Presentation is loading. Please wait.

Presentation is loading. Please wait.

J. Peter Rosenfeld, John Meixner, Michael Winograd, Elena Labkovsky, Alex Haynes, Northwestern University.

Similar presentations

Presentation on theme: "J. Peter Rosenfeld, John Meixner, Michael Winograd, Elena Labkovsky, Alex Haynes, Northwestern University."— Presentation transcript:

1 J. Peter Rosenfeld, John Meixner, Michael Winograd, Elena Labkovsky, Alex Haynes, Northwestern University

2 AKAGuilty Knowledge Test. Physiological responses accompany recognition of information known only by guilty perps and authorities. Responses are traditionally Autonomic –HR, GSRbut we use brain waves:



5 An Endogenous, Event-Related Potential (ERP) Positive polarity (down in Illinois). Amp = f(1/[stim. Probability], meaningfulness )


7 PROBE: GUILTY KNOWLEDGE ITEM: $5000 Press non-target button. IRRELEVANT: OTHER AMOUNT: $200 Press non-target button. TARGET: OTHER AMOUNT: $3000 Press target button.

8 80% to 95% correct detection rates….but…. *Rosenfeld et al. (2004) and Mertens, Allen et al. (2008):These methods are vulnerable to Counter-measures (CMs) via turning Is into covert Ts.

9 When you see a specific irrelevant, SECRETLY make some specific response, mental/physical. After all, if you can make special response to TARGET on instruction from operator, you can secretly instruct yourself. Irrelevant becomes secret target. It makes big P300. If P = I, no diagnosis.

10 2 tasks for each trial: 1. implicit probe recognition vs. 2. explicit Target/Non-Target discrimination Hypothesized Result: Mutual Interference of 2 tasks more task demand reduced P300 to P. CMs hurt Old test.

11 Farwells web page, claiming 100% accuracy: Farwells web page, claiming 100% accuracy:

12 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 %)

13 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: BC-AD and BAD are 2 kinds of analytic bootstrap procedures.



16 2 stimuli, separated by about 1 s, per trial, S1; Either P or I…..then…..S2 ; either T or NT. *There is no conflicting discrimination task when P is presented, so P300 to probe is expected to be as large as possible due to Ps salience, which should lead to good detection; 90-100 % in Rosenfeld et al.(2008) with autobiographical information. It is also CM resistant. (Delayed T/NT still holds attention.) * I saw it response to S1. RT indexes CM use.

17 WEEK Hit Rate Week 1 (no CM): 11/12 (92%) Week 2 (CM): 10/11 (91%) Week 3 (no CM): 11/12 (92%)

18 3 groups (n=12) Simple Guilty (SG), Countermeasure (CM), Innocent Control (IC) All subjects first participated in a baseline reaction time (RT) test in which they chose a playing card. SG and CM subjects then committed a mock crime. Subjects stole a ring out of an envelope in a professors mailbox. All subjects were then tested for knowledge of the item that was stolen. There were 1 P (the ring) and 6 I( necklace,watch,etc). CM subjects executed covert assigned responses to irrelevant stimuli in an attempt to evoke P300s to these stimuli to try and beat the Probe vs. Irrelevant P300 comparison.



21 Condition Detections Percentage SG 10/12 83 CM 12/12 100 IC 1/12 8


23 Unlike 3-SP, the CTP is highly sensitive at detecting incidentally acquired concealed knowledge in a mock-crime (as with autobiographical knowledge). Another advantage of the CTP vs 3-SP or polygraph CIT: resistance to CM use. CM use produces a large increase in RT between the baseline and test block, and within test block, probe vs irrelevant RT.

24 5-button I SAW it box. The subject is instructed to press, at random *, one of the 5 buttons. We hoped that this would make CMs harder to do. It didnt, but we caught the CM users anyway.

25 Autobiographical information (birthdates): One P and 4 I (other, non-meaningful dates). 3 Groups as before: SG,CM, IC. NEW : mental CMs to only 2 of the 4 Irrelevants: Say to yourself your first name OR your last name. These are assigned prior to run. Only one block per group (no baseline).


27 Group BT/Iall.9 BT/Imax.9 SG 13/13 (100%) 13/13 (100%) IC 1/13 (7.6%) 1/13 (7.6%) CM 12/12 (100%) 10/12 (83%) RT still nicely represents CM use within a block.



30 Rosenfeld & Labkovsky



33 John Meixner & Peter Rosenfeld How do you catch bad guys before crimes are committed, and before you know what was done, where, when?

34 +Experimental guilty subjects come to lab and study 3 brochures dealing with pros & cons of 1) What CITY to attack, 2) What METHOD to use, 3) What DATE to attack on for later 3 blocks of CTP tests. + Then they write letter to boss with recommendations. + Innocent controls study vacation brochures, write recommendation letter to parents/room- mates.


36 A Mock Terrorism Application of the P300-based Concealed Information Test Department of Psychology, Northwestern University, Evanston, IL

37 IallImaxBlind Imax GuiltyInnocentGuiltyInnocentGuiltyInnocent 1000648985287985603 1000610999416998602 955598889476892649 996611898430893605 99415094617943689 909475698284761547 945600677365702536 997555959250961569 999586908217907565 985 690 888 382886706 912390 667 129698650 903644 837 215842702 966546863289872619 12/120/1212/120/1210/120/12 AUC = 1.0 AUC =.979 Table 1. Individual bootstrap detection rates. Numbers indicate the average number of iterations (across all three blocks) of the bootstrap process in which probe was greater than Iall or Imax. Blind Imax numbers indicate the average number of iterations in which the largest single item (probe or irrelevant) was greater than the second largest single item. Mean values for each column are displayed in bold above detection rates.

38 CTP is a promising, powerful paradigm, against any number of CMs, mental and/or physical and RT reliably indicates CM use. The new P900 might also.

39 Instead of CM first, then I saw it response… Do them simultaneously! Then Bye Bye RT index:

40 Probe Iall




Download ppt "J. Peter Rosenfeld, John Meixner, Michael Winograd, Elena Labkovsky, Alex Haynes, Northwestern University."

Similar presentations

Ads by Google