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

  2. Principal Collaborators • Joel Ellwanger • 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. 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). • Matches to samples in tests of malingered cognitive deficits

  8. Normals: autobiog. oddball

  9. CHI patients: autobiog. oddball

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

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

  12. Screening example

  13. 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.

  14. 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.

  15. 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.)

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

  17. 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------------>

  18. Match-To-Sample example

  19. Computer-plotted data:

  20. 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).”

  21. 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?

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

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

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

  25. 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% !!

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

  27. SITE AMP Pz Fz Cz

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

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

  30. 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)

  31. ERPs in Liar Group to R and W

  32. Deception swamps out R/W effect

  33. “Profiles” of Deception

  34. Truth vs Lie Groups

  35. Deception overcomes paradigm effects

  36. Specificity (“Pinnochio”) • Simple Truth vs. Lie Groups differ in task demands. • This is not relevant for practical field detection. • It is relevant for claims pertaining to a specific lie response. • How do you make a “perfect” control group?

  37. An imperfect(but not bad) control Two groups run in two trial blocks of autobiog. oddball: [1. Phone #, 2. Bday] • Lie Group • Block 1 : Respond truthfully, repeat forwards. • Block 2: Lie 50% of time, repeat forwards. • Control Group • Block 1: Respond truthfully, repeat forwards. • Block 2: Respond truthfully, repeat backwards(50%).

  38. Only lying liars stick out.

  39. Same result with simple truth control

  40. Lie Response<>Truth Response; Psychopathy is irrelevant(swamped).

  41. Psychopathy Effect is frontal,late(?)

  42. False(honestly believed)memories: • Deese/Roediger paradigm • Presented words at study: sleep, bed, dream,blanket,pajamas,dark…. • Not presented word: night. • Test words: • night-- a critical LURE--> possible responses: “Old” or “New” • bed-- an actual memory word “Old” • table-- a completely new word “New”

  43. Profiles depend on belief:

  44. Replication data: almost ditto

  45. P300 Latency is the unconscious recognizer

  46. Replication data: ditto !

  47. What’s next? • What does Malingered “false” memory look like? • Again, what happens as sites are added? • ________________________________ • jp-rosenfeld@northwestern.edu