all slides © s. j. luck, except as indicated in the notes sections of individual slides slides may...
TRANSCRIPT
All slides © S. J. Luck, except as indicated in the notes sections of individual slidesSlides may be used for nonprofit educational purposes if this copyright notice is included, except as noted
Permission must be obtained from the copyright holder(s) for any other use
The ERP Boot Camp
Isolating Components with Difference Waves
and The Boot Camp
Experiment
w1,1
w2,1
w3,1
w1,2w2,2
w3,2
w1,3
w2,3
w3,3
C1
C2
C3
E1
Difference Waves
C1 C2
C3E2
E1
E3
If a single component varies across conditions, it can be isolated by means of a difference wave
For this to work, the conditions must be so similar that only one component varies across conditions
E2
E3
Isolating the LRP
Left Hemisphere(Ipsi)
Right Hemisphere(Contra)
Right Hemisphere(Ipsi)
Left Hemisphere(Contra)
LRP = Contra minus ipsi, averaged over left & right hands
Smulders & Miller (2010)
Isolating the LRP
LRP = Contra minus ipsi, averaged over left & right hands
Smulders & Miller (2010)
Isolating the LRP
Left Hemisphere(Ipsi)
Right Hemisphere(Contra)
Right Hemisphere(Ipsi)
Left Hemisphere(Contra)
Nonlateralized components eliminated by subtraction
Smulders & Miller (2010)
Isolating the LRP
Left Hemisphere(Ipsi)
Right Hemisphere(Contra)
Right Hemisphere(Ipsi)
Left Hemisphere(Contra)
Overall hemisphere differences eliminated by subtraction(RHem more positive than LHem for both hands)
Isolating the LRP
Left Hemisphere(Ipsi)
Right Hemisphere(Contra)
Right Hemisphere(Ipsi)
Left Hemisphere(Contra)
Overall hand differences eliminated by subtraction(RHand more positive than LHand for both hemispheres)
Smulders & Miller (2010)
Isolating the LRP
LRP provides a pure measure of the relative activation of correct vs incorrect response at
each moment in timeSmulders & Miller (2010)
The C1 Wave
Mangun, Hillyard, & Luck (1993)
C1 can be isolated with Upper minus Lower difference wave
Isolating the P3 Wave• P3 amplitude depends on the probability of a task-defined
stimulus category, not the probability of a physical stimulus• P3 probability effect cannot begin until after categorization
occurs• Rare-minus-frequent difference wave isolates processes that
occur after perception and categorization• P3 latency indexes “stimulus evaluation time”
Shortcomings of Difference Waves
• May not isolate a single component- Example: Rare-Frequent yields P2, N2, P3
• If Cond1–Cond2 difference wave is reduced, cannot distinguish between smaller Cond1 and larger Cond2- For most components, need to look at original waveforms
as well as difference waves (not for N2pc/LRP)- Ask Emily how we solved this problem for LRP
• Changes in latency between Cond1 and Cond2 produce an apparent difference in amplitude- Not a problem if you view difference wave as simply
meaning a difference in the time course of amplitude
The MONSTER Paradigm
• Goal- Efficiently measure the speed and integrity of a broad set of specific neurocognitive processes- First step in determining the nature of deficits in a given
patient group- Possibly useful for diagnosis of disease subtypes (e.g., in
multiple sclerosis)
• Use orthogonal subtractions to isolate specific ERP components that reflect well-characterized neurocognitive processes- Same data divided different ways to isolate different
components
Stimuli and Task
Task: Attend to black or whitePress left for A (p = .80 or p = .20)Press right for B (p = .20 or p = .80)Left/Right and .80/.20 are counterbalanced
Stim: Duration = 200 msSOA = 1500 ± 150 ms2 blocks of 512 stimuli
Stimuli and Task
C1: Upper Checks minus Lower Checks
N2pc: Contra target minus Ipsi target
P3: Rare minus Frequent
LRP: Contra to response hand minus Ipsi to response hand
These subtractions are orthogonal -- same 1024 trials divided into different pairs of subsets and then subtracted
Recording with Biosemi ActiveTwo• Active Electrodes-
- Each electrode has a small, built-in preamplifier connected to an Ag/AgCl tip
- Doesn’t actually amplify; creates an ultra low impedance signal that is noise resistant
- Down side: Expensive to buy and replace- Fill electrode holders with gel and plug in electrodes- Flat electrodes for mastoids, eyes, etc.
Recording with Biosemi ActiveTwo
• Single-Ended (not differential) recording- Record electrical potential between “active” and CMS
(“common mode sense” -- analogous to ground)- Reference digitally, off line
• DRL (“driven right leg”) electrode- Think of it as a power source for the other electrodes
• High impedance• Digitization
- Separate A/D converter for each electrode- Output is fiber optic cable, which connects to a box near
the computer (safe, not an antenna for line noise)- Sampling rate = 1024 Hz (must be power of 2)- Built-in hardware low-pass anti-aliasing filter- No high-pass filter (DC recording)