Fooling the Lie Detector: The Condom Thief

When I was 10, I snuck into the TV room in our house to watch a bit of Ocean’s Thirteen with my older brothers. Before my parents discovered my own egregious crime, I was able to catch a particularly memorable scene of another: a criminal was able to pass a lie-detector test by repeatedly stepping on a thumbtack.

He was hooked up to an impressive machine with whirring sounds, electrode clips, and real-time spikes after each question, all of which made the criminal’s manipulation seem quite clever, at least to a ten year old. It actually turns out to be a widely acknowledged fact that the polygraph test is flawed. The machine measures changes in galvanic skin response – like increases in sweat production, blood pressure and heart rate – due to stressful situations, one of which is lying. Calculating the increase requires a baseline reading, however, meaning that tricking the polygraph just amounts to conditioning oneself to change this baseline reading from “calm” to “stressed” – and that’s as easy as thumbtack-stepping, or even thinking about a painful or scary situation.

It actually turns out to be a widely acknowledged fact that the polygraph test is flawed.

The field of cognitive neuroscience, however, has developed a number of possible ways to solve the problems of the polygraph. Ideas include: (1) infrared photography of the eyes to calculate temperature and blood flow changes, (2) analysis of the scattering of light as it passes through the skull onto the cortex to measure blood vessel contraction and dilation, and (3) measurement of brain waves through electroencephalogram scans of patients presented with crime-scene-related objects or images (Wolpe, 2005).

The most promising technique thus far implements functional magnetic resonance imaging to detect a blood-oxygen-level-dependent (BOLD) signal throughout the brain, which approximates neural activity given the necessity of oxygen for aerobic respiration.

Dr. Steven Laken, a pioneer in the field of fMRI lie detection, patented the first method to be used in court and founded the biotech company Cephos to market this neural lie detection procedure alongside his approaches to forensic DNA analysis (Cephos). The mechanism works through asking a suspect of a crime a series of questions and comparing the observed BOLD signal changes with the changes from control cases where participants were instructed to either lie or tell the truth.

LieDetection_fMRIIf Joe McDogood, for example, is on trial for shoplifting 18 boxes of condoms on New Year’s Eve from his local CVS, the judge might approve tossing him into an fMRI scanner and measuring his neural activity when questioned about the night of December 31st. If the machine shows a particular pattern of increased activity in right anterior cingulate, orbitofrontal, inferior and middle frontal cortex, then Joe is probably toast – guilty as charged (Laken, 2005).

While far from perfect and not yet broadly implemented, this fMRI method is certainly a promising step in improving our techniques for detecting deception. We therefore owe thanks to these recent advancements in cognitive neuroscience for helping get the legal system well on its way toward independence from the easily manipulated method of polygraph testing.

About The Author

Hi! I'm a Molecular Biology major planning on getting certificates in Quantitative and Computational Biology (QCB) and Neuroscience. I'm in the Integrated Science Curriculum here at Princeton, and work in a Neuroscience lab on campus. I'm also in the Chapel Choir, on the board of the Episcopal Church at Princeton (ECP), and on the club running team. And, of course, I write for Innovation! The best science magazine on campus.