The ERP Boot Camp

1. The ERP Boot Camp Examples of Experimental Design

2. Example 1: The Attentional Blink T2 Detection Accuracy Raymond, Shapiro, & Arnell (1992)

3. 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)?

4. 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

5. Overlap Problem

6. Experiment 1 Results

7. Experiment 1 Results Difficult to draw strong conclusions from the lack of an ERP effect

8. 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

9. Experiment 2: N400

10. The Overlap Problem

11. Experiment 2 Results

12. 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

13. Experiment 3: Control Is N400 sensitive to modest changes in perceptibility? Does even a slight perceived mismatch cause a large N400?

14. Experiment 4: P3 Isolate P3 by subtracting frequent T2 from rare T2

15. Experiment 4 Results

16. Experiment 4 Results Does it matter whether this is really a P3?

17. 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

18. 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

19. 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

20. 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

21. 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!!!

22. Subtraction Approach STAGE SUBTRACTION COMPONENT Early Visual Processes Upper minus Lower C1 Shifts of Attention Contra Target minus Ipsi Target N2pc Stimulus Categorization Luck et al., 2006 Rare minus Frequent P3 Stim/Resp Translation Contra Hand minus Ipsi Hand LRP Response Execution RT

23. 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

24. 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”)

25. 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)

26. Methods 3 3 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

27. Raw ERP Waveforms Parietal Electrode Sites Control RT Patient RT 486 557 643 734 576 648 P3 amplitude difference for all probability levels No P3 latency difference

28. 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

29. 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

30. LRP: Contra Minus Ipsi C3/C4 Electrode Sites Significant amplitude difference Significant onset latency difference Significant amplitude difference Marginally significant onset latency difference

31. 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