The process of polygraph testing

  • Tuesday, July 22, 2014

Staff photo by Teddy Kulmala Investigator Tommy Platt, left, demonstrates a polygraph examination using Capt. Eric Abdullah as the examinee. The Aiken County Sheriff's Office conducts about 200 exams per year for both criminal and employment purposes.


Can you handle the truth? Regardless, it’s Tommy Platt’s job to find it out. Platt, an investigator with the Aiken County Sheriff’s Office, is also the agency’s polygraph examiner.

Also known as a “lie detector test,” a polygraph exam measures physiological reactions from telling a lie. The Sheriff’s Office administers polygraph exams as part of the employment process for anyone seeking a job at the agency, but also for criminal investigations.

How it works

The machine measures a person’s breathing, heart rate and galvanic skin reflex (or sweat gland activity), according to Platt, who has been giving exams for more than six years.

“When you’re asked a question or a stimulus, your brain goes to your memory lobe and searches for the answer,” Platt said. “If it finds that answer, and you have a memory of something you’ve done, it flashes a picture in your head to help you remember details and descriptions.”

That process is called mental imaging, he said. If you wanted to lie in response to a question, instead of going with the “memory” side of the brain, you go with the “create” side.

“You create a lie by saying ‘no,’” Platt said. “That causes a conflict with the brain. It’s saying one thing, you’re saying another – it’s going to react to that and compensate, and sends a signal down the sympathetic nervous system telling the heart, lungs and sweat gland activity to change.”

In the seat of a large leather chair in the polygraph examination room is a sensor pad. Platt said the No. 1 countermeasure of people trying to beat a polygraph exam is tensing up muscles to change their physiological reaction, which will be picked up by the pad.

The other instruments that are part of the exam are a blood pressure cuff to measure your heart rate, tubes that stretch around your chest and abdomen to monitor breathing, and two finger plates to measure sweat gland activity.

The exam

The process for an average exam takes between one-and-a-half to four hours, depending on the substance of the exam, Platt said. After the paperwork comes “rapport building,” during which Platt explains the polygraph process to the examinee.

Platt said he’ll get the investigator to brief him before an exam, then he’ll get the examinee’s side of the story. To start the exam, he’ll ask simple questions such as “Are you sitting down?”

“Any type of nervousness or anxiety, we get it out of the way with these questions,” he said.

Examinees are instructed not to move, not to take deep breaths or purposefully clear their throat or cough, which could disrupt the exam.

People have tried to “beat” polygraph exams, and there are many websites that purport to offer tips on how to beat an exam. Platt said officers from the Navy SEALs, CIA and other special forces will go to school specifically to learn how to beat a polygraph exam, so it’s not likely someone can learn the same thing from a website or pamphlet.

How it’s used

Platt said he administers between 150 and 200 exams each year. About 75 percent of them are for criminal investigations while the remaining 25 percent are pre-employment.

While there are many different studies speculating the accuracy of polygraphs, Platt said they are generally about 95 percent accurate.

If an examinee is under the influence of illegal drugs, anti-depressants, beta blockers or alcohol, that can skew the test results, Platt said.

The results can be used in trials, but before a suspect is charged, the attorneys on both sides must sign a stipulation order stating that the polygraph results will be admitted no matter the turnout, Platt said, adding that this rarely happens.

In addition to all Aiken County law enforcement agencies, the Sheriff’s Office also offers polygraph exams for Barnwell County, Edgefield County and McCormick County, and has even completed them for state agencies.

Platt administers private exams, and can offer private criminal exams anywhere other than Aiken County. He is also contracted to administer exams as part of fishing tournaments.

Because the payout is so large for the top finishers, Platt said the winners are given polygraph exams to ensure they didn’t cheat.

“It’s so easy to cheat in a fishing tournament,” he said. “You catch a bass and grab four ounces of lead and stuff it down the fish’s throat – the fish is going to be alive and that’s four more ounces.”

Teddy Kulmala covers the crime and courts beat for the Aiken Standard and has been with the newspaper since August 2012. He is a native of Williston and majored in communication studies at Clemson University.

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