ERPs in Deception, Malingering, and False

Memory

J. Peter RosenfeldPsychology DepartmentNorthwestern University

Evanston Illinois,USA

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.

A simple neural code

Event-related potentials

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)

P300 at 3 scalp sites

We are always wanting to compare waves…

• ..that is, group or condition

• averages!

EVENT RELATED POTENTIAL AVERAGING…..

HERE IS WHAT SPONTANEOUS EEG LOOKS LIKE……

…..from 4 sites on the scalp:

HERE IS A SINGLE SWEEP …

HERE ARE 3 TRIALS….

REMINDER FOR PROF TO TAKE

the class to the movie…called, “ERP Averaging”

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.

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

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:

EACH SET OF 18 SINGLE SWEEPS IS AVERAGED YIELDING 6 AVERAGES…

….that look like real average of original set but with variations

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….

3-stimulus protocol

• 1probe

• 2 irrelevant

• 3 target

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

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------------>

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%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%

Another View of same effect:

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:

Fz Cz Pz

SITE

AMP

AMP

Fz

CzPz

lie

truth

Fz PzCz

SITES

Match-to-Sample Test: advanced version

• 386 sample• 212 • 457• 386 (*)• 789• 325• 123

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).

Problems with these simple oddball

methods…• (1) All the data I have shown --with

respect to scalp distribution-- were based on group analysis, whereas in deception detection, individual diagnosis is the key and we never did better than 73% accuracy, even with 32 electrodes!

• (2) Countermeasures…more later…

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”

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?

• ________________________________

• jp-rosenfeld@northwestern.edu