| I vividly
remember my first lie detector test. It wasn't I who was being
tested but rather a client charged with rape. I was relatively
new to the criminal defense business, having recently been
hired by the State of Vermont as Public Defender of the
Northeast Kingdom (as the three Northeastern most Vermont
counties were called). Before the test began, the test
operator took me aside to explain how it works.
"It's real
simple," he said. "First I explain the basic theory
of the test to the subject: that lying causes anxiety that
shows up on my graphs. Then I explain that the test is called
a polygraph because I graphically track three of their
unconscious physiological responses at the same time. Then I
explain that they can't get away with lying to me since only
someone trained as a yogi can simultaneously control all three
physiological responses (breath, heart rate and galvanic skin
response). Then I wire them up to these graphs and tell them
to pick a number between one and ten. I tell them to answer no
each time I guess a number, even if I guess the right number.
When they answer no to the right number, it always causes a
spike in the graphs. I stop the procedure at that point, tell
them they lied and show them the graphs. Now that they're
convinced that my graphs can read their mind, their responses
go haywire when they lie in the course of my actual
questioning. The fact is, very few of the people I test bother
to lie after this introduction. I get more confessions than
the police ever could by a mere interrogation."
Sure enough, my
client who had up to that point steadfastly proclaimed his
innocence to me, as well as everyone else concerned with his
case, confessed his guilt rather than lie to someone whom he
believed knew when he was lying. I was convinced.
And because I was a
believer, I tended to discourage my clients from submitting to
lie detector tests. The truth was that I could frequently do a
much better job for my clients if I could maintain a personal
belief in their innocence. In some cases, however, the
prosecution made offers of leniency contingent upon my client
being willing to go on the box (as the test is colloquially
called). And so, in the course of my three-year public
defender stint, about a half dozen clients voluntarily
submitted to a lie detector test in hopes of a better deal.
And, with just one exception, they either confessed during the
test or confided their guilt to me after the test indicated
their responses to be deceptive. I remained a believer.
What about the
exception? The results were inconclusive; the operator said he
suspected valium. Since my I knew that my client had a
long-standing valium problem, I thought this was a pretty good
call. In any event, when his case went to trial, the jury, as
ultimate lie detector, didn't believe him and came in with a
guilty verdict.
Are Lie Detectors
Telling the Truth?
You may wonder how, in
the absence of a confession, a polygraph operator can
confidently determine whether a person is lying. Don't most
people -- even innocent ones -- get stressed when being asked
questions that might land them in big trouble? Yes, but the
polygraph operator has techniques to overcome this problem.
Before getting to the nitty-gritty of the issue ("Did you
do it? Were you There? Do you have any personal knowledge of
what happened?") the operator first asks a series of
questions, some of which are emotionally neutral and some of
which are calculated to cause emotional discomfort based on
the test subject's personal circumstances. The subject's
physiological responses to these questions are meticulously
calibrated. Then, when the operator gets around to the core
questions, the responses to those questions can be measured
and compared to the responses produced by the neutral and
control questions. It's true, a lot of devils can live in the
space of relative anxiety measurements, but numerous
independent tests have indicated an accuracy rate in the
80-90% range.
So if these tests are
so accurate, why aren't they required in every situation where
truth is at issue? Why spend billions of dollars on jury
trials and independent prosecutors when we could just
"wire up" the key witnesses and get at the truth
with no fuss and no muss?
The U.S. Supreme
Court recently decided a case that deals with this very
subject. In United
States v. Scheffer, 000 U.S. 96-1133 (1998) the Supreme
Court upheld a military court evidence rule (Rule 707) that
prohibits the use of lie detector results in military trials.
In this case, Scheffer, a military investigator, took a
routine urine test. The test came back positive for
amphetamines. Scheffer then asked for and was given a
polygraph test which showed he had no knowledge of amphetamine
use. At his trial on drug use charges based on the urine test,
Scheffer tried to introduce evidence of his favorable lie
detector results. The court refused to admit this evidence on
the basis of military evidence Rule 707.
Scheffer appealed on
the ground that he should have been able to introduce the test
results as part of his constitutional right "to prepare a
defense." The Supreme Court upheld Rule 707 for these
reasons:
- there is too much
controversy about the reliability of lie detector test
results
- lie detector tests
might undercut the role of the jury in assessing witness
credibility, and
- lie detector tests
create the possibility of vexing side issues about the
reliability of the test.
To Err Can Be
Mechanical
Without question, lie
detector tests are controversial. Putting aside their utility
as interrogation devices, the validity of their results
depends on a lot of things being done right -- the right
control questions, the right neutral questions, the right core
questions, the right interpretation of the graphs, the right
setting for the questioning, and so on. And not all scientific
evaluations have concluded that they are accurate even when
everything is done right.
Many evaluations have
concluded that polygraph results are more likely to be valid
if they show innocence than if they show guilt. This is
because there are lots of situations where a defendant may
have a guilty mind (and thus show up as deceptive on the
polygraph results) but not in fact be guilty. It's the same as
flight. When a defendant runs away from the police or the
scene of the crime, a jury is entitled to infer a guilty mind.
But flight doesn't necessary equal guilt. Innocence, on the
other hand, is much more unequivocal. But even here, some
people are so divorced from morality or a guilty conscience
that they may test honest -- because they are really good
liars or have convinced themselves of a truth that isn't the
truth at all. Last but not least, it may be possible to throw
the results through other methods, such as yogic or
biofeedback training, the "nail in the shoe" trick
(putting a sharp nail in your shoe to cause yourself pain
during the questions to skew the polygraph results), or using
a legal or illegal drug to calibrate one's emotions. Simply
put, there is no way to turn a lie detector test into a slam
dunk. For this reason, most courts will not admit polygraph
results unless both sides to the case agree.
To those who believe
in polygraph tests, the answer to these reliability issues is,
so what? Lots of other types of evidence also have problems.
Consider urine tests, for example. There are lots of things
that can go wrong with a urine test, including laboratory
contamination, false positives and passive smoke. (
In Scheffer's case, however, a urine test was admitted against
him, but the polygraph test was not admissible as a defense.
Of course other types of evidence which are notoriously
unreliable are also routinely admitted into military (and most
other) trials, including eye witness testimony (especially
cross-race eyewitness testimony), evidence of demeanor (he
"looked" guilty) and, as mentioned, evidence of a
guilty mind such as flight.
Man, Machine or Both
The concern that the
polygraph may supplant the jury as the judge of witness
credibility raises some interesting issues. It is founded on a
fear that the jury will abandon its human-based assessment of
a witness's credibility and instead rubber-stamp the machine's
version of the truth. To be sure, if we were wise, we would be
very careful about how much of our important affairs we turn
over to machines. Unfortunately, we've already pretty much
given away the store on this one. Drug tests, DNA matching,
child support calculations, computer-generated profiles and
credit scoring are just some of the types of machine-based
information we use for important commercial, employment and
judicial transactions.
If we can trust
juries to remain independent in the face of the junk science
that is already routinely admitted into evidence -- notably,
psychological profiles and assessments of mental states --
then perhaps we should also rely on juries to remain
independent in the face of a test that, independent studies
indicate, is likely to be right at least 80-85% of the time. |
