Post on 18-Dec-2015
transcript
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.
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)
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….
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.)
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------------>
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?
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:
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)
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%).
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”