Freethought & Rationalism Archive

Rev. Joshua · 08-12-2002, 07:52 AM

When I first started training in interrogation, one of the fundamental rules we learned is that the only way to catch someone in a lie was to compare their statement to a known fact. Anything else: polygraphs, voice-stress analysis, neurolinguistics, etc. falls into the category of "indicators of deception." I never said, "I think so-and-so is lying" (except to them, in an attempt to get them to tell the truth). I simply said, "I saw several indicators of deception."

For many people, galvonic skin response, accelerated heart rate, etc. can be indicators of deception; but that information is worthless without additional investigative data.

Joshua

Kachana · 08-12-2002, 06:20 PM

Quote:

Originally posted by emphryio:
<strong>To Kachana
What if two sons were present at the computer at the time the site was up? Mikey is looking at it taking notes. Johnny is standing behind thinking that Dad would be mad if he knew what his sons were looking at and saying, "Mikey don't look at that. We'll get in trouble."

Dad questions Mikey but he's an accomplished liar. Meanwhile innocent bystander Johnny gives the "guilty" response.

So a lie detector can be worse than insulting to a person's intelligence. It can wrongfully accuse someone of wrongdoing. (The links Lone Ranger gave have examples of this.)</strong>

Sure, your point is valid. However, to carry this example over to a real crime (not a household where there are only a few suspects that know each other) a 'guilty' response would at least suggest knowledge of some kind that could be useful for further questioning. And in real life, it is less likely than in the example you gave - given the larger and more diverse population - that someone arrested for the crime would give the guity response due to knowing the real culprit but being innocent.

I put guilty in quote marks as I don't think such tests should be interpreted as evidence of guilt, for reasons such as the one you gave and others (e.g. someone may coincidentally own the same baseball hat in my first example, another random variable such as an illness or an extraneous sound could cause the 'guilty' response at the vital moment). I think that such tests have potential as a type of tool to help authorities decide which people to question/ focus on and which leads to follow up, but it makes me nervous thining of them being shown to juries as evidence.

Kachana · 08-12-2002, 06:48 PM

Quote:

Originally posted by emphryio:
<strong>
David Lykken, emeritus professor of psychology at the University of Minnesota, is a leading critic of polygraphs and author of an influential book, "A Tremor in the Blood" (1981). He can hardly believe he still has to tell people that the polygraph isn't science.

"There's something about us Americans that makes us believe in the myth of the lie detector. It's as much of a myth as the Tooth Fairy," he exclaims in frustration.

]</strong>

Emphyrio, a distinction needs to be made between different types of polygraphic tests. Some types may be unreliable and founded on shaky theory yes, but that doesn't negate the potential validity of other forms.

As you have quoted (and I assume give credence to the opinion of) David Lykken, who better to quote in this matter than the man himself!

David Lykken (from 'Detection of guilty knowledge: A comment on Forman and McCauley.' Journal-of-Applied-Psychology. 1988 May; Vol 73(2): 303-304.):

Forensic polygraphers do not use the theoretically more sound method of guilty knowledge detection, in the belief that appropriate GKT items could not be designed in the field situation. I argue that this assumption is unfounded and that what is potentially one of the most accurate and socially useful of psychological tests is being arbitrarily neglected.

Lykken has himself tested the validity of Guilty knowledge technique in the past:

all Ss innocent of a crime were correctly classified, while 44 or 50 interrogations of guilty Ss gave guilty classifications, a total of 93.9% correct classification against a chance expectancy of 50% . . . . Detection of guilty knowledge . . . is demonstrably capable of very high validity in those situations where it can be used.

emphryio · 08-14-2002, 05:41 PM

OK. I've never heard of the Guilty knowledge test. I assume it isn't used too often. Possibly it isn't so bad, but something's come up and I won't have time to look into it for a while. Thanks for reponding though.

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08-12-2002, 07:52 AM	#11
Rev. Joshua Junior Member Join Date: May 2002 Location: Atlanta Posts: 63	When I first started training in interrogation, one of the fundamental rules we learned is that the only way to catch someone in a lie was to compare their statement to a known fact. Anything else: polygraphs, voice-stress analysis, neurolinguistics, etc. falls into the category of "indicators of deception." I never said, "I think so-and-so is lying" (except to them, in an attempt to get them to tell the truth). I simply said, "I saw several indicators of deception." For many people, galvonic skin response, accelerated heart rate, etc. can be indicators of deception; but that information is worthless without additional investigative data. Joshua

08-14-2002, 05:41 PM	#14
emphryio Veteran Member Join Date: Oct 2001 Location: WV Posts: 4,369	OK. I've never heard of the Guilty knowledge test. I assume it isn't used too often. Possibly it isn't so bad, but something's come up and I won't have time to look into it for a while. Thanks for reponding though.

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