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EDA reaction (from another thread)

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Author Topic: EDA reaction (from another thread)
posted 12-13-2007 01:10 PM Click Here to See the Profile for ebvan Click Here to Email ebvan Edit/Delete Message
I am convinced that EDA reactions, have less to do sweat than they do acetylcholine. I've been using a great EDA from limestone that works well with everyone except those taking boatloads of meds. It works with concrete workers and brick-layers - who's skin is dried out and leathery and whose eccrine sweat pores are quite damaged from whatever makes concrete and mortar work. All it takes is a wet-gel sticky electrode or some potassium chloride on the brass finger plates (my favorite - obtained from Axciton some years ago).

Acetylcholine is the enervating neurotransmitter in the sympathetic neurons in the skin, and is the same enervating neurotransmitter in the sympathetic neurons in the prefrontal cortex (the part of the brain responsible for attention, concentration, choice, judgement, complex problem solving, some aspects of personality, and all the mental gymnastics that go with lying or concealing information.)

Now guess why distraction, ADHD, singing songs, and outside stimulus affect the EDA. And guess why the test works with silent-answer and yes-answer series.

Our polygraph gear cannot distinguish between DRs and ORs. We have to conduct the exam and present the stimulus in a manner that we are confident that observed reactions are most likely DRs to the RQs stimulus - compared with DRs to the CQs.

My Question,
Based on this observation, What significance would you attach to a test, or what further questions would need to be resolved if you were to collect a chart series where
#1 the only significant reactions occurred in the EDA channel?
#2 EDA tracings appeared contradictory to the pneumo and/or cardio channels? ie strong reaction in pneumo and cardio and flat EDA to an RQ and flat pneumo and cardio and strong EDA reaction to an ajacent CQ.

Ex scientia veritas

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posted 12-13-2007 03:41 PM Click Here to See the Profile for rnelson Click Here to Email rnelson Edit/Delete Message
Answer to #2 is easy.

Training is generally (always) just add up the numbers for each spot.

I'd like to see that change, and I'll explain more in a bit. Krapohl (1999) demonstrated that doubling EDA scores can reduce inconclusives, without concerns for increased errors. OSS-3, and probably all other computer scoring models weight the EDA more heavily than the other components.


Answer to #1 is not so simple.

First, why is the EDA the only channel with reactions. Health? Medications? Movement or behavior artifacts?

Is your subject really a fit or suitable subject for the polygraph technique? Or, is a marginal candidate, for whom we should be unwilling to provide an unqualified opinion (i.e, without some form of CYA explanation that says "don't even think about arguing the validity of the test results in court.") Just look at the Deskovic mess at anti.

Both hand-scoring and computer scoring models are non-robust against bad data. Bad means not just messy, but unresponsive.

A test of this type might take care of itself, with weak numbers that produce inconclusive results.

Let pretend its meds, and your guy is a garden-variety sex offenders with depression, diabetes, high blood pressure, and allergies. That should give us a good combination of cholinergic, sympathomimetic, and adrenergic effects to goof with our data.

How confident will you be in the results? Would you say he's a fit subject?
Would you test him?

Depending on why, I mikght test him. But I'd also call him a marginal subject, and I'd qualify the results by listing his meds and diagnoses, and describing the quality of the test data.

Hand scoring systems often involve the use of ratios for assigning points, 2:1, 3:1 and so on. Handler and Krapohl showed that there is greater diagnosticity extant in smaller reaction differences, and we all know that the search for larger reaction difference is wishful thinking.

We also have the venerable Bigger-is-better, which I believe DACA describes for both 3 and 7 position systems. (correct me I am an wrong on that.)

One could argue that the 3 position system is theoretically more robust in its application, in that it relies primarily on the bigger is better rule, and makes no assumptions about the linearity of the data - which is important in consideration of the interfering influence of the handfuls of meds some clients take, and is equally important in consideration of the fact that the various polygraph equipment manufacturers have provided us with field equipment that often has unknown linearity.

We still wonder though how much bigger matters, and at what point to small differences become excessively noisy and unreliable.

So I took the time to study the bigger is better situation with some ROC plots.

This is the end result, and the plots illustrate the results with the OSS-3 training set N=292 for each of the components, used alone, using a ratio of 1.1:1. Below that level they get quite noisy.

ROC AOCs are

Pneumo = .75
EDA = .95
Cardio = .77

1.1:1 means that if you can see a difference and could argue that one bump is bigger than another, you can probably score it reliably.

While the cardio and pneumo look close, other experiments reveal roughly twice as much variability in pneumo data compared with cardio data.

That .95 for EDA is impressive and suggests that the EDA alone might be a potent diagnostic indicator. It is tempting to want to discard the other components but our data suggest the polygraph is better with the cardio and the pneumo components. But this strong AOC value helps us understand why it improves the results when we weight the EDA values as more important than the others.


Now wouldn't it be great if there were a very simple way of putting these pieces together in efficient field practices, that is easily understood and provides good interrater reliability.



"Gentlemen, you can't fight in here. This is the war room."
--(Stanley Kubrick/Peter Sellers - Dr. Strangelove, 1964)

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