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The ERP Boot Camp. Examples of Experimental Design. Example 1: The Attentional Blink. T2 Detection Accuracy. Raymond, Shapiro, & Arnell (1992). What Causes the Blink?. Are subjects unable to perceive T2 during the AB? Or do they see it and fail to remember it?

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the erp boot camp

The ERP Boot Camp

Examples of Experimental Design

example 1 the attentional blink
Example 1: The Attentional Blink

T2 Detection Accuracy

Raymond, Shapiro, & Arnell (1992)

what causes the blink
What Causes the Blink?
  • Are subjects unable to perceive T2 during the AB?
    • Or do they see it and fail to remember it?
  • Previous research shows that we can perceive even complex pictures at 8/sec
    • We ought to be able to perceive letters at 10/sec
  • Logic of study
    • Early sensory suppression during AB (P1 & N1)?
    • Late perceptual suppression during AB (N400)?
    • Postperceptual working memory suppression (P3)?
experiment 1 p1 and n1
Experiment 1: P1 and N1

T1 Task: Digit Odd or Even?

T2 Task: Red item Vowel or Consonant?

Prediction: No P1/N1 suppression during AB

experiment 1 results1
Experiment 1 Results

Difficult to draw strong conclusions from the lack of an ERP effect

experiment 2 n400
Experiment 2: N400
  • How to demonstrate that T2 was fully identified?
    • Show that it can elicit an N400

Sweet …. Sugar

Hot …. Sugar

  • If a semantic mismatch is detected when T2 is a word, then T2 must have been fully identified
experiment 2 results1
Experiment 2 Results

Does it matter whether this is really an N400?

Strategy 8: Use a component to study the processes that precede it rather than the process that generates it

experiment 3 control
Experiment 3: Control

Is N400 sensitive to modest changes in perceptibility?

Does even a slight perceived mismatch cause a large N400?

experiment 4 p3
Experiment 4: P3

Isolate P3 by subtracting frequent T2 from rare T2

experiment 4 results1
Experiment 4 Results

Does it matter whether this is really a P3?

recap of strategies
Recap of Strategies

Strategy #1- Focus on a specific component

Strategy #2- Use well-studied experimental manipulations

Strategy #3- Focus on large components

Strategy #4- Isolate components with difference waves

Strategy #5- Focus on components that are easily isolated

Strategy #6- Use component-independent experimental designs

Strategy #7- Hijack useful components from other domains

Strategy #8- Use a component to assess the processes that came before it

additional rules
Additional Rules

Rule #11- Never assume that the amplitude and latency of an ERP component are linearly or even monotonically related to the quality and timing of a cognitive process. This can be tested, but it should not be assumed.

Rule #12- Don’t forget about behavior in ERP experiments. Dissociations between behavior and ERPs are sometimes troubling, but they are often informative

example 2 schizophrenia
Example 2: Schizophrenia
  • Typical schizophrenia ERP task- Auditory oddball
    • 80-90% standards of one pitch
    • 10-20% targets of another pitch (count or press for targets)
    • Measure amplitude of P3 peak for rare stimuli
  • Large, replicable reduction in P3 amplitude (d = 0.89)
  • But what does it mean?

Mathalon et al., 2000

p3 latency in schizophrenia
P3 Latency in Schizophrenia
  • RTs are typically 100-200 ms greater in SC patients
    • RTs often not reported in P3 studies (most use a counting task in which RT does not apply)
  • P3 latency modestly greater in patients
    • Often not significant
  • Interesting: RT slowing + no substantial P3 slowing

Mathalon et al., 2000

a different approach
A Different Approach
  • The hardest part of ERP research is isolating specific components
    • This is why we don’t have a very good theory of the P3 wave
    • Makes it hard to interpret a reduction in patient P3 amplitude
  • Relevant strategies:
    • Isolate components with difference waves
    • Focus on components that are easily isolated
    • Use component-independent experimental designs
    • Use a component to measure the processes that necessarily precede it (focus on onset latency)
  • Additional strategy:
    • Take advantage of temporal resolution
    • Effect size = number of milliseconds!!!
subtraction approach
Subtraction Approach




Early Visual Processes

Upper minus Lower


Shifts of Attention

Contra Target minus Ipsi Target


Stimulus Categorization

Luck et al., 2006

Rare minus Frequent


Stim/Resp Translation

Contra Hand minus Ipsi Hand


Response Execution


p3 and lrp
P3 and LRP

(with Jim Gold, Becky Fuller, Emily Kappenman)

  • N2pc is not delayed in schizophrenia
  • Prior studies find little or no P3 delay
  • But RT is typically delayed by 100+ ms
  • Then what is delayed?
    • Stimulus/response translation (response selection)?
    • Response initiation and execution?
  • To test, examine P3, LRP, and RT
p3 latency
P3 Latency
  • P3 amplitude depends on the probability of a task-defined stimulus category
  • P3 effect cannot occur until after categorization
  • P3 latency is tied to the amount of time required to perceive and categorize a stimulus (“stimulus evaluation time”)
lateralized readiness potential lrp
Lateralized Readiness Potential (LRP)
  • More negative over contralateral cortex for hand movements
  • LRP cannot be elicited until stimulus/response translation (response selection) has occurred
  • But prior to completion of response programming

Miller & Hackley (1992)




Digit / Letter

p = .80/.20 or p = .50/.50

Left Hand / Right Hand

Duration = 200 ms

SOA = 1500±150 ms

Isolate P3 with Rare-minus-Frequent difference wave

Isolate LRP with Contra-minus-Ipsi difference wave

raw erp waveforms
Raw ERP Waveforms

Parietal Electrode Sites

Control RT

Patient RT







P3 amplitude difference for all probability levels

No P3 latency difference

p3 rare minus frequent
P3: Rare Minus Frequent

Parietal Electrode Sites

No P3 amplitude difference

No P3 latency difference

No slowing of simple perception & categorization

Difficult to know if this replicates previous research

response locked p3
Response-Locked P3
  • StimulusP3 not delayed
  • StimulusResponse is delayed
  • Prediction: P3Response should be delayed

Parietal Electrode Sites

Significant P3 onset latency difference

lrp contra minus ipsi
LRP: Contra Minus Ipsi

C3/C4 Electrode Sites

Significant amplitude difference

Significant onset latency difference

Significant amplitude difference

Marginally significant onset latency difference

schizophrenia summary
Schizophrenia Summary
  • Visual attention is normal
    • No increase in N2pc latency
  • Categorization is normal
    • No reduction in rare-minus-frequent amplitude
    • No increase in time from stimulus to P3 onset or peak
    • Increase in time from P3 onset to response
  • Response selection is impaired
    • Substantial reduction of LRP amplitude
    • Increase in time from stimulus to LRP onset
    • Possible increase in time from LRP onset to response