The Secrets of Field Sobriety TestsS

Have you been drinking tonight, sir? Oh. Crap. If you're in a car, that's not a question you want to hear from a man in uniform. And if the answer is yes, you're in for the worst pop quiz of your life: the field sobriety test.

Look, you should not drive drunk. Ever. No, seriously, not ever. The goal of this piece is not to show you how to beat a field sobriety test—in most cases, no amount of preparation can help you anyway. But you know what? They make for one hell of a drinking game. Try 'em out for yourself—from the comfort and jail-free safety of you own home. May the best drunk win!

It's Friday afternoon, you've made it through the long week, and it's time for Happy Hour. Gizmodo's weekly booze column is a cocktail shaker full of innovation, science, and alcohol. Offisher, I swear, I only hag free drinks.

The Big Three

The National Highway Traffic Safety Administration has established three tests as the Standardized Field Sobriety Test. You may find a rogue officer who throws something else at you, but because the standardized tests are mostly likely to hold up in court, these are the ones you'll probably encounter.

The Horizontal Gaze Nystagmus (HGN) Test.

You've seen this test in movies and public service announcements. It's the one where the officer has you watch a moving a pen or a flashlight. Nystagmus is an involuntary shaking of the eyes that usually only occurs at the extremes of your periphery. But when a person is intoxicated, it can occur at less steep angles.

So the officer will have your eyes follow the object, slowly, back and forth. He or she will be watching for jerkiness in the way your eyes track the object, looking for that telltale shake when they're off at the sides. If nystagmus occurs within 45 degrees of center, you could be in trouble. A person without nystagmus should be able to follow the object smoothly, and when they look at a still object at 45 degrees, they should be able to do so steadily.

If you failed this test, you likely have a blood-alcohol content (BAC) of 0.08 or greater. The NHTSA estimates this test to be 88-percent accurate. But here's the thing: There are literally hundreds of known causes of nystagmus, most of which have nothing to do with intoxication. Some people's eyes just behave that way, which must be rather inconvenient for sober people at a DUI check.

The Walk-and-Turn (WAT) Test

You've probably seen this one, too. The cop tells you to "walk the line," taking nine heel-to-toe steps, while looking down and counting out loud. At nine steps, you pivot on one foot, turn around, and walk nine heel-to-toe steps back. You have to keep your hands at your sides, your eyes down, and you can't stop, waver, or really screw it up at all.

This is what's known as a "divided attention" test. The striatum, a part of the brain linked to multitasking, is compromised when someone drinks to excess. The effect is severe when the attention span is divided between mental and physical tests. The NHTSA website says the officer is looking for eight signs of impairment. You're in trouble if you:

  • cannot keep balance while listening to the instructions
  • begin before the instructions are finished
  • stop while walking to regain balance
  • do not touch heel-to-toe
  • step off the line
  • use your arms to balance
  • make an improper turn
  • take an incorrect number of steps

There are a lot of things to remember here. That's the idea—in addition checking your balance, the officer is looking at how accurately you can follow instructions. Alcohol has a serious impact on the hippocampus—the part of the brain associated with the creation of new memories. It's hard to follow multiple instructions if you're having a hard time remembering what they are. The NHTSA claims the Walk-and-Turn test is 79 percent accurate.

The One-Leg Stand (OLS) Test

Like the Walk-and-Turn test this is a divided attention test that also checks to make sure you won't fall flat on your face. You are instructed to stand with one foot about six inches off the ground, and count aloud by one-thousands until you're told to lower your foot. The officer times you for 30 seconds. He or she will look for four main indicators of intoxication: Swaying while balancing, using arms to balance, hopping to maintain balance, and putting the foot down. It is 83 percent accurate.

Combined, the NHTSA claims that those three tests are 91 percent accurate. There are a few other less common tests folks may encounter instead.

The Rhomberg Balance test

For this one, you are asked to stand up straight, close your eyes, tilt your head back, and silently estimate the time it takes for 30 seconds to elapse. You'll be inspected for an inability to stand steadily, eyelid tremors, the need to peek to maintain balance, muscle tension, and any odd statements you may make. (That's true for all of these tests). The officer is also testing your internal clock's accuracy. It will be slow if you're drunk, and sped up if you're on stimulants. If you've smoked pot, 30 seconds might seem like a half hour.

Finger to Nose

This test requires you to place your feet together, standing straight, with your eyes closed. Upon the officer's order, bring your index finger to your nose. This is a balance test. Alcohol is well-known to affect one's equilibrium. The officer is looking for body sway, body tremors, eyelid tremors, muscle tension, or the big tell—missing your own nose—as well as any statements made by the accused to support a finding of intoxication.

Finger Tap Test

Also known as the Finger Counting Test. In this exam, the officer directs you to hold out one hand, palm up, and touch the tip of each finger to the tip of your thumb. You are told to count out loud after each tap, forward and backward, for three consecutive sets. You can flunk it if:

  • You start the test too soon.
  • You can't count as directed.
  • You don't touch your fingers to your thumbs.
  • You perform the wrong number of sets.
  • You stop the test before you're told to do so.
  • You just can't follow the instructions, period.

Miscellaneous Evaluations

There are even more uncommon field sobriety tests you may encounter. These include: Hand clapping, counting backwards, reciting the alphabet forwards or backwards (a notorious test that isn't all that easy even when sober). There's also this one, from The Man With Two Brains. Very difficult.

While any of these tests may have scientific, neurological implications, it's important to note that the evaluation of these is entirely subjective. If the cop thinks you're drunk, under circumstances that would normally lead to an arrest in that part of the world, you'll go to jail. It will be his word against yours. You can refuse to take these tests (as well as a BAC-measuring breathalyzer test), but that will typically result in your arrest and likely a suspended driver's license. Don't drink and drive.

You and your friends could turn these tests into a sort of drinking game. You may already have your own unofficial tests—tell us!

Otherwise, enjoy your nystagmus responsibly, and tune in next week for a very special Happy Hour.

Photo credit: (C) Lisafx / Stockfresh