Countermeasures%20to%20P300-based%20Guilty%20Knowledge%20Tests%20of%20Deception - PowerPoint PPT Presentation

Title: Countermeasures%20to%20P300-based%20Guilty%20Knowledge%20Tests%20of%20Deception


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Countermeasures to P300-based Guilty Knowledge
Tests of Deception

• J.Peter Rosenfeld, Matt Soskins,Joanna Blackburn,
  Ann Mary Robertson
• Northwestern University.
• Supported by DoDPI

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Some History (earliest publications)

• Rosenfeld et al., 1987,1988,1991
• Farwell and Donchin, 1991
• Allen, Iacono, Danielson, 1992
• Johnson and Rosenfeld, 1992
• Since we were there at beginning, why do we
  challenge now with countermeasures? (1) Its
  about time.

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2) Farwells web page, claiming 100 accuracy
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Stimuli

• Probes (P or R in figures) Items which subject
  is suspected of knowing (e.g., murder weapons).
  Subject denies(lies).
• Targets (TR) Items Items to which subject
  presses YES . (Benchmark P300).
• Irrelevants (I or W in figures) Items of which
  subject has no knowledge and denies, honestly, by
  pressing NO .

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How P300 amplitude is supposed to catch Liars
1)PgtI (BAD) 2)P-TR corr gtP-I corr(BC-AD)
1)PI 2)P-I corr gtP-TR corr
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Whither R-TR correlation if there are latency
differences?
Probe P3 Target P3
Nothing should happen to bootstrapped amplitude
difference test (BAD) but bootstrapped
cross-correlation test (BC-AD) should fail.
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Experiment 1, based on Farwell Donchin (1991)

• --6 Different Probes
• --Innocent, Guilty, and Countermeasure(CM) Groups
• --Countermeasure Associate various latent
  responses to different categories (jewelry type,
  drawer color, operation name, etc.), all
  irrelevant members of the category.
• --Off the Street subjects (Psych 101).

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General Instructions.

• Mock crime scenario
• Press Yes to Targets (on list)
• Press No to all other stimuli (Possibly guilty
  probes and Irrelevants).

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More simply.

• Probe Target I1 I2 I3 I4 ring
  bracelet necklace watch broach tiara
• red brown yellow purple red
  blue
• donkey tiger lion cow pig
  horse
• etc., etc... (only half the matrix
  here.)
• All these are shuffled, presented in random
  order, involving 4 repetitions of each item.

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What are the covert countermeasures for the 6
categories of 6 probes?

• 1) Jewelry category.micro right finger wiggle
• 2) drawer lining category. left
  
• 3) owners name category. toe
  
• 4) operation name category right
• 5) location of item category Imagine professor
  slaps you
• 6) desktop categoryDo Nothing
• I.e., make irrelevants into relevant targets.

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Guilty group Probe(R) gt Irrelevant (W).
R gt W
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Guilty Group TR vs R
Both have P300
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Innocent Group R vs W
Both lack P300
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Innocent Group TR vs R
TR towers over P (R)
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CM Group R vs W
No difference P(R) vs I (W)
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CM Group Tr vs R
Target gt Probe
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Results, Exp. 1 CM works, and analysis method
matters
Diagnoses of Guilty
Amplitude Difference (BAD) method,p.1
Innocent Group
Guilty Group
CM Group
9/11(82)
1/11(9)
2/11(18)
Cross-Correlation(BC-AD) Method, p.1
6/11(54)
0/11(0)
6/11(54)
--with Off the street subjects see next 2
slides.

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Guilty Subject, probe(R) vs irrelevant(W)
R gtgt W subject clearly guilty
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but clear latency shift in TR and R P300s
..so BC-AD fails, BAD catches the S.
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Do Reaction Times help?
CM Group
Guilty Group
9/10 90 BAD
3/10 30 BART
These are guilty calls based on
bootstrapped (Probe-Irrelevant) RTs, at p .05
.
Bootstrapped Analysis of RT difference, R-W.
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Absolute Irrel. RTs for CM and Inno. Groups
overlap.
..and 3 fastest CM-ers beat tes, 3 slowest did not
I.e., they dont help either.
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Experiment 2 The one probe protocol (Rosenfeld
et al., 1991).

• 100 simpler to conceptualize
• There are 6 items, repeated 30-40 times
  randomly, consisting of..
• A probe, subject maybe guilty,
• A target to force attention (not really necessary
  but allows us to test Farwell cross-correlation
  method vs. ours.)
• 4 irrelevants.

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Standard autobiographical oddball paradigm.

• 6 dates are presented, one is the birth date.
• 5 other dates with no personal significance, one
  is a target, four are irrelevant.
• Subject is feigning head injury, the inability
  to recognize birth date 50 of the time, so he
  presses yes and no to all dates on 50-50 basis.

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Design

• One group of advanced Ss run in 3 successive
  weeks. (Also Control group.)
• Week 1 All naïve(about CM) and guilty (of having
  birth date and recognizing it despite overt lies.
• Week 2 Use explicit countermeasure (to be
  explained).
• Week 3 Repeat first week, stop the CM.

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Whats the CM?

• When you see the first Irrelevant, do micro left
  finger wiggle.
• When you see second Irrelevant, do micro right
  toe wiggle.
• When you see third irrelevant, imagine me
  slapping your face.
• When you see fourth Irrelevant, do nothing.
• I.e., make irrels. into rel. targets.

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Results, week 1(guilty) Probe(R) vs.Irrelevant
(W)
As usual, RgtgtW
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Week 1 Probe(R) and Target(TR)
Both have nice P3
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Week 2 Explicit CM, R v W
Not so different anymore...
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Week 3 5/12 test beaters(effortless), R v W
Surprise! R W
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Week 3 5/12 test beaters, R v TR--classic
defeats
..and TR gtgt R as with innocents.
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Exp. 2 quantitative.

• WK BAD BC-AD BART
• no CM 12/13(.92) 9/13(.69) 8/13(.62)
• CM 6/12(.50) 3/12(.25) 0/12(0.0)
• no CM 7/12(.58) 3/12(.25) 5/12(.42)
• (Control group nothing much happened over 3
  weeks of repeating week 1.)

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RTs for 3 weeks week 1 week 3, proving CM not
used in week 3.
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Irrelevant RTs, with and without CM. No overlap!
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But in week 3, RT no help, as we saw...
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Overall amplitude effects...
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Conclusions, bottom lines..

• 6-probe protocol beat-able, RT is no help, and
  the 6 probe combination lacks a real rationale
  anyway. (Lykken wouldnt like?)
• 1-probe protocol may be explicitly beat-able, but
  the very slow Irrelevant RT distribution will
  raise suspicions. 1 probe per run is more
  Lykkenable.
• BUT---1-probe paradigm after CM practice is
  beat-able, period.

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What to do?

• We have found(submitted) that within individuals,
  the scaled scalp distribution method detects 73
  (not great) using statistical criteria yielding 0
  false positives.
• This method should be worked on, because there is
  no obvious CM as there is with simple amplitude.