In 2013, when he was 24 years old, Nathan Fernandez was arrested for possession of child pornography. To hear him tell it, he was a member of a Deep Web anti-child porn vigilante task force when he developed an attraction to minors. When he was arrested, police found a few dozen child porn files on his computer. "I immediately owned up to it and said I would welcome the chance to go to therapy," Fernandez, now 27, told VICE.
Because he was a first-time offender, the court put him in a halfway house, where he was told he would have to undergo a penile plethysmograph, or a PPG. A few weeks after arriving, he was placed in a small room with a mercury-filled band around the head of his penis and asked to listen to a series of audio narratives detailing a range of scenarios—as he remembers it, an adult couple meeting at a bar and having sex, followed by a teenage girl coming onto an adult man, followed by an adult man violently raping an eight-year-old girl—to see how he would react.
"I was furious," he said. "I had to sit there and listen to all these awful things... I understood why it was all there, but that didn't make it any less degrading."
Fernandez says his test results were "inconclusive," meaning he didn't exhibit a response to any of the scenarios. But the experience of sitting in a room and having his penis hooked up to a monitor nonetheless left him shaken.
Fernandez is one of thousands of sex offenders to undergo PPG, a method of measuring patterns of sexual arousal in response to audio or visual stimuli. Earlier this year, the practice made headlines when it was rumored to have been used in the post-conviction treatment of former NFL safety Darren Sharper, who pleaded guilty to multiple rape charges.
PPG was initially developed by Czech psychologist Kurt Freund in the 1950s as a way to identify heterosexual men who claimed to be gay in order to avoid the Czech military draft. Today, it's most commonly used as a way for forensic psychologists to identify deviant sexual desires, such as pedophilia or violent sexual urges.
"When males get sexually aroused, their penis changes in volume and size. The biology is sound, the physiology is sound," said Dr. Joseph J. Plaud, a clinical and forensic psychologist, in an interview with VICE. Plaud says he's personally administered thousands of PPG exams during his 30-year career. "This is basic biology. There's no interpretation needed, there's no extrapolation needed."
Other experts, however, argue that much like a polygraph, PPG is a form of junk science—an inaccurate, inconsistent way to measure something as complex, amorphous, and subjective as sexual desire.
For one thing, there are ways to stifle an erection. "If you can find a way to keep yourself from being aroused by thinking about your grandmother or puppies or something that's not sexually arousing to you, then you can trick it," Dr. AJ Marsden, a psychology professor at Beacon College in Florida, told VICE.
There's also the issue of what PPG actually measures. While a test subject might be aroused by, say, descriptions of violent, non-consensual sex, that doesn't mean they necessarily have a desire to act on such impulses in real life.
Plus, Marsden added, "a lot of therapists think [PPG is] not the best measure to prove if they are really attracted to the images they show them."
For these reasons, PPG is most often used in the context of treatment, rather than as evidence of guilt or innocence in a sex crime case. Most (but not all) courts reject the admissibility of PPG in court, and in a landmark 2006 case, an appeals court ruled that use of PPG on a man charged with possession of child porn was unconstitutional, as it was "an unreasonable and unnecessary deprivation of a defendant's liberty."
Even still, PPGs can be used both as a post-conviction therapy and in sentencing someone who has committed a sex crime.
In 1991, Ron*, a 59-year-old in Albuquerque, New Mexico, was in the process of divorcing his wife when he was arrested for molesting their daughter. While in police custody, he was asked to take a PPG exam.
"I told them I didn't want to take the test," Ron told VICE. "My attorney said I didn't have a choice. He said if I didn't, the judge would give me a max sentence anyway. It seemed very invasive and demeaning."
Like Fernandez, Ron's test results were inconclusive. Even still, a judge sentenced him to the maximum penalty of 12 years in jail, seven years and 11 months of which he served.
"We're sex offenders," Ron said. "We don't have civil rights."
A PPG can also be used in the private clinical setting, sometimes as a condition of parole. Plaud said the test can be a gauge for the efficacy of a particular treatment, as well as a tool "to try to change or punish that deviant arousal." Marsden sees it more as aversion therapy for sex offender: "It's a degrading type of thing," she told VICE. "Over time, it kind of [helps the offender] associate that this is wrong, I shouldn't do this, this is not acceptable behavior."
Yet failing a PPG can have disastrous consequences for offenders in therapy. "Treatment program people hold sticks and carrots. They say, 'If you don't do this test, that may have negative implications for your progress and treatment, and it may hold you bac,k or we may hold certain privileges for you," Plaud said.
"The PPG wouldn't alter your sentence, but you could indirectly extend your time," Fernandez said. "Every month of therapy [in a treatment center or halfway house] comes at a huge cost to your wallet and to your time."
In January 2016, Fernandez was released from his halfway house. Shortly before he left, he took a second PPG test, during which he says he did not show significant patterns of deviant sexual interest. He's now living at home with his fiancée and two-year-old son, but he says he regularly grapples with symptoms of anxiety, PTSD, and suicidal thoughts—conditions he's struggled with his entire life, and that he says were exacerbated during his time in treatment.
For Fernandez, PPG was not the most humiliating aspect of his treatment. It was merely symptomatic of a larger issue: During his time in treatment, he and his fellow offenders were treated as scientific experiments rather than human beings.
"I felt like I was a test subject for some science experiment that if I fail, I have to stay at this horrible place longer," Fernandez said. "When you're in confinement even though it's not a jail, it's very similar—when it depends on you succeeding or failing at something like that, then that's so much pressure.
"It does not feel like a therapeutic place," Fernandez added. "It feels like a place of torture."
*Name has been changed to protect subject's identity.
Follow EJ Dickson on Twitter.