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

Principal Collaborators Joel Ellwanger Tuti Reinhart Miller Archana Rao Matt Soskins Greg Bosh Many of the original ideas here were theirs.

A simple neural code

Event-related potentials

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

P300 at 3 scalp sites

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

Normals: autobiog. oddball

CHI patients: autobiog. oddball

Individual detection rates for various stimuli (normal simulators).

E-Name forgetters(oddball is dark line)

Screening example

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.

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.

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.)

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

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 >

Match-To-Sample example

Computer-plotted data:

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).”

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?

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

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

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

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% !!

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

FzCz Pz SITE AMP

Fz Cz Pz lie truth FzPz Cz SITES

Scaling: McCarthy & Wood (1985) recommend the vector length method. fz(s)=fz/[FZ^2+CZ^2+PZ^2] Some scaling is required to make the interpretation of differentially located neurogenerator neuron sets.

Match-to-Sample Test: advanced version 386 sample (*)

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)

ERPs in Liar Group to R and W

Deception swamps out R/W effect

“Profiles” of Deception

Truth vs Lie Groups

Deception overcomes paradigm effects

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?

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%).

Only lying liars stick out.

Same result with simple truth control

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

Psychopathy Effect is frontal,late(?)

What’s next? We have done pretty well with three(one)sites. The next step is to utilize 32 sites. This may adequately sample the head... But then, we may have too many sites to manage. So we will utilize principal component analysis in space to find what Donchin calls “virtual” sites. We also need to perfect within-subject analysis.

The data: FzCzPz AMP Are these curves parallel? “Normal” Distribution

Individual Profile Diagnostics: 1. Srebro,R. EEG Journal,Vol. 100,(1996) This is a cross correlation/bootstrap method. 2. Our present, to-be-explored method: –Bootstrap distributions of average P300 values for each site/condition point. –Do ANOVA to obtain condition(known truth and test)-by-site interaction value of F-statistic. See how this value fits into a distribution of Fs based on iterated, randomly shuffled truth and test values.

Individual Analysis Cross correlation takes care of scaling, so Srebro’s method is used for “pure” profile effects. For unscaled data, which confounds amplitude and distribution(but could possibly better discriminate truth-tellers and liars), we use the ANOVA method, particularly to see the F for interaction.

Site List 1. F7 6. T3 11. T5 2. F3 7. C3 12. P3 3. FZ 8. CZ 13. PZ 4. F4 9. C4 14. P4 5. F8 10. T4 15. T6

Different profiles(15 sites, one guilty subject), T and L blocks. Truth Li e r = +.17

Real vs shuffled z-scores Real Shuffled

Another guilty subject... Real Shuffled

Innocent Subject: Truth,Lie blocks have “identical” profiles r = =.91

---So the real(dark) z-values are within the shuffled distribution.

New Data: 30 sites We used paradigms of Rosenfeld et al., (1991), M. Johnson & Rosenfeld(1992). 4 accused items,4 irrelevants, one target/standard, “TAKING LIE TEST.” Accused items have high probabilty in subject population(pot use, cheating, plagiarism). Irrelevants have lower probability:(sell hard drugs, porn films).

Response to target item(LIE TEST) in 9 G vs 4 I Ss r = -.01

Target(LIE TEST) responses in Ss guilty of 1(9),3(3)items p(inter)<.001 r = -.01

Guilty Ss(n=13): Relevant vs Standard r = +.61 p(inter)>.2

Innocent Ss(n=7): Relevant vs Standard r = -.16 p(inter)<.02

Guilty Ss shown(n=13); p.5 (Also, main effect p<.05)

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--> “Old”(LR) or “New”(LW) –bed-- an actual memory word “Old” (M) –table-- a completely new word “New” (W)

Profiles depend on belief:

Replication data: almost ditto

P300 Latency is the unconscious recognizer

Replication data: ditto !

What’s next? What does Malingered “false” memory look like? Again, what happens as sites are added? ________________________________