A Novel, Countermeasure-proof, P300-Based Protocol for Detection of Concealed Information

A Novel, Countermeasure-proof, P300-Based Protocol for Detection of Concealed Information

J.Peter Rosenfeld, Michael Winograd, Elena Labkovsky, Ann Ming Lui

Department of PsychologyInstitute for NeuroscienceNorthwestern University

Previous P300 DD protocols used Separate Probe(P),Irrelevant(I) and Target(T) trials.

80% to 95% correct detection rates….but….

*Rosenfeld et al. (2004) and Mertens, Allen et al. (2007):These methods are vulnerable to Counter-measures (CMs)

via turning I’s into covert T’s.

Results from Rosenfeld et al. (2004): Farwell-Donchin paradigm(BAD and BCAD are 2 analysis methods.)Diagnoses of Guilty

Guilty Group Innocent Group CM Group

9/11(82%) 1/11(9%) 2/11(18%)

Amplitude Difference (BAD) method,p=.1

Cross-Correlation(BC-AD) Method, p=.1

6/11(54%) 0/11(0%) 6/11(54%)

Results (hit rates) from Rosenfeld et al. (2004): Rosenfeld paradigm

Week BAD* BC-AD*

1: no CM 12/13(.92) 9/13(.69)

2: CM 6/12(.50) 3/12(.25)

3: no CM 7/12(.58) 3/12(.25)

*Note: BCD and BAD are 2 kinds of analytic bootstrap procedures.

In the “Complex Trial Protocol,” P/I and T/NT decisions are separated:

Two stimuli per trial, 1.2-1.5 s apart. The first is P or I presented in white

font. The second is the same P or I

presented either in T color (green) or one of 4 non-T colors (red, yellow, etc.)

(The second could also be T and NT numbers, or whatever.)

4 STIMULUS TYPES

STIMULUS TYPE NUMBER PROBABILITY

Probe Target 30 .09 Probe non-Target 30 .09 Irrelevant Target 30 .09 Irrelevant non-Target 240 .73

All Probes 60 .18 Oddballs 90 .27

One probe and 4 irrelevants

P (T/P) = .5… vs… P (T/I) =.11 (Confound?)

DESIGN: as in ’04 paper, Exp. 2: 3 weeks in one group Week 1 Naïve Week 2 CM Week 3 Repeat Week 1 One block with one probe type, but

category varied and counterbalanced across subjects/weeks: 1)mother’s first names 2) family surnames 3) home towns

Main Study plus near replication. Innocent Control Group for FPs.

Countermeasures in Week 2: Also as in ’04 paper

Left finger press to Irrelevant # 1 Left toe wiggle to Irrelevant # 2 Right toe wiggle to Irrelevant # 3 Imagine Prof slaps you for Irrelevant#4 All these are done covertly so that

operator cannot detect them.

RTs (all stimuli). Replication like ‘04 study: no overlap.

P & I Individual RTs in CT Protocol (Flat liner at bottom did not beat test.)

Statistical tests within each subject:

T/F-tests comparing Week 1 RT or RT Variance versus Week 2 are all p<.01, and < .001 in the one subject who beat the test in Week 2.

Thus CM use is detectable.

In ’04 paper (old protocol), probe declines over weeks:

0 1 2 3 4WEEK

200

300

400

500

600

700

AM

PLI

TU

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, co

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IRRELEVTARGETPROBE

NEW RESULTS: P300s

P300, p-p

Two* possible (P-I) tests:

1)Traditional: Probe versus mean of all Irrelevants, P vs I-All.

2)Probe versus Maximum Irrelevant P vs I-max (“simple hit”) or Probe

versus I-max not associated with elevated RT (“RT-screened Hit”).* at .9 or .95 confidence levels.

Main Study. Within-subject correct detections of guilty subjects based on bootstrap comparison of probe P300 against the average of all irrelevant P300s over 3 weeks.

WEEK Hit Rate [Hit Rate] Week 1 (no CM): 11/12 (92%) [12/12*( 100%)] Week 2 (CM): 10/11 (91%) [11/12* (92%)] Week 3 (no CM): 11/12 (92%) [12/12* (100%)]

Main Study: False positive(FP) group. Confidence=.9 Confidence=.95 Test FPs Hits A’ FPs Hits A’ Iall .08 .92 .95 0 .92 .98 Imax 0 .92 .98 0 .92 .98

Main Study: Simple and RT-qualified diagnoses (at confidence = .9, Probe vs. Imax (or RT-qualified Imax) across 3 weeks (n values in parentheses). CM use also shown.

Week 1 (12) Week 2 (11) Week 3 (12)

Simple hits .92 .73 .92

Hits/RT qualified .92 .91 .92

CM use 0.0 1.0 0.0

Near Replication: Within-subject correct detections (“Hits”) of guilty subjects based on bootstrap comparison (at 2 confidence levels) of probe(P) P300 against the average of all irrelevant P300s (I-All) over weeks, and against the largest irrelevant P300 (I-Max).

CONFIDENCE LEVEL: 0.90 WEEK P vs I-All: Hits, [FPs], A’ P vs I-Max: Hits,

[FPs] A’ 1: 12/12 (100%),[8%] .91 11/12 ( 92%), [0%]

.98 2: 12/12 (100%) 11/12 ( 92%) * 3: 9/10 (90%) 7/10 (70%)

CONFIDENCE LEVEL: 0.95 WEEK P vs I-All: Hits, [FPs], A’ P vs I-Max: Hits, [FPs],

A’ 1: 11/12 (92%),[0%] .98 11/12 ( 92%), [0%] .98 2: 12/12 (100%) 11/12 ( 92%) * 3: 9/11 (82%) ** 8/11 (73%)**

CTP Mock Crime Study: Preliminary Results. Note Target= 11111. (Mike Winograd’s study)

Conclusions (& Why ? ) The complex trial protocol is CM-

resistant and accurate in the CIT Context.

*The S1 involves no classification or decision, unlike older protocols, whose target classification task is removed, leaving all resources devoted to probe/irrelevant recognition.

*CMs force more attention to first stimulus increased probe (& Irrel) P300s.

NEXT? We need to extend CTP to our

hybrid CQT screening protocol (Rosenfeld et al., 1991.)

We need to try 3-4 blocks a session, each with different probe category.

CTP should be even better with more Irrelevants.

A Novel, Countermeasure-proof, P300-Based Protocol for Detection of Deception (DD).

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A Novel, Countermeasure-proof, P300-Based Protocol for Detection of Concealed Information

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