You’ve probably heard of “lie detector” machines – you hook
a person up to some kind of machine, ask them some questions, and some needles
move around on a piece of paper, making cool-looking patterns, and the operator
looks at these outputs and can tell if you’re lying. More accurately, what
you’re thinking of is a polygraph test. You should know that these machines
can’t simply tell the operator if a person is lying or not. What a machine does
is measure a few objective physiological indicators, including heart rate,
blood pressure, the rate of breathing, and perspiration.
These properties tend to change when a person is nervous, and people often get nervous when they’re telling a lie. So, in theory, a trained operator can figure out if you’re lying or not, by looking at these indicators.
There are quite a few problems with this system, however.
While the things being observed (blood pressure, heart rate, etc.) are
objective facts, the operator of the polygraph has no way of knowing for sure
what’s affecting them, so his or her interpretation of them will necessarily
involve some guesswork and subjectivity.
Estimates of accuracy vary (some proponents claiming that it’s in the 90% range, with a skilled operator), while others insist that the accuracy rate isn’t much better than chance.
As a result of this uncertainty, the federal government and
just about every state in the
There have been many technological developments, especially in neuroscience, since then. As a result, some people have suggested using new technology to look directly at the source of lying: the brain.
One theory is that we can use magnetic resonance imaging (MRI) to
image a person’s brain. Some studies have shown that when lying, we use a
different part of our brain than we do when we’re recounting truthful
information. This makes a good bit of sense – when you’re telling a truthful
story, you’re simply describing things that you actually remember. When you’re
telling a lie, you have to exert mental effort to keep your story straight and
sometimes come up with a story on the fly. Obviously, you’ll be using different
parts of your brain to do this.
Once we know what parts of our brain we use to tell lies, we
can use an MRI to measure brain activity while asking somebody a question. If
the part of the brain responsible for lying shows a spike in activity, you can,
in theory, tell if a person is lying with much more accuracy than a polygraph.
One enterprising lawyer in
I personally think that this was the right decision. The MRI
technology is very fascinating, but, as the court noted, it’s still in its
When a new technology which has the potential to unearth new types of evidence comes along, courts are, rightfully, fairly conservative about adopting it. For example, it has been known for centuries that each person’s fingerprints are unique. However, it wasn’t until the 1800s that they were first used as evidence in a criminal trial. It’s not that courts are averse to new forms of evidence; but when a person’s life, freedom, or fortune is on the line, a court better be darn sure that any evidence they admit is highly reliable. Fingerprints took time to become sufficiently established to meet this standard. It also took several years before courts started accepting DNA “fingerprints” as evidence.
Both of those developments revolutionized forensic science, and how the criminal justice system functions. MRI lie detection, if it proves reliable, has the potential to do the same. However, just as we have in the past, we need to be cautious before we start to rely on this technology to determine a person’s civil or criminal liability, given what’s at stake in many of these cases.
By: Rusty Shackleford