If you’ve ever been pulled over by a police officer under suspicion of driving under the influence, you may have experienced what are known as “field sobriety tests”. These tests are administered by officers on drivers they stop on the road and are intended to be a way to determine whether or not a person has been drinking.
The One-Leg Stand Test
The one-leg stand test is one of the two common “divided attention” tests used in Virginia to try and determine if a driver has been drinking. A “divided attention” test is one where the subject is evaluated not only on his or her ability to perform the actual test, but also on how well he or she listens and follows directions.
Like all field sobriety tests, this one has limitations as well. In this test, the police officer will be looking for signs that a driver is intoxicated while asking the subject to stand on one foot. Signs include:
- Using arms for balance
- Hopping to maintain balance
- Putting your foot down
As you might guess, one of the limitations of this test is that even people who are not under the influence of drugs or alcohol can have a hard time standing on one leg without doing one of more of the above.
The Walk-and-Turn Test
The walk and turn is another divided attention test. In this test, drivers are typically asked to take a set number of steps in a heel-to-toe fashion along a straight line. The driver is then asked to turn on one foot and take the same number of steps back down the straight line heel-to-toe.
This test is harder than it sounds, even for people who have not had a drop to drink. Just consider the “signs” that a driver performing the walk-and-turn test might be intoxicated:
- Subject cannot keep balance while listening to instructions
- Subject starts the test before instructions are finished
- Subject pauses to regain balance while walking
- Subject fails to touch their heel to their toe, even just once
- Subject loses balance while walking or steps off of the imaginary straight line
- Subject uses their arms for balance
- Subject does not perform turn as instructed
- Subject takes the wrong number of steps
This test can be a challenge for individuals with balance problems or medical conditions that compromise their balance, or for people taking a medication that might interfere with their balance
The Horizontal Gaze Nystagmus Test
One of the most popular tests is the horizontal gaze nystagmus (HGN) test. The purpose of the HGN test is to determine if a subject can follow (track) an object smoothly at different angles. The belief is that drivers under the influence of drugs or alcohol will be unable to smoothly follow the movement of an object, and their eyes will jerk involuntarily. However, involuntary movement of the eye while attempting to track an object is something that can happen in people who are not intoxicated.
For example, individuals with neurological problems, brain tumors, head injuries or people on certain medications can have trouble tracking an object smoothly with their eyes. These individuals can appear intoxicated according to a HGN test, even if they have not had a drop to drink.
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