ERPs in Deception, Malingering, and False Memory

1. ERPs in Deception, Malingering, and False Memory J. Peter Rosenfeld Psychology Department Northwestern University Evanston Illinois,USA

2. Principal Collaborators to 2008: • Joel Ellwanger Ming Lui • Tuti Reinhart Miller • Archana Rao • Matt Soskins • Greg Bosh • Many of the original ideas here were theirs.

3. A simple neural code

4. Event-related potentials

5. P300 Attributes: • An Endogenous, Event-Related Potential (ERP) • Positive polarity (down in Illinois). • Latency range: 300-1000 msec • varies with stimulus complexity/evaluation time • Typical Scalp Amplitude(Amp) Map • Pz > Cz > Fz • Amp = f(stim. probability, meaning)

6. P300 at 3 scalp sites

7. We are always wanting to compare waves… • ..that is, group or condition • averages!

8. Event Related Potential Averaging…..

9. …..from 4 sites on the scalp: Here is what spontaneous EEG looks like……

12. Here is a single sweep …

15. Here are 3 trials….

18. the class to the movie…called, “ERP Averaging” Reminder for prof to take

19. Since averages are so much cleaner than single sweeps, …and show the true stimulus-evoked event that is time-locked to the eliciting event, and are more noise free, ….it obviously makes sense to compare averages rather than single sweeps, that is, to do analysis, like t-tests on averages. People did that in comparing group ERPs or grand averages.

20. For example, • The schizophrenic group average versus the normal average • or the well-trained group average P300 vs. that of the untrained group. • Remember, in a group, each subject has an average ERP. • ….but within a single subject, there are only single sweeps to compare

21. In Bootstrapping… • …..the original set of single sweeps is repeatedly randomly sampled –but with replacement— …yielding multiple averages in a single subject. • Let’s say there are 6 repetitions of sampling of 18 single sweeps:

22. ….that look like real average of original set but with variations Each set of 18 single sweeps is averaged yielding 6 averages…

24. P300 amplitude as recognition index • Autobiographical items (previous slide) • Guilty Knowledge test items (Rosenfeld et al., 1988) • Antisocial/illegal acts in employee screening (Rosenfeld et al., 1991). • Tests of malingered cognitive deficits with oddball paradigm. Do folks recognize personal info? Start with normal models….

25. 3-stimulus protocol • 1probe • 2 irrelevant • 3 target

26. Normals: autobiog. oddball

27. CHI patients: autobiog. oddball

28. Individual detection rates for various stimuli (normal simulators).

29. E-Name forgetters(oddball is dark line)

30. Screening example

31. Autobiographical paradigm has limitations in detecting malingerers • Most malingerers are not so unsophisticated as to verbally state that they don’t recall, say, their birthdate, when in fact they may have just filled out a card in which they provided that information.

32. Continuation… • The behavioral “MDMT” was developed as an entrapment test to catch these people. It’s a simple matching-to-sample test: A sample 3-digit number is presented followed either by a match or mismatch.

33. Simple MDMT paradigm: • There is a 5-15 second interval between sample and probe. This is an easy task, yielding 100% performance even in patients with moderate head injury--unless, oddly enough, they happen to be in litigation ! • Where does one set the threshold for diagnosis of malingering? 90%? (Some non-litigating malingerers score well below 90%, as we’ll see.)

34. Behavioral MDMT not reliable: Some non-litigating pts. fail

35. P300-Souped-up MDMT: simple version • “Simple” means only one probe stimulus per sample. • P300 is recorded as soon as the probe --match or mismatch-- is presented. • Match probability is kept low. • RESULTS------------>

36. Match-To-Sample example

37. Computer-plotted data:

38. What would 75%-HITTING plaintiff’s lawyer say? • “Sure, my client scores 75% correct and his P300 to matches is bigger than to mismatches. But that’s because he mostly DOES make the correct discrimination--but 75% is still less than normal. Therefore, give us the money (me, one-third).”

39. Continuation… • We did 2 experiments: 1) If a malingerer aims to score 75% correct, whither P300? 2) What happens to P300 with a really tough discrimination?

40. Manipulated 75% “hit” rate produces a larger P300…. 100% 100%

41. Experiment 2: Difficult tasks: 7 and 9 digit numbers, match to sample.

42. P300 wiped out in difficult task, at 75%, even at accuracy> 90%

43. Another View of same effect:

44. Simple P3-MDMT summary: • If one fakes 75% hits, one’s P300 gets bigger(or doesn’t change). • If one has genuine difficulty--honest 75%--then P300 is totally removed. • These findings should allow discrimination of normals, malingerers, real deficit(pts). • BUT…diagnostic hit rate only 70% !!

45. Scalp Distribution • For P300, Pz > Cz > Fz, usually, but… • There are many ways that this can be so:

46. SITE AMP Pz Fz Cz

47. Cz Pz Fz lie SITES truth AMP Fz Pz Cz

48. Match-to-Sample Test: advanced version • 386 sample • 212 • 457 • 386 (*) • 789 • 325 • 123

49. Stimulus-Response Types • Match(R) probe • “Match” (RR--honest/correct) • “Mismatch” (RW--dishonest/error) • Mismatch(W) probe • “Mismatch” (WW--honest/correct) • “Match” (WR--dishonest/error)

50. ERPs in Liar Group to R and W