
• Presented randomly
• 3 blocks of 66 faces

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Experiment 2

• N19
• 7 Blocks 80 pairs per block
• Ss respond with key press to Same Face pairs

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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?

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Scalp Location Frontal Left Temporal Right
Temporal Central Center Occipital
Behavioral Response Same Correct Different
Correct Same Incorrect
Stimulus type Raw Gabor
Amplitude and Latency
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Same/Different Grand Average Data
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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?

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Stimulus Overlap

• Two differing Inter Stimulus Intervals (ISI)
  Clearly show Stimulus overlap problems

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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

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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)